lOMoAR cPSD| 45764710
Answers for the oral test Question 1
1. What is cleaning? Give examples.
- Cleaning is the unit operation in which contaminating materials are removed from
foods and separated to leave the surface of the food in a suitable condition for further processing.
- Examples: Peeling fruits and vegetables, skinning meat or descaling fish, blanching
2. Name the kinds of cleaning and their main equipments?
- Cleaning is categorized into wet procedures, and dry procedures
- The main groups of equipment used for wet cleaning are: spray washers, brush
washer, drum or piston washers and flotation tanks. And for dry cleaning are: air
classifiers, magnetic separators and separators based on screening foods. Question 2:
1. What is wet cleaning used for?
Wet cleaning is used for removing soil from root crops or dust and pesticide residues from soft fruits or vegetables.
2. What are the advantages of wet cleaning?
+ Wet cleaning is more effective than dry methods for removing soil from root crops
or dust and pesticide residues from soft fruits or vegetables.
+ It is also dustless and causes less damage to foods than dry methods.
+ Different combinations of detergents and sterilants at different temperatures allow flexibility in operation Question 3:
1. What is wet cleaning used for?
Wet cleaning is used for removing soil from root crops or dust and pesticide residues from soft fruits or vegetables.
2. What are the disadvantages of wet cleaning?
+ the use of warm cleaning water may accelerate chemical and microbial spoilage
+ wet procedures produce large volumes of effluent, often with concentrations of
dissolved (đi do vựt) and suspended solids
+ There is then a requirement/ both to purchase clean water/ and to pay for high effluent disposal charges Question 4:
1. What are dry cleaning procedures used for? lOMoAR cPSD| 45764710
Dry cleaning procedures are used for products that are smaller/, have greater mechanical
strength/ and possess a lower moisture content (for example grain and nuts).
2. The advantages of dry cleaning?
+ After cleaning, the surfaces are dry, to aid preservation for further (phơ dờ) drying.
+ Dry procedures generally involve smaller cheaper equipment than wet procedures do
+ and produce a concentrated dry effluent which may be disposed (đít’s pâu’s) of more cheaply.
+ Plant cleaning is simpler/ and chemical and microbial deterioration of the food is reduced. Question 5:
1. What is dry cleaning procedures used for?
Dry cleaning procedures are used for products that are smaller, have greater mechanical
strength and possess a lower moisture content (for example grain and nuts).
2. The disadvantages of dry cleaning?
+ Additional capital expenditure may be necessary to prevent the creation of dust that not
only creates a health hazard but also recontaminates the product Question 6:
1. What are the extracted components(oil and juices) used for?
Components are extracted from plant materials either for direct consumption (for example,
fruit juices) or for use in subsequent processing (for example sugar and vegetable oils).
2. In fruit processing, how is the press achieved?
In fruit processing, the press is achieved by the use of lower pressure and fewer pressings.
It is also necessary to increase the pressure slowly to avoid the formation of a dense
impenetrable press cake, as the solid material is easily deformed. Question 7:
1. Two methods of oil extraction?
There are two methods of oil extraction: solvent extraction and expression.
2. What factors influence the yield liquid from a press?
The factors that influence the yield liquid from a press include: the maturity and growth
conditions of the raw material, the extent of disruption of cell structure, the resistance of lOMoAR cPSD| 45764710
the solids to mechanical deformation, the rate of increase in pressure, the time of pressing
and the thickness of the pressed solids. Question 8:
1.What is size reduction in food processing?
Size reduction is the unit operation in which the average size of solid pieces of food is
reduced by the application of grinding, compression or impact forces.
2.What are the main benefits of size reducion?
(1) There is an increase in the surface-area-to-volume ratio of the food which increases
the rate of drying, heating or cooling and improves the efficiency and rate of
extraction of soluble components.
(2) When combined with screening, a pre-determined range of particle size is produced.
(3) A similar range of particle sizes allows more complete mixing of ingredients Question 9:
1. Definition of chilling?
Chilling is the unit operation in which the temperature of a food is reduced to between – 1ºC and 8ºC.
2. The advantages of chilling? -
Chilling retards microbial spoilage, to prevent the growth of pathogens, and to
extend the shelf life of fresh and processed foods. -
Chilling causes minimal changes to flavours and nutritional properties of foods, and
as aresult, chilled foods are perceived by consumers as being “ healthy” and “ fresh”. Question 10:
1.Why is heat treatment one of the most methods used in food processing?
Because of the desirable effects on eating quality (many foods are comsumed in cooked
form) and the preservative effect on foods by the destruction of enzyme and microbial
activity, insects and parasites.
2. What are the other main advantages of heat processing?
The main advantages of heat processing are lOMoAR cPSD| 45764710
- destruction of anti-nutritional components of foods,
- improvement in availability of some nutrients and
- relatively simple control of processing conditions.