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Effect of Different Extraction Methods on Quality Characteristics of Rapeseed and Flaxseed Oils

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Research Article

Effect of Different Extraction Methods on Quality

Characteristics of Rapeseed and Flaxseed Oils

Shuzhen Wang ,

Jinying Wang ,

Guoxin Dong ,

Xia Chen ,

Shulin Wang ,

Feng Lei ,

Xuebing Su ,

and Qin Bai

College of Agriculture and Animal Husbandry, Qinghai University, Xining 810016, China

State Key Laboratory of Plateau Ecology and Agriculture, Qinghai University, Xining 810016, China

Qinghai Tongda Oil Processing Co. Limited, Haidong 810600, China

Correspondence should be addressed to Jinying Wang; wangjinying0128@126.com

Received 25 May 2022; Revised 11 August 2022; Accepted 29 August 2022; Published 19 September 2022

Academic Editor: Vita

Di Stefano

which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

is study reports the eect of roasted pretreatment combined with screw press, hydraulic press, and Soxhlet extraction methods

on various quality indexes of rapeseed and axseed oils, including the oil yield, sensory indexes (color, smell, clarity, viscosity, and

colligation score), physicochemical properties (acid value, peroxide value, saponication value, moisture and volatiles), major

components (fatty acid composition and triglyceride composition), and minor components (volatile compounds, total phenols,

and vitamin E contents). e results indicated that the oil yield, sensory indexes, physicochemical properties, fatty acid

composition, volatile compounds, total phenol, and vitamin E contents in vegetable oils have been signicantly aected by

dierent extraction methods. e yields of rapeseed and axseed oils of Soxhlet extraction method were increased by 30.10%–

73.90% and 6.30%–54.40%, respectively, compared with other treatment groups. In addition, roasted pretreatment signicantly

increased the yields of oils by 4.10%–25.00% and 6.70%–23.15%, respectively, compared with the untreated group. e contents of

linolenic acid and vitamin E in rapeseed and axseed oils extracted from screw press method were higher. In particular, the

linolenic acid content of cold-pressed rapeseed oil extracted by screw press increased by 1.50%–23.80% compared with other

treatment groups. In addition, the contents of vitamin E in cold-pressed rapeseed oil and axseed oil obtained by screw press

increased by 1.22%–78.91% and 3.00%–18.80%, respectively. e Soxhlet extraction could improve oil yield and total phenol

content, but the quality of the oil was inferior due to high acid values (0.93–3.36 mg KOH/g) and peroxide values (0.70–5.23 meq

/kg). Furthermore, the hydraulic press method could extract vegetable oils with excellent sensory scores. e roasted pre-

treatment gives the rapeseed and axseed oils a good smell. e major volatile compounds in rapeseed and axseed oils were

aldehydes, acids, alcohols, heterocycles, and ketones. Dierent extraction methods and pretreatment had no signicant eect on

the compositions and contents of triglycerides. is study provides a basic understanding on the selection of appropriate oil

extraction techniques for oil extraction at a large scale.

1. Introduction

Rapeseed is one of the major edible vegetable oil seeds with

high oil contents (38%–50%) [1]. Canada and China are the

top two producers of rapeseeds worldwide, and rapeseed oil

is mainly consumed in China [2]. As the traditional bulk

edible oil in China, natural rapeseed oil is rich in omega-3

polyunsaturated fatty acids, and the dominant type is

linolenic acid, which represents ∼8% of total fatty acids [3].

Rapeseed oil also contains many cardioprotective

micronutrients including antioxidant vitamins such as vi-

tamin E [4], polyphenols such as sinapic acid (free phenolic

acid), sinapine (esteried form; the most abundant species)

[5], and phytosterols [6], which have strong antioxidant,

senility-delaying, and antihypercholesterolemic activities

[7]. In particular, vitamin E oers protection against oxi-

dative deterioration and maintains the sensory properties of

foods [8].

Oilseed ax (Linum usitatissimum L.) is one of the most

important oil crops in the alpine regions of North and

Hindawi

Journal of Food Quality

Volume 2022, Article ID 8296212, 12 pages

https://doi.org/10.1155/2022/8296212

Northwest China [9]. As an ancient edible vegetable oil,

axseed oil contains an abundant omega-3 fatty acids and

small amounts of other components such as polyphenols

and phytosterols. Omega-3 fatty acids have been reported to

be associated with a lower risk of cardiovascular disease [10],

diabetes [11], and cancer [12].

Oil extraction methods play an important role in veg-

etable oil yields, qualities, and oxidation stability. ere are

many technical processes involved in the extraction of oils

from the same origin, making the nal products dierent in

physicochemical proprieties and nutritional values [13, 14].

In China, there are many traditional extraction methods,

such as solvent extraction and mechanical pressing. Screw

press is one of the oldest and most popular methods for oil

production worldwide [15] because the technique is easy to

operate and maintain. However, the method could only

partially defat the seeds. erefore, the resulting press cake

must be defatted by percolation with hexane. Another

mechanical pressing method is the hydraulic press method,

which is also one of the oldest and simplest methods for oil

extraction. Although the hydraulic press method results in a

lower oil yield than the solvent extraction method, the

method gives oil higher quality. One study has reported that

oils extracted with the hydraulic press tend to contain a

higher content of phytosterols [16]. Solvent extraction is one

of the cheapest and most ecient techniques for producing

edible oils [17], such as Jojoba oil, soybean oil, palm oil, and

jatropha oil. In the solvent extraction method, oil seeds are

pretreated (grind) and then placed in a suitable solvent to

extract the oil from the solid matrix to the liquid phase.

Zanqui et al. [18] showed that the average oil yield of axseed

oil extracted by the subcritical n-propane uid extraction

(SubFE) method was 28%, and it had higher purity and

higher oxidation stability.

Because it is dicult to extract all of the oil contents from

seeds, particularly by mechanical methods, it can be bene-

cial to develop a pretreatment method that generates oil

with a high yield from oilseeds while maintaining the nu-

tritional and quality characteristics. Researchers have re-

cently studied several pretreatments for improving oil yields,

such as roasted, freeze-thaw, microwave irradiation [19] and

dielectric [20] and ultrasound-assisted hexane extraction.

Roasting is a pretreatment method of oilseeds which can

provide signicant benets to seeds used for consumption

and oil extraction. is method promotes some desirable or

undesirable changes in chemical, physical, and nutritional

characteristics [21, 22]. Roasting seeds before oil extraction

has been shown to have a signicant impact on oil as it helps

to generate a distinctive aroma and improve the oxidative

stability of the oil due to by-products formed as a result of

the Maillard reaction [23].

e main objective of this study is to compare the

eects of dierent extraction methods, including screw

press, hydraulic press, and Soxhlet extraction methods, on

the quality of rapeseed and axseed oils. e major

components (fatty acid composition and triglyceride

composition) and minor components (volatile compo-

nents, vitamin E, and total phenol contents) were analyzed

to assess the quality of oils. is study provides data for

processors to select the extraction methods that result in

the optimal oil quality.

2. Materials and Methods

2.1. Samples and Chemicals

2.1.1. Samples. Rapeseeds “Qingza No. 12” and axseeds

“Dingya No. 18” were collected from the Xining and Guide

in Qinghai (harvest date: March 2021). e seeds were stored

at 4

C until extraction.

2.1.2. Reagents. Chromatographic-grade n-heptane and

methanol were purchased from Damao Chemical Reagents

Co. (Tianjin, China). Methyl undecanoate, methyl hex-

adecanoate, methyl stearate, methyl oleate, methyl linoleate,

and methyl linolenate were purchased from Sigma Aldrich

Trading Co. (Shanghai, China).

2.2. Oil Extraction

2.2.1. Sample Pretreatment. Seeds were cleaned and sieved

to remove debris. e whole seeds are roasted in an elec-

tromagnetic oven, the roasted temperature is 160

C–180

the time is 10 min, and the seeds are constantly turned

during the roasting to avoid burning. Untreated seeds were

used as controls, which represent the cold application.

2.2.2. Screw Press. Vegetable oil was extracted using an XZ-

Z505W horizontal screw press machine (Guangzhou Xuz-

hong Food Machinery Co., LTD, China). e output of the

screw press was 0.36 t/h. Gravity fed samples at the hopper of

the screw press, and the oil was collected at the outlet. e

temperatures of the screw press were 160

C–180

C. Oil

temperature was 40

C. To slow down oil oxidation and

remove some impurities, after centrifugation at 2500g for

15 min, the oil samples were kept in a 250 mL brown bottle

and stored in a refrigerator at 4

C until further analysis.

2.2.3. Hydraulic Press. Oilseed akes were packed in a cloth

sheet and placed in a metallic pressing cylinder. e raw

material capacity of the hydraulic press is 3–6 kg. e oilseed

akes inside the metallic cylinder were then preheated at

C–70

C. While heating, the metallic cylinder was pressed

using an XZ-Z505W hydraulic press machine (Guangzhou

Xuzhong Food Machinery Co., LTD, China). At a pressure

of 50 MPa for 15 min, oil temperature was 50

C. After that,

the oil was centrifuged at 2500g for 15 minutes and then

stored in a 250 mL brown bottle at 4

C until subsequent

analysis.

2.2.4. Soxhlet Extraction. Vegetable oil was extracted from

these samples with a SOX406 fat analyzer (Shandong Hai-

neng Scientic Instrument Company, China). In a typical

extraction, ground dried seeds (6 g) were packed in a thimble

and then extracted with petroleum ether (100 mL). e

immersion, washing, and recovery steps were performed at

2 Journal of Food Quality

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C, and each step lasted for 2, 5, and 1 h, respectively. All

the extracted oils were collected, and the residual solvent was

removed using a draught drying cabinet. e oil was stored

in 250 mL brown bottle at 4

C until further analysis.

2.3. Analytical Methods

2.3.1. Sensory Analysis. Oil sensory analysis was carried out

according to Szydłowska-Czerniak et al. [24]. Fifteen pro-

fessional evaluators were employed to evaluate the color,

smell, clarity, viscosity, and colligation score of the samples.

e samples were given scores on a 5-point scale ranging

from 0 (extremely low) to 5 (extremely high).

2.3.2. Physicochemical Properties. Standard methods of the

International Organization for Standardization (ISO) were

used to determine the acid value (ISO 660, 2020), peroxide

value (ISO 3960, 2017), saponication value (ISO 3657,

2020), and moisture and volatiles contents (ISO 665, 2020).

2.3.3. Fatty Acid Proﬁle. Fatty acid contents were deter-

mined according to laboratory-established methods [25].

(1) Sample Preparation. 100 ±0.1 mg of oil samples,

40 mL of methanol, 1 mL of potassium hydroxide methanol

(1 mol/L), and 0.5 mL of methyl undecanoate (10 mg/mL;

internal standard solution) were mixed until homogenous,

and the mixture solution was then shaken in water bath at

C for 60 min until the solution was clear. en, the ester

layer was extracted using n-heptane. e FAME solutions

were diluted with n-heptane prior to injection into the GC

column.

(2) GC-FID Analysis. e prepared samples were

autoinjected into a Shimadzu GC-2030 gas chromatograph

(Shimadzu, Japan) equipped with a fused silica Wonda Cap

WAX column (60 m in length × 250 μm in

diameter × 0.25 μm). e injector and detector temperatures

were xed at 250

C. High-purity hydrogen was used as the

carrier gas owing at a ow rate of 1 mL/min. e injection

volume was 1 μL, and the injection was carried out at a split

ratio of 46 : 1. e column temperatures were programmed

as follows: initial oven temperature was set at 100

C and held

for 13 min; raised to 180

C at 10

C/min and held for 6 min;

raised to 200

C at 1

C/min and held for 20 min; and nally

raised to 230

C at 4

C/min and held for 10.5 min.

(3) Qualitative and Quantitative Analysis. Qualitative

analysis of fatty acids was carried out based on the retention

time of 5 types of fatty acid methyl esters, and quantitative

analysis was conducted using the internal standard method.

2.3.4. Triglyceride Proﬁle. Triglyceride contents were de-

termined according to laboratory established methods [26].

(1) Sample Preparation. 1 ± 0.1 g of oil was mixed with the

mobile phase (acetonitrile : isopropanol (30 : 70, v/v)) in a

10 mL volumetric ask. After swirling for 1 min until

completely mixed, the mixture was ltered through a

0.45 um nylon lter membrane in an injection ask before

subjecting to high-performance liquid chromatographic

analysis.

(2) HPLC-ELSD Analysis. Triglycerides were analyzed

using a LC-20AD high-performance liquid chromatograph

(HPLC) (Shimadzu, Tokyo, Japan) equipped with an

evaporative light-scattering detector (ELSD) and a C18

column (5.0 μm, 4.6 × 250 mm). e column temperature

was set at 40

C, and the detector temperature was set to 30

Sample at a volume of 5 μL was injected into the HPLC and

then eluted with acetonitrile : isopropanol (30 : 70, v/v) at a

ow rate of 0.5 mL/min.

(3) Qualitative and Quantitative Analysis. Based on their

ECN partitioning, which occurs in the same order as the

number of carbon atoms in ECN (from small to large), each

triglyceride was qualitatively analyzed based on the order in

which the peak emerged. e area normalization method

was used for quantitative analysis.

2.3.5. Volatile Compounds. Volatile compounds were de-

termined by reference to the method of Ojeda-Amador et al.

with minor modications [27].

(1) Solid-Phase Microextraction (SPME). Solid-phase

microextraction (SPME) was performed using a 50/30 μm

PDMS/DVB/CAR PK3 ber (Beijing, China). 6 ±0.1 g of oil

was transferred into a 15 mL glass vial, which was then

inserted with a microstirring bar. e vial was placed in a

magnetic water bath at 80

C and stirred magnetically. After

allowing the sample to equilibrate for 20 min, the needle of

the SPME device was inserted into the vial, and the ber was

allowed to expose to the headspace of the sample. After

40 min of exposure, the ber was retracted from the vial

headspace and then inserted into the gas chromatograph

injector.

(2) GC-MS Analysis. An QP2020 NX series gas chro-

matograph-mass spectrometer (Shimadzu, Japan) was used

to analyze volatile compounds adsorbed on the SPME ber.

e separation was carried on an InertCap-wax column

(30 m × 0.25 mm, 0.25 μm). Helium was used as the carrier

gas owing at a ow rate of 1.0 mL/min. e injector was

operated at 250

C in a split mode at split ratio of 50 :1. e

SPME ber was kept in the injector for 5 min. e column

was maintained at a temperature of 40

C for 2 min; after that,

it was heated to 220

C at a rate of 5

C/min and held for

10 min. e MS conditions were as follows: source tem-

perature, 150

C; transfer line temperature, 260

C; acquisi-

tion mode, electron impact (EI 70 eV) at 3 scans per second;

and mass range, 235–350 m/z.

(3) Qualitative and Quantitative Analysis. In qualitative

analysis, the spectra of the compounds were searched against

the NIST 14 standard spectrum library and compared with

those of the standard. e area normalization method was

used in quantitative analysis.

2.3.6. Total Phenols. Total phenols content was estimated by

the Folin-Ciocalteu colorimetric method, based on the

procedure of Suri et al. [28], using gallic acid as a standard

phenolic compound.

Journal of Food Quality 3

(1) Sample Preparation. Oil sample was weighed to

0.5 ±0.1 g and then subjected to extraction with 2.5 mL of

70% methanol solution. After 5 min, the sample was

ultrasonicated for 5 min, refrigerated for 5 min, and then

centrifuged for 5 min at 2500g, and the supernatant was

transferred to a 10 mL volumetric ask. e above process

was repeated 3 times, and the volume was xed with 70%

methanol solution. In another 10 mL volumetric ask, 1 mL

of extraction solution, 1 mL of diluted Folin-Ciocalteu (FC)

reagent, and 3 mL of 10% sodium carbonate solution were,

respectively, added. Pure water was added for volume

measurement and then let stand in darkness for 2 h.

(2) Qualitative and Quantitative Analysis. e absor-

bance at 765 nm was measured using a UV-1780 spectro-

photometer (Shimadzu, Japan). e total phenol content

was calculated by the equation obtained from the standard

curve of gallic acid, which was: Y � 0.0799X +

0.0368 R

� 0.9981.

2.3.7. Vitamin E. Vitamin E was measured based on Faghim

et al.’s method with slight modications [29].

(1) Sample Preparation. Sample was accurately

(Y � 0.0799X + 0.0368 R

� 0.9981) weighed to 1.5 ±0.1 g

and then placed in a 50 mL brown centrifuge tube. After 0.2 mL

of 50% potassium hydroxide, 0.6 mL of anhydrous ethanol, and

0.2 mL of 16 g/L pyrogallic acid were added, the tube was

shaken for 1 min. Saponication was carried out in a water bath

at 80

C for 30 min in darkness. After the reaction was complete,

the tube was cooled down to room temperature in cold water.

Five milliliters of petroleum ether was added to the saponi-

cation reaction solution, and the mixture was vigorously mixed

by oscillation for 1 min; after that, it was let stand for 15 min.

e petroleum ether layer was transferred into another 50 mL

brown centrifuge tube. e extraction step was repeated using

5 mL and 3 mL of petroleum ether. e three extracts were then

combined and dried under nitrogen stream at room tem-

perature. e dried sample was redissolved in 0.2 mL of

chromatography-grade methanol, ltered through a 0.22 μm

membrane, and then immediately subjected to analysis.

(2) HPLC-DAD Analysis. e content of vitamin E in oil

samples was analyzed by 1100-VWD HPLC equipped

(Agilent, China) with a photodiode array detector, of which

the emission wavelength was set at 300 nm. e injection

volume was 10 μL. e separation was carried out using a

ermo Scientic Syncronis HPLC column with dimensions

of 250 mm × 4.6 mm. e ow rate was set at 1.3 mL/min.

Methanol and water at a ratio of 92/8 (v/v) were used as the

mobile phase.

(3) Qualitative and Quantitative Analysis. Qualitative

analysis was carried out using vitamin E standard, and

quantitative analysis was conducted using the standard curve,

of which the equation was Y � 1.3901X + 0.1644 R

� 0.999.

2.4. Statistical Analysis. e data was statically analyzed

using SPSS 26.0 (IBM, USA). To identify signicant dif-

ferences among the extraction methods, two-way analysis of

variance (ANOVA) was performed at 95% signicance level

(a � 0.05). Graphs were prepared using Origin 2018

(OriginLab, USA). All results were expressed as arithmetic

means of three independent measurements ± standard de-

viations (SDs).

3. Results and Discussion

3.1. Oil Extractions. Figure 1 shows the eect of dierent oil

extraction methods on rapeseed and axseed oil yield.

Figure 1(a) shows that the rapeseed oil yield extraction by

the Soxhlet extraction method is the highest, which is

39.10%–40.70%, while the rapeseed oil yields of screw press

and hydraulic press method are 24.00%–30.00% and

23.40%–26.20%, respectively. e yield of the hot-pressed

treatment group was higher than that of the cold-pressed

treatment group, which indicated that roasted pretreatment

could increase the rapeseed oil yield. is may be because

roasted pretreatment destroys the cellular structure of the

seeds, making the oils easier to extract [30]. Dierent oil

extraction methods and pretreatment had signicant eects

on rapeseed oil yield (P <0.05); the yield of rapeseed oil

prepared by the Soxhlet extraction method increased by

30.10%–73.90% compared with other methods. e yield of

rapeseed oil in hot-pressed treatment increased by 4.10% to

25.00% compared with that in cold-pressed treatment.

Figure 1(b) shows that the yield of axseed oil obtained

by dierent oil extraction methods is Soxhlet extraction

(31.88%–34.50%) >screw press (24.36%–30.00%)

>hydraulic press (22.34%–23.84%). e Soxhlet extraction

method has the highest yield of axseed oil, but its appli-

cation in the food industry is limited due to the presence of

organic solvent residue in the oil. In contrast, the yield of

axseed oil extracted by screw press was 8.07%–34.28%

higher than that of hydraulic press, which was more suitable

for producing axseed oil. Dierent pretreatments had

signicant eects on the yield of axseed oil, and the yield of

cold-pressed axseed oil was 6.70%–23.15% lower than that

of hot-pressed axseed oil.

3.2. Sensory Quality. e sensory quality of rapeseed and

axseed oils prepared by dierent oil extraction methods

was evaluated based on various indicators including color,

smell, clarity, viscosity, and colligation score, and the results

are shown in Figure 2. As illustrated in Figure 2(a), the

sensory scores of rapeseed oil extracted by hydraulic press

were highest, followed by those of oil extracted by screw

press and Soxhlet extraction. Additionally, hot-pressed

rapeseed oil had a better smell, while cold-pressed oil had

better color and clarity.

e sensory quality of axseed oil was similar to that of

rapeseed oil. In particular, hot-pressed axseed oil had a

better smell than cold-pressed axseed oil. is indicates

that using roasting as a pretreatment step for rapeseed oil

and axseed oil extraction could increase consumer satis-

faction. is is consistent with research by Yin et al. [31]

which showed that consumers prefer roasted sesame oil to

cold-pressed sesame oil. Based on the sensory quality, hy-

draulic press is the most suitable method for extracting oils

from rapeseed and axseed.

4 Journal of Food Quality

3.3. Physicochemical Properties. e physicochemical

properties of oils extracted from oilseeds using dierent

extraction methods are shown in Table 1. Acid values of

the extracted rapeseed and axseed oils were 0.51–3.36 mg

KOH/g and 0.82–1.59 mg KOH/g, respectively, and their

peroxide values were between 0.22 and 5.23 meq O

/kg.

e highest acid and moisture values were determined in

Soxhlet extraction in hot rapeseed oil. e highest per-

oxide value was determined in Soxhlet extraction in hot

axseed oil. In particular, the acid values of hot-pressed

rapeseed oil extracted by Soxhlet extraction were

2.11∼6.58 times those of other treatments. is might be

Screw press Hydraulic press Soxhlet extraction

Oil sample

** **

Oil yield (%)

Hot

Cold

(a)

Screw press Hydraulic press Soxhlet extraction

Oil sample

Hot

Cold

Oil yield (%)

(b)

Figure 1: Oil yield of rapeseed and axseed oils extracted by dierent extraction methods. (a) Rapeseed oil and (b) axseed oil.

Colligation

score

Viscosity

Smell

Color

Clarity

Hot pressed of screw

Hot pressed of hydraulic

Hot pressed of soxhlet

Cold pressed of screw

Cold pressed of hydraulic

Cold pressed of soxhlet

(a)

Colligation

score

Viscosity

Clarity

Smell

Color

Hot pressed of screw

Hot pressed of hydraulic

Hot pressed of soxhlet

Cold pressed of screw

Cold pressed of hydraulic

Cold pressed of soxhlet

(b)

Figure 2: Sensory scores of rapeseed oil and axseed oil extracted by dierent extraction methods. (a) Rapeseed oil and (b) axseed oil.

Journal of Food Quality 5

because the oil’s water content was too high, which was

1.54%.

Moreover, with the increase of temperature, the hy-

drolysis reaction of oil accelerated; thus, the acid value

increased. e peroxide value of hot-pressed axseed oil

extracted by Soxhlet extraction was determined to be

5.23 meq O

/kg, which was an increase of 1.26%–22.77%

compared with that of oil in other treatment groups. e rise

in the peroxide values of rapeseed and axseed oils obtained

from the Soxhlet extraction system may be attributed to the

solvent used, the applied heat, and the presence of oxygen in

the system [32]. Similar results were reported for axseed

oils. Kulkarni et al. [33] observed that oil extracted by

Soxhlet method had the highest peroxide value, whereas the

peroxide value of commercial screw press expeller was the

lowest. e saponication values of rapeseed and axseed

oils extracted by dierent methods were found to be between

173.21 and 199.88 mg/g; these values reect not only the

average molecular weight of the oils but also their purity. e

saponication value of hot-pressed rapeseed oil extracted

using Soxhlet extraction was the lowest with a value of

173.21 mg/g, and this may be due to the fact that the oil

contains some impurities that cannot be saponied.

3.4. Fatty Acid Proﬁle. e fatty acid proles of rapeseed and

axseed oils extracted by dierent methods are presented in

Table 2. Five major fatty acids presented in the two types of

oils were palmitic acid (C16 : 0), stearic acid (C18 : 0), oleic

acid (C18 : 1), linoleic acid (C18 : 2), and linolenic acid (C18 :

3). Oleic acid and linoleic acid (64.20–67.42 g/100 g and

15.01–15.82 g/100 g, respectively) were the most abundant

fatty acids found in the rapeseed oils, followed by linolenic

acid (7.82–9.68 g/100 g), palmitic acid (3.31–4.75 g/100 g),

and stearic acid (2.38–2.89 g/100 g). e contents of oleic

acid, linoleic acid, and linolenic acid, which are unsaturated

fatty acids (UFA), and palmitic acid and stearic acid, which

are saturated fatty acids (SFA), were determined. e

contents of saturated and unsaturated fatty acids in rapeseed

oil were 5.69–7.64 g/100 g and 87.03–92.75 g/100 g, respec-

tively. e overall fatty acid prole of rapeseed oils presented

in this work is similar to that reported previously [34]. In this

study, the fatty acid proles of all the oil samples were nearly

indistinguishable, despite the dierent extraction methods

used. However, the statistical analysis showed signicant

dierences between them, particularly the amount of oleic,

linolenic, and linoleic acids, which are the major fatty acids

in these oils. e content of linolenic acid is higher in screw

press in comparison to the hydraulic press and Soxhlet

extraction. In particular, the linolenic acid content of cold-

pressed rapeseed oil extracted by screw press was deter-

mined to be 9.68 g/100 g, which was an increase by 1.50%–

23.80% compared with that of oil in other treatment groups.

Dierent pretreatments had no signicant eect on the fatty

acid composition of rapeseed oil but had a signicant eect

on its content (P <0.05).

High levels of linolenic acid were detected in axseed oils

(47.72–51.01 g/100 g), making them a rich source and de-

livery tool of the essential fatty acid ω-3, followed by oleic

acid (24.33–27.02 g/100 g), linoleic acid (13.49–14.48 g/

100 g), palmitic acid (5.27–5.97 g/100 g), and stearic acid

(4.82–5.16 g/100 g). e total SFA contents were

10.25–10.97 g/100 g, and the total UFA content was

86.57–91.05 g/100 g. e overall fatty acid prole of axseed

oils was similar to that reported previously [35].

e eects of dierent extraction methods on the

composition and content of fatty acids in axseed oil were

the same as those in rapeseed oil. e content of linolenic acid

in cold-pressed axseed oil extracted from a screw press was

the highest, 1.10%–6.90% higher than that in other treatment

groups. In addition, the linoleic acid content of hot-pressed

axseed oil extracted by hydraulic press increased by 4.73% to

11.06% compared with other treatment groups. Teixeira et al.

[36] also used statistical analysis to show a signicant dif-

ference (P <0.05) between fatty acid compositions in samples

extracted by dierent extraction methods.

3.5. Triglycerides. e eects of dierent extraction methods

on composition of triacylglycerols in rapeseed and axseed

oils are shown in Table 3. Some functional properties of oils

depend on not only their fatty acid composition but also the

distribution of the fatty acids at the three positions of the

glycerol backbone. e predominant triglycerides presented

Table 1: Physicochemical properties of rapeseed and axseed oils.

Oil sample Extraction Pretreatment

Acid value (mg KOH/

Peroxide value (meq O

kg)

Saponication value

(mg/g)

Moisture and

volatiles (%)

Rapeseed

oil

Screw press

Hot 0.70 ±0.04

1.16 ±0.00

194.25 ±2.04

0.05 ±0.00

Cold 0.56 ±0.00

0.63 ±0.04

195.87 ±0.75

0.09 ±0.02

Hydraulic press

Hot 0.51 ±0.01

0.52 ±0.01

179.88 ±1.72

0.03 ±0.00

Cold 0.52 ±0.06

0.46 ±0.03

199.88 ±1.11

0.10 ±0.00

Soxhlet

extraction

Hot 3.36 ± 0.18

0.70 ±0.01

173.21 ±1.69

1.54 ±0.01

Cold 1.38 ±0.18

1.45 ±0.07

178.60 ±1.17

0.06 ±0.01

Flaxseed oil

Screw press

Hot 1.01 ±0.00

0.30 ±0.00

183.23 ±0.25

0.10 ±0.03

Cold 1.59 ± 0.07

0.85 ±0.04

197.51 ±0.06

abA

0.15 ±0.01

Hydraulic press

Hot 0.95 ± 0.01

2.31 ±0.01

183.26 ±0.04

0.06 ±0.00

Cold 0.82 ±0.03

0.22 ±0.02

199.43 ±0.63

0.14 ±0.00

Soxhlet

extraction

Hot 1.23 ±0.06

5.23 ±0.25

185.16 ±0.36

1.05 ±0.04

Cold 0.93 ±0.03

0.75 ±0.01

195.28 ±0.21

0.92 ±0.14

Note. Dierent letters in the same column represent signicant dierences (P < 0.05).

6 Journal of Food Quality

Table 2: Fatty acid proles of rapeseed and axseed oils obtained from dierent extraction methods.

Oil sample Extraction methods Pretreatment

Fatty acids (g/100 g)

C16 : 0 C18 : 0 C18 :1 C18 : 2 C18 : 3 SFA UFA

Rapeseed oil

Screw press

Hot 3.55 ±0.06

cdB

2.61 ±0.06

67.42 ±0.03

15.80 ±0.31

9.54 ±0.17

6.16 ±0.12

92.75 ±0.45

Cold 3.66 ±0.01

2.76 ±0.00

67.20 ±0.07

15.68 ±0.05

9.68 ±0.24

6.43 ±0.01

92.56 ±0.37

Hydraulic press

Hot 4.75 ±0.04

2.89 ±0.03

66.11 ±0.45

15.82 ±0.09

9.12 ±0.07

7.64 ±0.07

91.05 ±0.43

Cold 4.29 ±0.00

2.87 ±0.01

64.25 ±0.16

15.73 ±0.18

8.24 ±0.03

7.15 ±0.01

88.22 ±0.37

Soxhlet extraction

Hot 3.31 ±0.00

2.38 ±0.00

64.20 ±0.00

15.01 ±0.01

7.82 ±0.02

5.69 ±0.00

87.03 ±0.01

Cold 3.47 ±0.05

2.51 ±0.04

66.98 ±1.12

15.79 ±0.25

8.29 ±0.14

5.98 ±0.09

91.05 ±1.51

Flaxseed oil

Screw press

Hot 5.39 ±0.18

abB

4.86 ±0.15

24.33 ±0.83

13.49 ±0.44

50.77 ±1.66

10.25 ±0.33

88.59 ±2.92

abB

Cold 5.42 ±0.36

abA

4.96 ±0.33

24.53 ±1.17

13.72 ±0.90

abA

51.01 ±3.25

10.39 ±0.69

abA

89.26 ±5.42

Hydraulic press

Hot 5.27 ±0.01

4.99 ±0.23

25.55 ±0.05

14.48 ±0.37

47.72 ±0.11

10.26 ±0.11

abB

87.75 ±1.60

Cold 5.40 ±0.12

abA

5.16 ±0.04

27.02 ±1.34

abA

14.09 ±0.02

abB

49.33 ±1.65

10.56 ±0.04

abA

90.44 ±1.62

Soxhlet extraction

Hot 5.70 ±0.02

abB

4.82 ±0.00

24.63 ±0.06

13.80 ±0.04

abB

48.14 ±0.96

abB

10.52 ±0.02

abB

86.57 ±0.58

Cold 5.97 ±0.06

5.00 ±0.12

25.80 ±0.19

abA

14.30 ±0.12

abA

50.95 ±0.68

10.97 ±0.18

91.05 ±1.27

Note. Dierent letters in the same column represent signicant dierences (P <0.05).

Journal of Food Quality 7

Table 3: Composition of triacylglycerols in rapeseed and axseed oils.

Oil sample Extraction methods Pretreatment

Triacylglycerols (%)

ECN36 ECN38 ECN40 ECN42 ECN44 ECN46 ECN48 ECN48

LnLnLn LLnLn OLnLn LLL OLL OOL OOO POO

Rapeseed oil

Screw press

Hot 0.46 ±0.01

0.61 ±0.04

2.82 ±0.08

5.48 ±0.03

17.03 ±1.02

21.90 ±0.42

41.93 ±0.11

6.13 ±0.03

Cold 0.40 ±0.23

0.60 ±0.02

2.48 ±0.42

5.35 ±0.16

18.11 ±0.23

22.54 ±0.68

40.82 ±1.80

6.19 ±0.06

Hydraulic press

Hot 0.66 ±0.06

1.11 ±0.52

2.99 ±1.01

6.11 ±0.58

18.78 ±0.50

23.02 ±0.99

37.26 ±2.11

5.90 ±0.24

Cold 0.52 ±0.08

0.95 ±0.08

2.56 ±0.01

6.76 ±0.01

19.16 ±0.04

23.62 ±0.04

39.44 ±0.06

5.82 ±0.01

Soxhlet extraction

Hot 0.43 ±0.11

0.68 ±0.10

2.67 ±0.30

3.98 ±1.87

18.67 ±0.50

22.28 ±0.19

41.20 ±0.57

6.04 ±0.78

Cold 0.46 ±0.07

0.63 ±0.36

2.65 ±0.54

5.34 ±0.10

18.09 ±0.76

22.34 ±0.91

41.94 ±0.56

5.43 ±0.65

Flaxseed oil

Screw press

Hot 16.11 ±0.04

8.05 ±2.14

23.18 ±0.09

13.70 ±0.02

17.62 ±0.08

8.28 ±0.03

6.91 ±0.11

2.42 ±0.09

Cold 16.09 ±0.06

9.53 ±0.01

23.44 ±0.04

13.65 ±0.06

17.74 ±0.03

8.17 ±0.02

6.73 ±0.06

2.34 ±0.01

Hydraulic press

Hot 15.81 ±0.27

9.40 ±0.11

22.39 ±1.35

13.54 ±0.01

17.64 ±0.06

8.85 ±0.13

7.69 ±1.18

2.59 ±0.12

Cold 16.05 ± 0.01

9.48 ±0.00

23.40 ±0.04

13.62 ±0.04

17.65 ±0.04

8.08 ±0.41

6.61 ±0.06

2.32 ±0.12

Soxhlet extraction

Hot 14.74 ±2.08

8.86 ±1.84

21.37 ±2.00

13.20 ±0.05

17.82 ±0.06

9.68 ±1.03

6.34 ±0.54

2.64 ±0.21

Cold 16.16 ±0.06

9.60 ±0.03

23.10 ±0.00

13.66 ±0.02

17.63 ±0.04

8.38 ±0.02

6.96 ±0.02

2.41 ±0.01

Note. Dierent letters in the same column represent signicant dierences (P <0.05).

8 Journal of Food Quality

in rapeseed oil included OOO (37.26%–41.94%), OOL

(21.90%–23.62%), and OLL (17.03–19.16%). e major fatty

acids constituting triglycerides were oleic acid and linoleic

acid. is result is in accordance with the GC analysis of total

fatty acid content in rapeseed oil, in which the compositions

of oleic acid (64.20–67.42 g/100 g) and linoleic acid

(15.01–15.82 g/100 g) were highest (Table 2). Dierent ex-

traction methods had no signicant eect (P > 0.05) on the

compositions and contents of triglycerides. Compared with

blank control, the composition and content of triglyceride in

rapeseed oil were not signicantly aected by roasted pre-

treatment (P >0.05).

Eight types of triglycerides were found in axseed oil:

LnLnLn, LLnLn, OLnLn, LLL, OLL, OOL, OOO, and POO.

Among all these triglycerides, OLnLn (21.37%–23.44%),

OLL (17.62%–17.82%), LnLnLn (14.74%–16.16%), and LLL

(13.20%–13.70%) constituted the main body of triglycerides,

and the sum of their contents exceeded 71% of total content

of triglycerides. is is consistent with the results from fatty

acid determination, in which the content of linolenic acid

(Ln) was found to be highest (47.72–51.01 g/100 g). Dierent

extraction methods and pretreatment had no signicant

eect (P >0.05) on the compositions and contents of tri-

glycerides, which was consistent with the results of rapeseed

oil.

3.6. Volatile Compounds. e eects of dierent extraction

processes on the volatile components of rapeseed and

axseed oils are presented in Table 4. A total of 8 volatile

compounds, aldehydes, acids, alcohols, heterocycles, al-

kanes, esters, ketones, and olens, were identied in the two

types of oils. Aldehydes, acids, alcohols, heterocycles, and

ketones were the main volatile components identied in

rapeseed oils. e contents of alkanes, esters, ketones, and

alkenes were lower than those of other volatile compounds.

Aldehydes mainly impart the fresh, green, grass, and fatty

avors of oils, while heterocycles play a crucial role in their

nutty and roasted avors. In addition, some alcohols (fruity,

coconut) and ketones (oral, fragrant) also contribute to the

avors of oils. Aldehydes are the oxidized products of lipids,

mainly linoleic acids and linolenic acids. Aldehydes were

found to be the dominant volatile compounds accounting

for 1.85%–22.62% of the total amounts of volatiles in the oil

samples. Zhong et al. [37] have determined the volatile

components in cold-pressed camellia oil and reported the

presence of nine saturated aldehydes, from valeraldehyde to

nonanoic acid, in the oil. e volatile components of

rapeseed oils were signicantly aected by dierent ex-

traction methods. In addition, the contents of various vol-

atile components in rapeseed oil are aected by roast

pretreatment. e contents of acids, aldehydes, and alcohols

in cold-pressed rapeseed oil extraction by the hydraulic press

were the highest, which were 2.33–6.53, 1.34–3.47, and

1.41–4.2 times those in other treatment groups, respectively.

e contents of heterocycles and ketones compounds in hot-

pressed rapeseed oil extraction from screw press were, re-

spectively, 1.30–3.00 and 1.34–3.37 times higher than those

in other treatment groups.

e major volatile compounds in axseed oils are acids

(5.36%–32.27%), aldehydes (1.97%–34.77%), heterocycles

(7.26%–46.79%), alcohols (3.51%–29.53%), and ketones

(2.18%–20.76%). Dierent oil preparation processes and

pretreatment aected the contents of volatile compounds in

axseed oils. Compared to other ndings, Danh et al. [38]

have also revealed that the volatile components of the lav-

ender essential oils exhibit considerable variations among

the extraction methods.

Acids accounted for 5.36%–32.27% of total volatiles in

axseed oils; however, they have a relatively high

threshold value and do not signicantly contribute to the

odor of vegetable oils. erefore, the aroma of oils ob-

tained by the experiment is mainly due to only several

volatile components. e content of aldehydes in axseed

oils extraction from screw press was the highest, which

was 1.70–17.65 and 1.70–3.50 times those of hydraulic

press and Soxhlet extraction, respectively. Alcohols have

aromatic, vegetative, rancid, and earthy avors. Alcohols

were detected mainly in the cold-pressed axseed oil

obtained from hydraulic press method, which were

3.00–8.40 times higher than those in other treatment

groups. Heterocyclic substances are the products of the

Maillard reaction, which mainly include pyrazine, furan,

pyrrole, pyrimidine, and thiazole. High protein oilseeds

are the basic materials for the Maillard reaction. As can be

seen from Table 4, the contents of heterocyclic substances

in axseed oil samples extracted using screw press and

hydraulic press methods were higher than those in oil

samples extracted using Soxhlet extraction. In particular,

the contents of heterocyclic substances in hot-pressed

axseed oil extraction by the hydraulic press were the

highest, 2.50–6.50 times higher than those in other

treatment groups.

3.7. Total Phenol Content and Vitamin E. Total phenol and

vitamin E contents of rapeseed and axseed oils extracted

using dierent methods are presented in Figure 3. e total

phenolic contents in rapeseed and axseed oils were

102.66–191.67 μg/g and 120.16–147.83 μg/g, respectively.

e contents of vitamin E in rapeseed oil

(474.70–849.30 mg/kg) were signicantly higher than those

in axseed oil (330.30–424.90 mg/kg).

Furthermore, the total phenol contents of the two types

of oils prepared by Soxhlet extraction method were the

highest. e total phenol contents in hot-pressed oils were

higher than those of cold-pressed oils, which was consistent

with the work of Wang et al. [39] on the steam explosion

pretreatment of rapeseed. In particular, the total phenol

contents of hot-pressed rapeseed oil and axseed oil

extracted by Soxhlet extraction increased by 21.88%–68.10%

and 1.11%–23.03%, respectively, compared to other

methods. is may be due to the fact that the extraction time

of the Soxhlet extraction method was 8 h, which was 12–60

times longer than that of other methods. Moreover, the

Soxhlet extraction was continuously repeated using a con-

densed pure solvent; as a result, the total phenol content was

the highest. ese results indicate that dierent extraction

Journal of Food Quality 9

processes signicantly aected the total phenol contents in

the two types of oils.

e vitamin E contents in the two types of oils were also

signicantly dierent and were aected by other extraction

processes. e vitamin E content of rapeseed oil is ∼2 times

that of axseed oil. e vitamin E content of rapeseed oil and

axseed oil produced by screw press was higher than that of

the hydraulic press and Soxhlet extraction. In addition,

the contents of vitamin E in cold-pressed rapeseed oil

and axseed oil obtained by screw press increased by

1.22%–78.91% and 3.00%–18.80%, respectively, compared to

other methods. Compared with screw press, the vitamin E

loss rates of the two oils obtained by hydraulic press and

Soxhlet extraction were 14.00%–41.00% and 4.00%–44.00%,

respectively. In general, the vitamin E content of the oil can

be increased by screw press.

4. Conclusion

e mechanical press was considered superior to the Soxhlet

extraction method in terms of sensory score and physico-

chemical indexes (acid value, peroxide value, saponication

Hot pressed of screw

Hot pressed of hydraulic

Cold pressed of soxhlet

Cold pressed of hydraulic

Cold pressed of screw

Hot pressed of soxhlet

100

120

140

160

180

200

Total phenols (µg/g)

Rapeseed oil

Flaxseed oil

(a)

200

400

600

800

1000

Vitamin E (mg/kg)

Hot pressed of screw

Hot pressed of hydraulic

Cold pressed of soxhlet

Cold pressed of hydraulic

Cold pressed of screw

Hot pressed of soxhlet

Rapeseed oil

Flaxseed oil

(b)

Figure 3: Total phenol and vitamin E contents in rapeseed and axseed oils. (a) Total phenol. (b) Vitamin E.

Table 4: SPME-GCMS analysis of volatile compounds in rapeseed and axseed oils.

Oil sample

Extraction

methods

Pretreatment

Volatile compounds (%)

Acids Aldehydes Heterocycles Alcohols Alkanes Esters Ketones Alkenes Other

Rapeseed oil

Screw press

Hot 10.77 1.85 23.9 16.01 0.5 1.38 13.45 1.87 30.27

Cold 17.75 15.12 11.12 13.03 0.87 1.63 3.99 1.58 34.91

Hydraulic press

Hot 11.99 6.52 18.43 5.79 1.52 3.96 10.05 4.3 37.44

Cold 43.22 22.62 — 18.29 3.26 — 12.6 — 0.01

Soxhlet extraction

Hot 18.53 13.52 12.97 4.35 7.56 0.37 7.81 18.57 16.32

Cold 6.62 16.83 7.96 8.18 10.12 4.2 7.78 4.44 33.87

Flaxseed oil

Screw press

Hot 32.27 34.77 12.06 9.5 2.92 3.32 2.68 — 2.48

Cold 31.24 26.38 18.82 6.19 1.39 1.99 5.24 — 8.75

Hydraulic press

Hot 5.36 1.97 46.79 4.69 1.2 3.75 2.18 31.52 2.54

Cold 25.48 15.46 10.58 29.53 — — 15.02 — 3.93

Soxhlet extraction

Hot 21.62 9.94 10.17 3.51 7.31 5.81 20.76 3.18 17.7

Cold 20.72 15.65 7.26 10.12 8.8 2.05 13.55 2.32 19.53

Note. —: less than 0.5% or undetectable.

10 Journal of Food Quality

value, moisture, and volatiles). e physicochemical indexes

of oil extracted by the screw press method were comparable

to those of oil extracted by the hydraulic press. e contents

of vitamin E in cold-pressed rapeseed and axseed oils

obtained by screw press increased by 1.22%–78.91% and

3.00%–18.80%, respectively, compared to other methods. By

contrast, the total phenol contents of hot-pressed rapeseed

and axseed oils extracted by Soxhlet extraction increased by

21.88%–68.10% and 1.11%–23.03%, respectively, compared

to other methods, and the oil yields increased by 30.10%–

73.90% and 6.30%–54.40%, respectively. Nonetheless, the

quality of the oil was inferior due to high acid value

(0.93–3.36 mg KOH/g), peroxide value (0.70–5.23 meq O

kg), and moisture and volatile contents (0.06%–1.54%), and

the possibility of using the defatted our is limited to the

presence of a residual solvent. In addition, the proles of

fatty acids obtained from dierent extraction methods and

pretreatment were similar, but the statistical analysis showed

that the proles diered signicantly. In particular, the

linolenic acid contents of cold-pressed rapeseed and axseed

oils extracted by screw press were determined to be 9.68 g/

100 g and 51.01 g/100 g, respectively, which increased by

1.50%–23.80% and 1.10%–6.90% compared with other

treatments, respectively. Dierent extraction methods did

not aect the composition and content of triglycerides in the

two types of oils. Aldehydes, acids, alcohols, heterocycles,

and ketones were the main volatile components in both

types of oils. Dierent extraction methods also aected the

volatile components of rapeseed and axseed oils.

Data Availability

e data used to support the ndings of this study are in-

cluded within the article.

Conflicts of Interest

e authors declare no conicts of interest.

Authors’ Contributions

Shuzhen Wang contributed to methodology, formal anal-

ysis, data curation, and review and editing. Jinying Wang

contributed to conceptualization, resources, methodology,

supervision, and writing of the original draft, review and

editing, and project administration. Guoxin Dong con-

tributed to formal analysis and review and editing. Xia Chen

contributed to methodology and supervision. Shulin Wang

contributed to formal analysis and supervision. Feng lei

contributed to data curation and review and editing.

Xuebing Su contributed to provision of resources and su-

pervision. Qin Bai contributed to provision of resources and

investigation.

Acknowledgments

is work was supported by the Science and Technology

Department of Qinghai Province, Qinghai Enterprise

Research Transformation and Industrialization Special

Project (Grant no. 2021-NK-C19).

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Hindawi Journal of Food Quality
Volume 2022, Article ID 8296212, 12 pages
https://doi.org/10.1155/2022/8296212 Research Article
Effect of Different Extraction Methods on Quality
Characteristics of Rapeseed and Flaxseed Oils
Shuzhen Wang ,1 Jinying Wang ,1,2 Guoxin Dong ,1 Xia Chen ,1 Shulin Wang ,1
Feng Lei ,1 Xuebing Su ,3 and Qin Bai 3
1College of Agriculture and Animal Husbandry, Qinghai University, Xining 810016, China
2State Key Laboratory of Plateau Ecology and Agriculture, Qinghai University, Xining 810016, China
3Qinghai Tongda Oil Processing Co. Limited, Haidong 810600, China
Correspondence should be addressed to Jinying Wang; wangjinying0128@126.com
Received 25 May 2022; Revised 11 August 2022; Accepted 29 August 2022; Published 19 September 2022
Academic Editor: Vita Di Stefano
Copyright © 2022 Shuzhen Wang et al. .is is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
.is study reports the eﬀect of roasted pretreatment combined with screw press, hydraulic press, and Soxhlet extraction methods
on various quality indexes of rapeseed and ﬂaxseed oils, including the oil yield, sensory indexes (color, smell, clarity, viscosity, and
colligation score), physicochemical properties (acid value, peroxide value, saponiﬁcation value, moisture and volatiles), major
components (fatty acid composition and triglyceride composition), and minor components (volatile compounds, total phenols,
and vitamin E contents). .e results indicated that the oil yield, sensory indexes, physicochemical properties, fatty acid
composition, volatile compounds, total phenol, and vitamin E contents in vegetable oils have been signiﬁcantly aﬀected by
diﬀerent extraction methods. .e yields of rapeseed and ﬂaxseed oils of Soxhlet extraction method were increased by 30.10%–
73.90% and 6.30%–54.40%, respectively, compared with other treatment groups. In addition, roasted pretreatment signiﬁcantly
increased the yields of oils by 4.10%–25.00% and 6.70%–23.15%, respectively, compared with the untreated group. .e contents of
linolenic acid and vitamin E in rapeseed and ﬂaxseed oils extracted from screw press method were higher. In particular, the
linolenic acid content of cold-pressed rapeseed oil extracted by screw press increased by 1.50%–23.80% compared with other
treatment groups. In addition, the contents of vitamin E in cold-pressed rapeseed oil and ﬂaxseed oil obtained by screw press
increased by 1.22%–78.91% and 3.00%–18.80%, respectively. .e Soxhlet extraction could improve oil yield and total phenol
content, but the quality of the oil was inferior due to high acid values (0.93–3.36 mg KOH/g) and peroxide values (0.70–5.23 meq
O2/kg). Furthermore, the hydraulic press method could extract vegetable oils with excellent sensory scores. .e roasted pre-
treatment gives the rapeseed and ﬂaxseed oils a good smell. .e major volatile compounds in rapeseed and ﬂaxseed oils were
aldehydes, acids, alcohols, heterocycles, and ketones. Diﬀerent extraction methods and pretreatment had no signiﬁcant eﬀect on
the compositions and contents of triglycerides. .is study provides a basic understanding on the selection of appropriate oil
extraction techniques for oil extraction at a large scale. 1. Introduction
micronutrients including antioxidant vitamins such as vi-
tamin E [4], polyphenols such as sinapic acid (free phenolic
Rapeseed is one of the major edible vegetable oil seeds with
acid), sinapine (esteriﬁed form; the most abundant species)
high oil contents (38%–50%) [1]. Canada and China are the
[5], and phytosterols [6], which have strong antioxidant,
top two producers of rapeseeds worldwide, and rapeseed oil
senility-delaying, and antihypercholesterolemic activities
is mainly consumed in China [2]. As the traditional bulk
[7]. In particular, vitamin E oﬀers protection against oxi-
edible oil in China, natural rapeseed oil is rich in omega-3
dative deterioration and maintains the sensory properties of
polyunsaturated fatty acids, and the dominant type is foods [8].
linolenic acid, which represents ∼8% of total fatty acids [3].
Oilseed ﬂax (Linum usitatissimum L.) is one of the most Rapeseed oil also contains many cardioprotective
important oil crops in the alpine regions of North and
6095, 2022, 1, Downloaded from https://onlinelibrary.wiley.com/doi/10.1155/2022/8296212 by Readcube (Labtiva Inc.), Wiley Online Library on [16/12/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License 2 Journal of Food Quality
Northwest China [9]. As an ancient edible vegetable oil,
processors to select the extraction methods that result in
ﬂaxseed oil contains an abundant omega-3 fatty acids and the optimal oil quality.
small amounts of other components such as polyphenols
and phytosterols. Omega-3 fatty acids have been reported to
2. Materials and Methods
be associated with a lower risk of cardiovascular disease [10],
diabetes [11], and cancer [12].
2.1. Samples and Chemicals
Oil extraction methods play an important role in veg-
etable oil yields, qualities, and oxidation stability. .ere are
2.1.1. Samples. Rapeseeds “Qingza No. 12” and ﬂaxseeds
many technical processes involved in the extraction of oils
“Dingya No. 18” were collected from the Xining and Guide
from the same origin, making the ﬁnal products diﬀerent in
in Qinghai (harvest date: March 2021). .e seeds were stored
physicochemical proprieties and nutritional values [13, 14]. at 4°C until extraction.
In China, there are many traditional extraction methods,
such as solvent extraction and mechanical pressing. Screw
2.1.2. Reagents. Chromatographic-grade n-heptane and
press is one of the oldest and most popular methods for oil
methanol were purchased from Damao Chemical Reagents
production worldwide [15] because the technique is easy to
Co. (Tianjin, China). Methyl undecanoate, methyl hex-
operate and maintain. However, the method could only
adecanoate, methyl stearate, methyl oleate, methyl linoleate,
partially defat the seeds. .erefore, the resulting press cake
and methyl linolenate were purchased from Sigma Aldrich
must be defatted by percolation with hexane. Another Trading Co. (Shanghai, China).
mechanical pressing method is the hydraulic press method,
which is also one of the oldest and simplest methods for oil
extraction. Although the hydraulic press method results in a 2.2. Oil Extraction
lower oil yield than the solvent extraction method, the
2.2.1. Sample Pretreatment. Seeds were cleaned and sieved
method gives oil higher quality. One study has reported that
to remove debris. .e whole seeds are roasted in an elec-
oils extracted with the hydraulic press tend to contain a
tromagnetic oven, the roasted temperature is 160°C–180°C,
higher content of phytosterols [16]. Solvent extraction is one
the time is 10 min, and the seeds are constantly turned
of the cheapest and most eﬃcient techniques for producing
during the roasting to avoid burning. Untreated seeds were
edible oils [17], such as Jojoba oil, soybean oil, palm oil, and
used as controls, which represent the cold application.
jatropha oil. In the solvent extraction method, oil seeds are
pretreated (grind) and then placed in a suitable solvent to
extract the oil from the solid matrix to the liquid phase.
2.2.2. Screw Press. Vegetable oil was extracted using an XZ-
Zanqui et al. [18] showed that the average oil yield of ﬂaxseed
Z505W horizontal screw press machine (Guangzhou Xuz-
oil extracted by the subcritical n-propane ﬂuid extraction
hong Food Machinery Co., LTD, China). .e output of the
(SubFE) method was 28%, and it had higher purity and
screw press was 0.36 t/h. Gravity fed samples at the hopper of higher oxidation stability.
the screw press, and the oil was collected at the outlet. .e
Because it is diﬃcult to extract all of the oil contents from
temperatures of the screw press were 160°C–180°C. Oil
seeds, particularly by mechanical methods, it can be bene-
temperature was 40°C. To slow down oil oxidation and
ﬁcial to develop a pretreatment method that generates oil
remove some impurities, after centrifugation at 2500g for
with a high yield from oilseeds while maintaining the nu-
15 min, the oil samples were kept in a 250 mL brown bottle
tritional and quality characteristics. Researchers have re-
and stored in a refrigerator at 4°C until further analysis.
cently studied several pretreatments for improving oil yields,
such as roasted, freeze-thaw, microwave irradiation [19] and
2.2.3. Hydraulic Press. Oilseed ﬂakes were packed in a cloth
dielectric [20] and ultrasound-assisted hexane extraction.
sheet and placed in a metallic pressing cylinder. .e raw
Roasting is a pretreatment method of oilseeds which can
material capacity of the hydraulic press is 3–6 kg. .e oilseed
provide signiﬁcant beneﬁts to seeds used for consumption
ﬂakes inside the metallic cylinder were then preheated at
and oil extraction. .is method promotes some desirable or
60°C–70°C. While heating, the metallic cylinder was pressed
undesirable changes in chemical, physical, and nutritional
using an XZ-Z505W hydraulic press machine (Guangzhou
characteristics [21, 22]. Roasting seeds before oil extraction
Xuzhong Food Machinery Co., LTD, China). At a pressure
has been shown to have a signiﬁcant impact on oil as it helps
of 50 MPa for 15 min, oil temperature was 50°C. After that,
to generate a distinctive aroma and improve the oxidative
the oil was centrifuged at 2500g for 15 minutes and then
stability of the oil due to by-products formed as a result of
stored in a 250 mL brown bottle at 4°C until subsequent the Maillard reaction [23]. analysis.
.e main objective of this study is to compare the
eﬀects of diﬀerent extraction methods, including screw
press, hydraulic press, and Soxhlet extraction methods, on
2.2.4. Soxhlet Extraction. Vegetable oil was extracted from
the quality of rapeseed and ﬂaxseed oils. .e major
these samples with a SOX406 fat analyzer (Shandong Hai-
components (fatty acid composition and triglyceride
neng Scientiﬁc Instrument Company, China). In a typical
composition) and minor components (volatile compo-
extraction, ground dried seeds (6 g) were packed in a thimble
nents, vitamin E, and total phenol contents) were analyzed
and then extracted with petroleum ether (100 mL). .e
to assess the quality of oils. .is study provides data for
immersion, washing, and recovery steps were performed at
6095, 2022, 1, Downloaded from https://onlinelibrary.wiley.com/doi/10.1155/2022/8296212 by Readcube (Labtiva Inc.), Wiley Online Library on [16/12/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License Journal of Food Quality 3
70°C, and each step lasted for 2, 5, and 1 h, respectively. All
subjecting to high-performance liquid chromatographic
the extracted oils were collected, and the residual solvent was analysis.
removed using a draught drying cabinet. .e oil was stored
(2) HPLC-ELSD Analysis. Triglycerides were analyzed
in 250 mL brown bottle at 4°C until further analysis.
using a LC-20AD high-performance liquid chromatograph
(HPLC) (Shimadzu, Tokyo, Japan) equipped with an
evaporative light-scattering detector (ELSD) and a C18 2.3. Analytical Methods
column (5.0 μm, 4.6 × 250 mm). .e column temperature
was set at 40°C, and the detector temperature was set to 30°C.
2.3.1. Sensory Analysis. Oil sensory analysis was carried out
Sample at a volume of 5 μL was injected into the HPLC and
according to Szydłowska-Czerniak et al. [24]. Fifteen pro-
then eluted with acetonitrile : isopropanol (30 : 70, v/v) at a
fessional evaluators were employed to evaluate the color, ﬂow rate of 0.5 mL/min.
smell, clarity, viscosity, and colligation score of the samples.
(3) Qualitative and Quantitative Analysis. Based on their
.e samples were given scores on a 5-point scale ranging
ECN partitioning, which occurs in the same order as the
from 0 (extremely low) to 5 (extremely high).
number of carbon atoms in ECN (from small to large), each
triglyceride was qualitatively analyzed based on the order in
2.3.2. Physicochemical Properties. Standard methods of the
which the peak emerged. .e area normalization method
International Organization for Standardization (ISO) were
was used for quantitative analysis.
used to determine the acid value (ISO 660, 2020), peroxide
value (ISO 3960, 2017), saponiﬁcation value (ISO 3657,
2020), and moisture and volatiles contents (ISO 665, 2020).
2.3.5. Volatile Compounds. Volatile compounds were de-
termined by reference to the method of Ojeda-Amador et al.
with minor modiﬁcations [27].
2.3.3. Fatty Acid Proﬁle. Fatty acid contents were deter-
(1) Solid-Phase Microextraction (SPME). Solid-phase
mined according to laboratory-established methods [25].
microextraction (SPME) was performed using a 50/30 μm
(1) Sample Preparation. 100 ± 0.1 mg of oil samples,
PDMS/DVB/CAR PK3 ﬁber (Beijing, China). 6 ± 0.1 g of oil
40 mL of methanol, 1 mL of potassium hydroxide methanol
was transferred into a 15 mL glass vial, which was then
(1 mol/L), and 0.5 mL of methyl undecanoate (10 mg/mL;
inserted with a microstirring bar. .e vial was placed in a
internal standard solution) were mixed until homogenous,
magnetic water bath at 80°C and stirred magnetically. After
and the mixture solution was then shaken in water bath at
allowing the sample to equilibrate for 20 min, the needle of
50°C for 60 min until the solution was clear. .en, the ester
the SPME device was inserted into the vial, and the ﬁber was
layer was extracted using n-heptane. .e FAME solutions
allowed to expose to the headspace of the sample. After
were diluted with n-heptane prior to injection into the GC
40 min of exposure, the ﬁber was retracted from the vial column.
headspace and then inserted into the gas chromatograph
(2) GC-FID Analysis. .e prepared samples were injector.
autoinjected into a Shimadzu GC-2030 gas chromatograph
(2) GC-MS Analysis. An QP2020 NX series gas chro-
(Shimadzu, Japan) equipped with a fused silica Wonda Cap
matograph-mass spectrometer (Shimadzu, Japan) was used WAX column (60 m in length × 250 μm in
to analyze volatile compounds adsorbed on the SPME ﬁber.
diameter × 0.25 μm). .e injector and detector temperatures
.e separation was carried on an InertCap-wax column
were ﬁxed at 250°C. High-purity hydrogen was used as the
(30 m × 0.25 mm, 0.25 μm). Helium was used as the carrier
carrier gas ﬂowing at a ﬂow rate of 1 mL/min. .e injection
gas ﬂowing at a ﬂow rate of 1.0 mL/min. .e injector was
volume was 1 μL, and the injection was carried out at a split
operated at 250°C in a split mode at split ratio of 50 : 1. .e
ratio of 46 : 1. .e column temperatures were programmed
SPME ﬁber was kept in the injector for 5 min. .e column
as follows: initial oven temperature was set at 100°C and held
was maintained at a temperature of 40°C for 2 min; after that,
for 13 min; raised to 180°C at 10°C/min and held for 6 min;
it was heated to 220°C at a rate of 5°C/min and held for
raised to 200°C at 1°C/min and held for 20 min; and ﬁnally
10 min. .e MS conditions were as follows: source tem-
raised to 230°C at 4°C/min and held for 10.5 min.
perature, 150°C; transfer line temperature, 260°C; acquisi-
(3) Qualitative and Quantitative Analysis. Qualitative
tion mode, electron impact (EI 70 eV) at 3 scans per second;
analysis of fatty acids was carried out based on the retention
and mass range, 235–350 m/z.
time of 5 types of fatty acid methyl esters, and quantitative
(3) Qualitative and Quantitative Analysis. In qualitative
analysis was conducted using the internal standard method.
analysis, the spectra of the compounds were searched against
the NIST 14 standard spectrum library and compared with
those of the standard. .e area normalization method was
2.3.4. Triglyceride Proﬁle. Triglyceride contents were de- used in quantitative analysis.
termined according to laboratory established methods [26].
(1) Sample Preparation. 1 ± 0.1 g of oil was mixed with the
mobile phase (acetonitrile : isopropanol (30 : 70, v/v)) in a
2.3.6. Total Phenols. Total phenols content was estimated by
10 mL volumetric ﬂask. After swirling for 1 min until
the Folin-Ciocalteu colorimetric method, based on the
completely mixed, the mixture was ﬁltered through a
procedure of Suri et al. [28], using gallic acid as a standard
0.45 um nylon ﬁlter membrane in an injection ﬂask before phenolic compound.
6095, 2022, 1, Downloaded from https://onlinelibrary.wiley.com/doi/10.1155/2022/8296212 by Readcube (Labtiva Inc.), Wiley Online Library on [16/12/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License 4 Journal of Food Quality
(1) Sample Preparation. Oil sample was weighed to
(OriginLab, USA). All results were expressed as arithmetic
0.5 ± 0.1 g and then subjected to extraction with 2.5 mL of
means of three independent measurements ± standard de-
70% methanol solution. After 5 min, the sample was viations (SDs).
ultrasonicated for 5 min, refrigerated for 5 min, and then
centrifuged for 5 min at 2500g, and the supernatant was
3. Results and Discussion
transferred to a 10 mL volumetric ﬂask. .e above process
was repeated 3 times, and the volume was ﬁxed with 70%
3.1. Oil Extractions. Figure 1 shows the eﬀect of diﬀerent oil
methanol solution. In another 10 mL volumetric ﬂask, 1 mL
extraction methods on rapeseed and ﬂaxseed oil yield.
of extraction solution, 1 mL of diluted Folin-Ciocalteu (FC)
Figure 1(a) shows that the rapeseed oil yield extraction by
reagent, and 3 mL of 10% sodium carbonate solution were,
the Soxhlet extraction method is the highest, which is
respectively, added. Pure water was added for volume
39.10%–40.70%, while the rapeseed oil yields of screw press
measurement and then let stand in darkness for 2 h.
and hydraulic press method are 24.00%–30.00% and
(2) Qualitative and Quantitative Analysis. .e absor-
23.40%–26.20%, respectively. .e yield of the hot-pressed
bance at 765 nm was measured using a UV-1780 spectro-
treatment group was higher than that of the cold-pressed
photometer (Shimadzu, Japan). .e total phenol content
treatment group, which indicated that roasted pretreatment
was calculated by the equation obtained from the standard
could increase the rapeseed oil yield. .is may be because curve of gallic acid, which was:
Y � 0.0799X +
roasted pretreatment destroys the cellular structure of the
0.0368 R2 � 0.9981.
seeds, making the oils easier to extract [30]. Diﬀerent oil
extraction methods and pretreatment had signiﬁcant eﬀects
on rapeseed oil yield (P < 0.05); the yield of rapeseed oil
2.3.7. Vitamin E. Vitamin E was measured based on Faghim
prepared by the Soxhlet extraction method increased by
et al.’s method with slight modiﬁcations [29].
30.10%–73.90% compared with other methods. .e yield of (1) Sample Preparation. Sample was accurately
rapeseed oil in hot-pressed treatment increased by 4.10% to
(Y � 0.0799X + 0.0368 R2 � 0.9981) weighed to 1.5 ± 0.1 g
25.00% compared with that in cold-pressed treatment.
and then placed in a 50 mL brown centrifuge tube. After 0.2 mL
Figure 1(b) shows that the yield of ﬂaxseed oil obtained
of 50% potassium hydroxide, 0.6 mL of anhydrous ethanol, and
by diﬀerent oil extraction methods is Soxhlet extraction
0.2 mL of 16 g/L pyrogallic acid were added, the tube was (31.88%–34.50%) > screw press (24.36%–30.00%)
shaken for 1 min. Saponiﬁcation was carried out in a water bath
> hydraulic press (22.34%–23.84%). .e Soxhlet extraction
at 80°C for 30 min in darkness. After the reaction was complete,
method has the highest yield of ﬂaxseed oil, but its appli-
the tube was cooled down to room temperature in cold water.
cation in the food industry is limited due to the presence of
Five milliliters of petroleum ether was added to the saponiﬁ-
organic solvent residue in the oil. In contrast, the yield of
cation reaction solution, and the mixture was vigorously mixed
ﬂaxseed oil extracted by screw press was 8.07%–34.28%
by oscillation for 1 min; after that, it was let stand for 15 min.
higher than that of hydraulic press, which was more suitable
.e petroleum ether layer was transferred into another 50 mL
for producing ﬂaxseed oil. Diﬀerent pretreatments had
brown centrifuge tube. .e extraction step was repeated using
signiﬁcant eﬀects on the yield of ﬂaxseed oil, and the yield of
5 mL and 3 mL of petroleum ether. .e three extracts were then
cold-pressed ﬂaxseed oil was 6.70%–23.15% lower than that
combined and dried under nitrogen stream at room tem- of hot-pressed ﬂaxseed oil.
perature. .e dried sample was redissolved in 0.2 mL of
chromatography-grade methanol, ﬁltered through a 0.22 μm
membrane, and then immediately subjected to analysis.
3.2. Sensory Quality. .e sensory quality of rapeseed and
(2) HPLC-DAD Analysis. .e content of vitamin E in oil
ﬂaxseed oils prepared by diﬀerent oil extraction methods
samples was analyzed by 1100-VWD HPLC equipped
was evaluated based on various indicators including color,
(Agilent, China) with a photodiode array detector, of which
smell, clarity, viscosity, and colligation score, and the results
the emission wavelength was set at 300 nm. .e injection
are shown in Figure 2. As illustrated in Figure 2(a), the
volume was 10 μL. .e separation was carried out using a
sensory scores of rapeseed oil extracted by hydraulic press
.ermo Scientiﬁc Syncronis HPLC column with dimensions
were highest, followed by those of oil extracted by screw
of 250 mm × 4.6 mm. .e ﬂow rate was set at 1.3 mL/min.
press and Soxhlet extraction. Additionally, hot-pressed
Methanol and water at a ratio of 92/8 (v/v) were used as the
rapeseed oil had a better smell, while cold-pressed oil had mobile phase. better color and clarity.
(3) Qualitative and Quantitative Analysis. Qualitative
.e sensory quality of ﬂaxseed oil was similar to that of
analysis was carried out using vitamin E standard, and
rapeseed oil. In particular, hot-pressed ﬂaxseed oil had a
quantitative analysis was conducted using the standard curve,
better smell than cold-pressed ﬂaxseed oil. .is indicates
of which the equation was Y � 1.3901X + 0.1644 R2 � 0.999.
that using roasting as a pretreatment step for rapeseed oil
and ﬂaxseed oil extraction could increase consumer satis-
2.4. Statistical Analysis. .e data was statically analyzed
faction. .is is consistent with research by Yin et al. [31]
using SPSS 26.0 (IBM, USA). To identify signiﬁcant dif-
which showed that consumers prefer roasted sesame oil to
ferences among the extraction methods, two-way analysis of
cold-pressed sesame oil. Based on the sensory quality, hy-
variance (ANOVA) was performed at 95% signiﬁcance level
draulic press is the most suitable method for extracting oils
(a � 0.05). Graphs were prepared using Origin 2018 from rapeseed and ﬂaxseed.
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Screw press Hydraulic press Soxhlet extraction
Screw press Hydraulic press Soxhlet extraction Oil sample Oil sample Hot Hot Cold Cold (a) (b)
Figure 1: Oil yield of rapeseed and ﬂaxseed oils extracted by diﬀerent extraction methods. (a) Rapeseed oil and (b) ﬂaxseed oil. ** ** Color Color 5 5 4 4 3 3 Colligation 2 Colligation score Smell 2 Smell score ** 1 ** ** ** 1 0 0 Viscosity Clarity ** ** Viscosity Clarity ** ** Hot pressed of screw Hot pressed of hydraulic Hot pressed of screw Hot pressed of soxhlet Hot pressed of hydraulic Cold pressed of screw Hot pressed of soxhlet Cold pressed of hydraulic Cold pressed of screw Cold pressed of soxhlet Cold pressed of hydraulic Cold pressed of soxhlet (a) (b)
Figure 2: Sensory scores of rapeseed oil and ﬂaxseed oil extracted by diﬀerent extraction methods. (a) Rapeseed oil and (b) ﬂaxseed oil. 3.3. Physicochemical Properties. .e physicochemical
.e highest acid and moisture values were determined in
properties of oils extracted from oilseeds using diﬀerent
Soxhlet extraction in hot rapeseed oil. .e highest per-
extraction methods are shown in Table 1. Acid values of
oxide value was determined in Soxhlet extraction in hot
the extracted rapeseed and ﬂaxseed oils were 0.51–3.36 mg
ﬂaxseed oil. In particular, the acid values of hot-pressed
KOH/g and 0.82–1.59 mg KOH/g, respectively, and their
rapeseed oil extracted by Soxhlet extraction were
peroxide values were between 0.22 and 5.23 meq O2/kg.
2.11∼6.58 times those of other treatments. .is might be
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Table 1: Physicochemical properties of rapeseed and ﬂaxseed oils.
Acid value (mg KOH/ Peroxide value (meq O Saponiﬁcation value Moisture and Oil sample Extraction Pretreatment 2/ g) kg) (mg/g) volatiles (%) Hot 0.70 ± 0.04cA 1.16 ± 0.00bA 194.25 ± 2.04cB 0.05 ± 0.00cB Screw press Cold 0.56 ± 0.00dB 0.63 ± 0.04dB 195.87 ± 0.75bA 0.09 ± 0.02bA Rapeseed Hot 0.51 ± 0.01eB 0.52 ± 0.01eA 179.88 ± 1.72dB 0.03 ± 0.00cB Hydraulic press oil Cold 0.52 ± 0.06eA 0.46 ± 0.03fB 199.88 ± 1.11aA 0.10 ± 0.00bA Soxhlet Hot 3.36 ± 0.18aA 0.70 ± 0.01cB 173.21 ± 1.69fB 1.54 ± 0.01aA extraction Cold 1.38 ± 0.18bB 1.45 ± 0.07aA 178.60 ± 1.17eA 0.06 ± 0.01dB Hot 1.01 ± 0.00cB 0.30 ± 0.00dB 183.23 ± 0.25cB 0.10 ± 0.03cB Screw press Cold 1.59 ± 0.07aA 0.85 ± 0.04cA 197.51 ± 0.06abA 0.15 ± 0.01cA Hot 0.95 ± 0.01cA 2.31 ± 0.01bA 183.26 ± 0.04cB 0.06 ± 0.00cB Flaxseed oil Hydraulic press Cold 0.82 ± 0.03dB 0.22 ± 0.02dB 199.43 ± 0.63aA 0.14 ± 0.00cA Soxhlet Hot 1.23 ± 0.06bA 5.23 ± 0.25aA 185.16 ± 0.36cB 1.05 ± 0.04aA extraction Cold 0.93 ± 0.03cB 0.75 ± 0.01cB 195.28 ± 0.21bA 0.92 ± 0.14bB
Note. Diﬀerent letters in the same column represent signiﬁcant diﬀerences (P < 0.05).
because the oil’s water content was too high, which was
study, the fatty acid proﬁles of all the oil samples were nearly 1.54%.
indistinguishable, despite the diﬀerent extraction methods
Moreover, with the increase of temperature, the hy-
used. However, the statistical analysis showed signiﬁcant
drolysis reaction of oil accelerated; thus, the acid value
diﬀerences between them, particularly the amount of oleic,
increased. .e peroxide value of hot-pressed ﬂaxseed oil
linolenic, and linoleic acids, which are the major fatty acids
extracted by Soxhlet extraction was determined to be
in these oils. .e content of linolenic acid is higher in screw
5.23 meq O2/kg, which was an increase of 1.26%–22.77%
press in comparison to the hydraulic press and Soxhlet
compared with that of oil in other treatment groups. .e rise
extraction. In particular, the linolenic acid content of cold-
in the peroxide values of rapeseed and ﬂaxseed oils obtained
pressed rapeseed oil extracted by screw press was deter-
from the Soxhlet extraction system may be attributed to the
mined to be 9.68 g/100 g, which was an increase by 1.50%–
solvent used, the applied heat, and the presence of oxygen in
23.80% compared with that of oil in other treatment groups.
the system [32]. Similar results were reported for ﬂaxseed
Diﬀerent pretreatments had no signiﬁcant eﬀect on the fatty
oils. Kulkarni et al. [33] observed that oil extracted by
acid composition of rapeseed oil but had a signiﬁcant eﬀect
Soxhlet method had the highest peroxide value, whereas the
on its content (P < 0.05).
peroxide value of commercial screw press expeller was the
High levels of linolenic acid were detected in ﬂaxseed oils
lowest. .e saponiﬁcation values of rapeseed and ﬂaxseed
(47.72–51.01 g/100 g), making them a rich source and de-
oils extracted by diﬀerent methods were found to be between
livery tool of the essential fatty acid ω-3, followed by oleic
173.21 and 199.88 mg/g; these values reﬂect not only the
acid (24.33–27.02 g/100 g), linoleic acid (13.49–14.48 g/
average molecular weight of the oils but also their purity. .e
100 g), palmitic acid (5.27–5.97 g/100 g), and stearic acid
saponiﬁcation value of hot-pressed rapeseed oil extracted (4.82–5.16 g/100 g). .e total SFA contents were
using Soxhlet extraction was the lowest with a value of
10.25–10.97 g/100 g, and the total UFA content was
173.21 mg/g, and this may be due to the fact that the oil
86.57–91.05 g/100 g. .e overall fatty acid proﬁle of ﬂaxseed
contains some impurities that cannot be saponiﬁed.
oils was similar to that reported previously [35].
.e eﬀects of diﬀerent extraction methods on the
composition and content of fatty acids in ﬂaxseed oil were
3.4. Fatty Acid Proﬁle. .e fatty acid proﬁles of rapeseed and
the same as those in rapeseed oil. .e content of linolenic acid
ﬂaxseed oils extracted by diﬀerent methods are presented in
in cold-pressed ﬂaxseed oil extracted from a screw press was
Table 2. Five major fatty acids presented in the two types of
the highest, 1.10%–6.90% higher than that in other treatment
oils were palmitic acid (C16 : 0), stearic acid (C18 : 0), oleic
groups. In addition, the linoleic acid content of hot-pressed
acid (C18 : 1), linoleic acid (C18 : 2), and linolenic acid (C18 :
ﬂaxseed oil extracted by hydraulic press increased by 4.73% to
3). Oleic acid and linoleic acid (64.20–67.42 g/100 g and
11.06% compared with other treatment groups. Teixeira et al.
15.01–15.82 g/100 g, respectively) were the most abundant
[36] also used statistical analysis to show a signiﬁcant dif-
fatty acids found in the rapeseed oils, followed by linolenic
ference (P < 0.05) between fatty acid compositions in samples
acid (7.82–9.68 g/100 g), palmitic acid (3.31–4.75 g/100 g),
extracted by diﬀerent extraction methods.
and stearic acid (2.38–2.89 g/100 g). .e contents of oleic
acid, linoleic acid, and linolenic acid, which are unsaturated
fatty acids (UFA), and palmitic acid and stearic acid, which
3.5. Triglycerides. .e eﬀects of diﬀerent extraction methods
are saturated fatty acids (SFA), were determined. .e
on composition of triacylglycerols in rapeseed and ﬂaxseed
contents of saturated and unsaturated fatty acids in rapeseed
oils are shown in Table 3. Some functional properties of oils
oil were 5.69–7.64 g/100 g and 87.03–92.75 g/100 g, respec-
depend on not only their fatty acid composition but also the
tively. .e overall fatty acid proﬁle of rapeseed oils presented
distribution of the fatty acids at the three positions of the
in this work is similar to that reported previously [34]. In this
glycerol backbone. .e predominant triglycerides presented
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in rapeseed oil included OOO (37.26%–41.94%), OOL
.e major volatile compounds in ﬂaxseed oils are acids
(21.90%–23.62%), and OLL (17.03–19.16%). .e major fatty
(5.36%–32.27%), aldehydes (1.97%–34.77%), heterocycles
acids constituting triglycerides were oleic acid and linoleic
(7.26%–46.79%), alcohols (3.51%–29.53%), and ketones
acid. .is result is in accordance with the GC analysis of total
(2.18%–20.76%). Diﬀerent oil preparation processes and
fatty acid content in rapeseed oil, in which the compositions
pretreatment aﬀected the contents of volatile compounds in
of oleic acid (64.20–67.42 g/100 g) and linoleic acid
ﬂaxseed oils. Compared to other ﬁndings, Danh et al. [38]
(15.01–15.82 g/100 g) were highest (Table 2). Diﬀerent ex-
have also revealed that the volatile components of the lav-
traction methods had no signiﬁcant eﬀect (P > 0.05) on the
ender essential oils exhibit considerable variations among
compositions and contents of triglycerides. Compared with the extraction methods.
blank control, the composition and content of triglyceride in
Acids accounted for 5.36%–32.27% of total volatiles in
rapeseed oil were not signiﬁcantly aﬀected by roasted pre-
ﬂaxseed oils; however, they have a relatively high
treatment (P > 0.05).
threshold value and do not signiﬁcantly contribute to the
Eight types of triglycerides were found in ﬂaxseed oil:
odor of vegetable oils. .erefore, the aroma of oils ob-
LnLnLn, LLnLn, OLnLn, LLL, OLL, OOL, OOO, and POO.
tained by the experiment is mainly due to only several
Among all these triglycerides, OLnLn (21.37%–23.44%),
volatile components. .e content of aldehydes in ﬂaxseed
OLL (17.62%–17.82%), LnLnLn (14.74%–16.16%), and LLL
oils extraction from screw press was the highest, which
(13.20%–13.70%) constituted the main body of triglycerides,
was 1.70–17.65 and 1.70–3.50 times those of hydraulic
and the sum of their contents exceeded 71% of total content
press and Soxhlet extraction, respectively. Alcohols have
of triglycerides. .is is consistent with the results from fatty
aromatic, vegetative, rancid, and earthy ﬂavors. Alcohols
acid determination, in which the content of linolenic acid
were detected mainly in the cold-pressed ﬂaxseed oil
(Ln) was found to be highest (47.72–51.01 g/100 g). Diﬀerent
obtained from hydraulic press method, which were
extraction methods and pretreatment had no signiﬁcant
3.00–8.40 times higher than those in other treatment
eﬀect (P > 0.05) on the compositions and contents of tri-
groups. Heterocyclic substances are the products of the
glycerides, which was consistent with the results of rapeseed
Maillard reaction, which mainly include pyrazine, furan, oil.
pyrrole, pyrimidine, and thiazole. High protein oilseeds
are the basic materials for the Maillard reaction. As can be
seen from Table 4, the contents of heterocyclic substances
3.6. Volatile Compounds. .e eﬀects of diﬀerent extraction
in ﬂaxseed oil samples extracted using screw press and
processes on the volatile components of rapeseed and
hydraulic press methods were higher than those in oil
ﬂaxseed oils are presented in Table 4. A total of 8 volatile
samples extracted using Soxhlet extraction. In particular,
compounds, aldehydes, acids, alcohols, heterocycles, al-
the contents of heterocyclic substances in hot-pressed
kanes, esters, ketones, and oleﬁns, were identiﬁed in the two
ﬂaxseed oil extraction by the hydraulic press were the
types of oils. Aldehydes, acids, alcohols, heterocycles, and
highest, 2.50–6.50 times higher than those in other
ketones were the main volatile components identiﬁed in treatment groups.
rapeseed oils. .e contents of alkanes, esters, ketones, and
alkenes were lower than those of other volatile compounds.
Aldehydes mainly impart the fresh, green, grass, and fatty
3.7. Total Phenol Content and Vitamin E. Total phenol and
ﬂavors of oils, while heterocycles play a crucial role in their
vitamin E contents of rapeseed and ﬂaxseed oils extracted
nutty and roasted ﬂavors. In addition, some alcohols (fruity,
using diﬀerent methods are presented in Figure 3. .e total
coconut) and ketones (ﬂoral, fragrant) also contribute to the
phenolic contents in rapeseed and ﬂaxseed oils were
ﬂavors of oils. Aldehydes are the oxidized products of lipids,
102.66–191.67 μg/g and 120.16–147.83 μg/g, respectively.
mainly linoleic acids and linolenic acids. Aldehydes were .e contents of vitamin E in rapeseed oil
found to be the dominant volatile compounds accounting
(474.70–849.30 mg/kg) were signiﬁcantly higher than those
for 1.85%–22.62% of the total amounts of volatiles in the oil
in ﬂaxseed oil (330.30–424.90 mg/kg).
samples. Zhong et al. [37] have determined the volatile
Furthermore, the total phenol contents of the two types
components in cold-pressed camellia oil and reported the
of oils prepared by Soxhlet extraction method were the
presence of nine saturated aldehydes, from valeraldehyde to
highest. .e total phenol contents in hot-pressed oils were
nonanoic acid, in the oil. .e volatile components of
higher than those of cold-pressed oils, which was consistent
rapeseed oils were signiﬁcantly aﬀected by diﬀerent ex-
with the work of Wang et al. [39] on the steam explosion
traction methods. In addition, the contents of various vol-
pretreatment of rapeseed. In particular, the total phenol
atile components in rapeseed oil are aﬀected by roast
contents of hot-pressed rapeseed oil and ﬂaxseed oil
pretreatment. .e contents of acids, aldehydes, and alcohols
extracted by Soxhlet extraction increased by 21.88%–68.10%
in cold-pressed rapeseed oil extraction by the hydraulic press
and 1.11%–23.03%, respectively, compared to other
were the highest, which were 2.33–6.53, 1.34–3.47, and
methods. .is may be due to the fact that the extraction time
1.41–4.2 times those in other treatment groups, respectively.
of the Soxhlet extraction method was 8 h, which was 12–60
.e contents of heterocycles and ketones compounds in hot-
times longer than that of other methods. Moreover, the
pressed rapeseed oil extraction from screw press were, re-
Soxhlet extraction was continuously repeated using a con-
spectively, 1.30–3.00 and 1.34–3.37 times higher than those
densed pure solvent; as a result, the total phenol content was in other treatment groups.
the highest. .ese results indicate that diﬀerent extraction
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Table 4: SPME-GCMS analysis of volatile compounds in rapeseed and ﬂaxseed oils. Extraction Volatile compounds (%) Oil sample Pretreatment methods
Acids Aldehydes Heterocycles Alcohols Alkanes Esters Ketones Alkenes Other Hot 10.77 1.85 23.9 16.01 0.5 1.38 13.45 1.87 30.27 Screw press Cold 17.75 15.12 11.12 13.03 0.87 1.63 3.99 1.58 34.91 Hot 11.99 6.52 18.43 5.79 1.52 3.96 10.05 4.3 37.44 Rapeseed oil Hydraulic press Cold 43.22 22.62 — 18.29 3.26 — 12.6 — 0.01 Hot 18.53 13.52 12.97 4.35 7.56 0.37 7.81 18.57 16.32 Soxhlet extraction Cold 6.62 16.83 7.96 8.18 10.12 4.2 7.78 4.44 33.87 Hot 32.27 34.77 12.06 9.5 2.92 3.32 2.68 — 2.48 Screw press Cold 31.24 26.38 18.82 6.19 1.39 1.99 5.24 — 8.75 Hot 5.36 1.97 46.79 4.69 1.2 3.75 2.18 31.52 2.54 Flaxseed oil Hydraulic press Cold 25.48 15.46 10.58 29.53 — — 15.02 — 3.93 Hot 21.62 9.94 10.17 3.51 7.31 5.81 20.76 3.18 17.7 Soxhlet extraction Cold 20.72 15.65 7.26 10.12 8.8 2.05 13.55 2.32 19.53
Note. —: less than 0.5% or undetectable. 200 a 1000 180 b a b 160 800 A A c A d B 140 d c C µg/g) 120 e C g/kg) 600 ls ( d 100 e f heno A B 80 400 D C E E itamin E (m Total p 60 V 40 200 20 0 0 crew ulic ulic crew crew ulic ulic crew f s oxhlet oxhlet oxhlet oxhlet ydra f s f s f s f s ydra f s ydra f s ydra f s ed o f h ed o f h ed o f h ed o f h ed o ed o ed o ed o ress ed o ress ed o ress ed o ress ed o ress ress ress ress ot p ress ress ot p ress ress H ot p old p H ot p old p ot p H C old p ot p H C old p H C old p C old p C H C Rapeseed oil Rapeseed oil Flaxseed oil Flaxseed oil (a) (b)
Figure 3: Total phenol and vitamin E contents in rapeseed and ﬂaxseed oils. (a) Total phenol. (b) Vitamin E.
processes signiﬁcantly aﬀected the total phenol contents in
other methods. Compared with screw press, the vitamin E the two types of oils.
loss rates of the two oils obtained by hydraulic press and
.e vitamin E contents in the two types of oils were also
Soxhlet extraction were 14.00%–41.00% and 4.00%–44.00%,
signiﬁcantly diﬀerent and were aﬀected by other extraction
respectively. In general, the vitamin E content of the oil can
processes. .e vitamin E content of rapeseed oil is ∼2 times be increased by screw press.
that of ﬂaxseed oil. .e vitamin E content of rapeseed oil and
ﬂaxseed oil produced by screw press was higher than that of 4. Conclusion
the hydraulic press and Soxhlet extraction. In addition,
the contents of vitamin E in cold-pressed rapeseed oil
.e mechanical press was considered superior to the Soxhlet
and ﬂaxseed oil obtained by screw press increased by
extraction method in terms of sensory score and physico-
1.22%–78.91% and 3.00%–18.80%, respectively, compared to
chemical indexes (acid value, peroxide value, saponiﬁcation
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value, moisture, and volatiles). .e physicochemical indexes
Research Transformation and Industrialization Special
of oil extracted by the screw press method were comparable
Project (Grant no. 2021-NK-C19).
to those of oil extracted by the hydraulic press. .e contents
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