Outline: Milk Spoilage in Food Microbiology | Môn Microbiology - Trường Đại học Quốc tế, Đại học Quốc gia Thành phố Hồ Chí Minh

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Outline: Milk Spoilage in Food Microbiology for Food Technology
1. Introduction – The Role of Milk Spoilage in Food Technology
● Definition of Milk Spoilage in Food Microbiology:
○ Sự biến đổi không mong muốn của sữa do tác động của vi sinh vật, enzyme,
và các phản ứng hóa học, ảnh hưởng trực tiếp đến chất lượng sản phẩm trong
chuỗi sản xuất thực phẩm.
● Relevance to Food Technology:
○ Ứng dụng các phương pháp kiểm soát vi sinh vật và công nghệ bảo quản để
kéo dài hạn sử dụng và giảm thiểu tổn thất.
● Importance of Controlling Milk Spoilage:
○ Economic Impact: Giảm tổn thất trong sản xuất và phân phối.
○ Food Safety: Ngăn ngừa nguy cơ lây nhiễm vi khuẩn gây bệnh.
○ Sustainability: Tối ưu hóa tài nguyên và giảm thiểu lãng phí thực phẩm.
2. Factors Affecting Milk Spoilage in Food Technology
● 1. Biological Factors:
○ Vai trò của vi sinh vật trong hư hỏng sữa và ứng dụng các phương pháp kiểm
soát như tiệt trùng và vi lọc (microfiltration).
● 2. Environmental Factors:
○ Tầm quan trọng của kiểm soát nhiệt độ trong chuỗi lạnh (cold chain) và giảm
thiểu tác động của ánh sáng trong bảo quản.
● 3. Handling and Processing Factors:
○ Ứng dụng thực hành sản xuất tốt (GMP) và phân tích mối nguy và kiểm soát
điểm tới hạn (HACCP) trong quy trình sản xuất sữa.
3. Spoilage Process and Mechanisms – From Microbiology to Technology
● 1. Microbial Growth and Metabolism:
○ Phân tích sự phát triển của vi sinh vật ở các giai đoạn sản xuất và bảo quản sữa.
○ Sử dụng công nghệ như PCR hoặc giải trình tự gen để nhận diện vi sinh vật gây hư hỏng.
● 2. Enzymatic Activity:
○ Ứng dụng enzyme học trong việc phát triển các chỉ thị sinh học (biosensors)
để phát hiện sớm hư hỏng sữa.
● 3. Chemical Changes and End Products:
○ Kiểm soát sự hình thành sản phẩm phụ của vi sinh vật thông qua công nghệ đóng gói tiên tiến.
4. Prevention and Sustainability – Technological Solutions
● 1. Hygiene Control and Good Manufacturing Practices (GMP): lOMoAR cPSD| 58504431
○ Ứng dụng các hệ thống giám sát tự động và robot hóa trong khâu vệ sinh dây chuyền sản xuất.
● 2. Preservation Techniques:
○ Công nghệ tiệt trùng nhiệt độ cao trong thời gian ngắn (HTST) và tiệt trùng
nhiệt độ cực cao (UHT) trong tối ưu hóa bảo quản sữa.
○ Sử dụng màng lọc sinh học và công nghệ bao bì thông minh (smart packaging)
để kéo dài hạn sử dụng.
● 3. Sustainability Practices:
○ Áp dụng công nghệ Internet of Things (IoT) trong giám sát chuỗi lạnh.
○ Tối ưu hóa quy trình sản xuất theo mô hình kinh tế tuần hoàn (circular
economy) để giảm thiểu lãng phí.
5. Conclusion – Integrating Food Microbiology in Food Technology
● Tầm quan trọng của việc ứng dụng vi sinh vật học thực phẩm trong kiểm soát chất
lượng và phát triển các công nghệ bảo quản hiện đại.
● Hướng đi tương lai: Sử dụng công nghệ sinh học và AI để tối ưu hóa quy trình kiểm soát hư hỏng sữa. lOMoAR cPSD| 58504431
1. Introduction – The Role of Milk Spoilage in Food Technology
🥛 1.1. Definition of Milk Spoilage in Food Microbiology
Milk spoilage refers to undesirable changes in milk caused by microbial activity, enzymatic
reactions, and chemical transformations. In food microbiology, milk serves as a perfect growth
medium for microorganisms due to its rich nutrient profile, including lactose, proteins, fats,
vitamins, and minerals. When microbial contamination occurs, these microorganisms
metabolize milk components, leading to off-flavors, souring, curdling, gas formation, and other quality degradations.
● Key Microorganisms Involved:
○ Pseudomonas spp. – Psychrotrophic bacteria capable of growing at
refrigeration temperatures, producing heat-stable proteases and lipases.
○ Lactobacil us spp. and Streptococcus spp. – Lactic acid bacteria responsible
for lactose fermentation, resulting in acidification and coagulation.
○ Bacil us spp. – Spore-forming bacteria that survive pasteurization, contributing to late-stage spoilage. Reference:
● Ternström, A., Lindberg, A. M., & Molin, G. (1993). Classification of the spoilage flora
of raw and pasteurized bovine milk, with special reference to Pseudomonas and
Bacil us. International Journal of Food Microbiology, 17(2), 83–102.
● Quigley, L., O'Sullivan, O., Beresford, T. P., Ross, R. P., Fitzgerald, G. F., & Cotter, P.
D. (2013). The complex microbiota of raw milk. FEMS Microbiology Reviews, 37(5), 664–698.
🌍 1.2. Importance of Controlling Milk Spoilage in Food Technology
Controlling milk spoilage is crucial not only for ensuring product safety but also for enhancing
shelf life, reducing economic losses, and minimizing environmental impacts. Let’s break down
its significance in three key areas: ● Economic Impact:
○ Spoiled milk leads to substantial financial losses at various stages of the supply
chain — from farmers to retailers.
○ The implementation of technologies like pasteurization, cold chain
management, and aseptic packaging helps reduce spoilage, optimizing
production efficiency and minimizing costs. ● Food Safety:
○ Milk can harbor pathogenic microorganisms like Salmonella, Listeria
monocytogenes, and Escherichia coli.
○ Poor handling or inadequate processing may lead to the proliferation of these
pathogens, causing severe foodborne il nesses.
○ Applying Hazard Analysis and Critical Control Points (HACCP) and Good
Manufacturing Practices (GMP) helps mitigate these risks. ● Sustainability:
○ Reducing spoilage minimizes food waste, aligning with Sustainable
Development Goals (SDGs) focused on food security and resource optimization. lOMoAR cPSD| 58504431
○ Technological innovations such as rapid microbial detection systems, smart
packaging, and blockchain traceability enhance sustainability efforts. Reference:
● McAuley, C. M., Singh, T. K., Jayarao, B. M., & Griffiths, M. W. (2012). Microbial quality
of raw milk and the influence of hygienic milk production practices. Food Control, 27(1), 201–209.
● FAO (2021). Reducing food loss and waste in the dairy sector. Food and Agriculture
Organization of the United Nations.
🌟 2. Factors Affecting Milk Spoilage in Food Technology
Milk spoilage in food technology is governed by various factors, ranging from environmental
conditions to processing and storage practices. These factors can be grouped into three main
categories: biological, environmental, and handling factors. Controlling these factors is
fundamental to minimizing spoilage and optimizing milk quality.
🧬 2.1. Biological Factors:
Microorganisms are the primary cause of milk spoilage, each group contributing to distinct spoilage mechanisms:
● Microbial Contamination:
○ Milk is a nutrient-rich medium, making it highly susceptible to microbial
contamination from sources such as cow udders, milking equipment, handlers' hands, air, and water.
○ Contamination can occur throughout the production chain: from milking and
transportation to processing and storage.
● Key Microorganisms:
○ Psychrotrophic Bacteria:
■ Thrive at cold temperatures (4–7°C), such as Pseudomonas spp.
■ Produce heat-stable enzymes like proteases and lipases, degrading
proteins and fats even after pasteurization.
○ Lactic Acid Bacteria (LAB):
■ Lactobacil us spp. and Streptococcus spp. ferment lactose into lactic
acid, lowering pH, leading to curdling and souring.
○ Spore-Forming Bacteria:
■ Bacil us spp. and Clostridium spp. form spores that can survive
pasteurization, contributing to late-stage spoilage like gas formation and sweet curdling. Reference:
● Quigley, L., O'Sullivan, O., Beresford, T. P., Ross, R. P., Fitzgerald, G. F., & Cotter, P.
D. (2013). The complex microbiota of raw milk. FEMS Microbiology Reviews, 37(5), 664–698.
🌡️ 2.2. Environmental Factors:
Environmental conditions significantly influence microbial growth and the rate of milk spoilage: ● Temperature: lOMoAR cPSD| 58504431
○ The most critical factor affecting spoilage rate.
○ High storage temperatures (>10°C) accelerate microbial growth.
○ Low temperatures (4°C) slow most microbial activity, except for psychrotrophic
bacteria like Pseudomonas spp.
● Humidity and Air Quality:
○ High humidity promotes mold growth on dairy products.
○ Poor air quality can introduce airborne contaminants, increasing microbial load. ● Light Exposure:
○ Light, especially UV rays, triggers oxidative reactions, leading to rancidity and off-flavors.
○ UV light also degrades riboflavin (Vitamin B2), reducing milk's nutritional value. Reference:
● Cousin, M. A., Jay, J. M., & Vasavada, P. C. (2001). Psychrotrophic microorganisms.
Compendium of the Microbiological Spoilage of Foods and Beverages (pp. 41–67). Springer.
🗳️ 2.3. Handling and Processing Factors:
Handling and processing practices in food technology play a crucial role in determining milk's shelf life and quality: ● Milking Hygiene:
○ Inadequate hygiene during milking can introduce environmental bacteria from
cow udders, equipment, or handlers.
○ Sanitizing milking equipment and monitoring animal health is essential.
● Pasteurization and Heat Treatment:
○ High-Temperature Short Time (HTST): 72°C for 15 seconds.
○ Ultra-High Temperature (UHT): 135–150°C for 2–5 seconds, ensuring
extended shelf life without refrigeration.
○ However, certain bacterial spores, like Bacil us cereus, can survive
pasteurization, leading to delayed spoilage.
● Cold Chain Management:
○ Maintaining continuous refrigeration from milking to consumption is critical to preventing microbial growth.
○ Any break in the cold chain can create favorable conditions for bacterial proliferation.
● Packaging and Transportation:
○ Poor packaging or leakage can cause secondary contamination postpasteurization.
○ Using UV-blocking and oxygen-barrier packaging protects milk from external spoilage factors. Reference:
● Walstra, P., Wouters, J. T. M., & Geurts, T. J. (2005). Dairy Science and Technology,
Second Edition. CRC Press.
Dưới đây là một số ý tưởng cho biểu đồ và hình ảnh minh họa trong phần phân tích
"Factors Affecting Milk Spoilage":
1. Biểu đồ phân loại vi sinh vật:
○ Trục X: Nhiệt độ phát triển tối ưu. lOMoAR cPSD| 58504431
○ Trục Y: Tốc độ sinh trưởng.
○ Nhóm vi khuẩn: Psychrotrophic, Mesophilic, Thermoduric.
2. Sơ đồ các yếu tố môi trường ảnh hưởng đến sữa:
○ Hình tròn trung tâm là "Milk Spoilage."
○ Các nhánh tỏa ra là: Nhiệt độ, Độ ẩm, Ánh sáng, Chất lượng không khí.
3. Biểu đồ quy trình xử lý và bảo quản:
○ Quy trình: Vắt sữa → Làm lạnh nhanh → Vận chuyển → Tiệt trùng → Đóng gói → Phân phối.
○ Mỗi bước có ghi chú về nguy cơ nhiễm khuẩn và biện pháp kiểm soát. 3.
Spoilage Process and Mechanisms – From Microbiology to Technology
Milk spoilage is a complex process involving microbial activity, enzymatic reactions, and
chemical changes. Understanding these mechanisms is crucial for developing effective control
strategies in food technology. Let’s break it down into three stages:
3.1. Microbial Growth and Metabolism:
Microbial activity is the primary driver of milk spoilage. Key microbial groups include:
● Psychrotrophic Bacteria: Thrive at refrigeration temperatures (4–7°C) and dominate
spoilage in refrigerated milk. Pseudomonas spp. is a major psychrotroph, producing
heat-stable proteases and lipases capable of degrading proteins and fats, even after pasteurization.
● Mesophilic Bacteria: Grow optimally at 20–40°C and become dominant when milk is
stored at room temperature. Lactobacil us spp. and Streptococcus spp. are
responsible for lactic acid production and souring.
● Thermoduric Bacteria and Spores: Survive pasteurization and proliferate during
storage, contributing to late-stage spoilage. Bacil us cereus spores can germinate
post-pasteurization, leading to sweet curdling and gas formation.
Reference: Ternström, A., Lindberg, A. M., & Molin, G. (1993). Classification of the spoilage
flora of raw and pasteurized bovine milk, with special reference to Pseudomonas and Bacil us.
International Journal of Food Microbiology, 17(2), 83–102.
⚙️3.2. Enzymatic Activity:
Microbial enzymes play a key role in breaking down milk’s main components — lactose,
proteins, and fats — causing undesirable changes:
● Proteolysis: Bacterial proteases hydrolyze casein and whey proteins, resulting in
bitterness, sliminess, and curdling. Pseudomonas fluorescens produces heat-stable
proteases that remain active even after pasteurization.
● Lipolysis: Lipases hydrolyze milk fat into free fatty acids, leading to rancidity and
offflavors. Psychrotrophic bacteria like Pseudomonas spp. are major producers of lipases.
● Lactose Fermentation: Lactic acid bacteria (LAB) convert lactose into lactic acid,
lowering pH and causing souring. Lactobacil us spp. and Streptococcus spp. are
primary fermenters, producing acidification and coagulation. lOMoAR cPSD| 58504431
Reference: Chen, L., Daniel, R. M., & Coolbear, T. (2003). Detection and impact of protease
and lipase activities in milk and milk powders. International Dairy Journal, 13(4), 255–275.
🧪 3.3. Chemical Changes and End Products:
The metabolic activity of microbes results in various chemical changes that degrade milk quality:
● Acidification: As lactose is fermented into lactic acid, pH drops, leading to curdling and sour flavor.
● Gas Production: Certain bacteria (Coliforms, Clostridium spp.) produce gases like
CO and H , causing bloating in milk containers.₂ ₂
● Off-flavor and Odor Formation: Degradation of proteins and fats generates sulfur
compounds, amines, and short-chain fatty acids, contributing to unpleasant smells and flavors.
● Color Changes: Microbial activity can produce pigments, resulting in abnormal
discoloration (e.g., blue milk due to Pseudomonas spp.).
Reference: Griffiths, M. W., & Phil ips, J. D. (1990). Incidence, source, and some properties of
psychrotrophic Bacil us species in raw and pasteurized milk. Journal of Dairy Research, 57(3), 465–471.
By understanding these processes, food technologists can develop targeted interventions to
reduce spoilage, enhance shelf life, and improve milk safety.
4. Prevention and Sustainability
4.1. Hygiene Control and Good Manufacturing Practices (GMP):
Maintaining strict hygiene throughout the milk production chain is crucial to preventing
contamination and extending shelf life. Key measures include: Milking Hygiene:
● Pre- and Post-Milking Cleaning: Cleaning the cow's udder with a disinfectant solution
before milking minimizes the entry of environmental bacteria like Escherichia coli or Staphylococcus aureus.
● Animal Health Monitoring: Regular health checks of the herd, especially for mastitis,
reduce the risk of bacterial transmission into milk. Plant Sanitation:
● Cleaning and Disinfecting Equipment: Pipelines, storage tanks, and processing
machinery should undergo regular cleaning with Cleaning-In-Place (CIP) systems and
disinfection to prevent biofilm formation, especially from spore-forming bacteria like Bacil us cereus.
● Hazard Analysis and Critical Control Points (HACCP): Implementing HACCP helps
identify potential risks in the production process and establishes measures to mitigate them. Cold Chain Management: lOMoAR cPSD| 58504431
● Temperature Control: Milk must be rapidly cooled to 4°C immediately after milking to
limit the growth of psychrotrophic bacteria such as Pseudomonas spp..
● Storage and Transport: Maintaining a continuous cold chain from production to
consumer extends shelf life and prevents rapid bacterial proliferation. Reference:
● McAuley, C. M., Singh, T. K., Jayarao, B. M., & Griffiths, M. W. (2012). Microbial quality
of raw milk and the influence of hygienic milk production practices. Food Control, 27(1), 201–209.
4.2. Preservation Techniques:
Preservation techniques aim to minimize microbial growth and extend milk’s shelf life. Pasteurization:
● HTST Pasteurization: Heating milk at 72°C for 15 seconds eliminates most spoilage
microorganisms while preserving nutritional value.
● UHT Sterilization: Treating milk at 135–150°C for 2–5 seconds eliminates all
microorganisms, allowing long-term storage without refrigeration.
Filtration and Microfiltration:
● Bacterial Removal: Filtering milk through microfilters reduces bacterial load and
spores before pasteurization, enhancing preservation.
● Membrane Technology: Often combined with pasteurization or sterilization, this
technology minimizes heat impact, preserving milk’s natural flavor. Packaging Innovations:
● UV-Blocking Packaging: Using plastic bottles or aluminum-coated cartons that block
UV light prevents oxidation, maintaining milk’s color and flavor.
● Smart Packaging Technology: Some modern packaging incorporates sensors that
monitor temperature or pH, providing real-time quality tracking.
Natural Antimicrobials and Biopreservation:
● Bacteriocins Use: Nisin, a natural antimicrobial peptide produced by Lactococcus
lactis, is added as a biopreservative to inhibit spoilage bacteria.
● Plant Essential Oils: Essential oils from basil, lemongrass, or peppermint exhibit
strong antibacterial properties, reducing bacterial growth in milk. Reference:
● Chen, L., Daniel, R. M., & Coolbear, T. (2003). Detection and impact of protease and
lipase activities in milk and milk powders. International Dairy Journal, 13(4), 255–275.
4.3. Sustainability Practices:
Sustainable practices reduce food waste and minimize the environmental impact of the dairy industry.
Reducing Waste Along the Supply Chain: lOMoAR cPSD| 58504431
● Optimizing Transport: Reducing the time between milking and consumption
minimizes spoilage and optimizes supply chain efficiency.
● IoT Integration: Sensors monitor temperature and humidity during transport, ensuring
optimal conditions throughout the cold chain. Reusing and Recycling:
● By-Product Utilization: Dairy by-products like whey can be used as animal feed or
processed into value-added products like yogurt or cheese.
● Biological Treatment: Spoiled milk can undergo anaerobic fermentation to produce
biogas, contributing to renewable energy development. Consumer Awareness:
● Raising Awareness: Educating consumers on proper milk storage and the difference
between “use-by” and “best-before” labels reduces food waste.
● Waste Reduction Initiatives: Many dairy companies are promoting sustainability
campaigns, encouraging responsible consumption and supporting circular economy practices. Reference:
● FAO (2021). Reducing food loss and waste in the dairy sector. Food and Agriculture
Organization of the United Nations.