Microbial Spoilage of Milk and Milk Products – Cream, Butter, Cheese, Yoghurt, Ice-cream

What is Microbial Spoilage of Milk and Milk Products?

• Microbial spoilage of milk and milk products refers to the deterioration in quality and safety caused by the growth of microorganisms such as bacteria, yeasts, and molds. These microorganisms can contaminate milk and milk products during production, processing, handling, and storage, leading to changes in sensory characteristics, reduced shelf life, and potential health risks.
• Bacteria are the primary cause of microbial spoilage in milk and milk products. They can multiply rapidly under favorable conditions, utilizing nutrients in the milk and producing byproducts that result in undesirable changes. Common spoilage bacteria include psychrotrophic bacteria (able to grow at low temperatures), mesophilic bacteria (able to grow at moderate temperatures), and thermophilic bacteria (able to grow at high temperatures).
• Yeasts and molds can also contribute to milk spoilage, although they are less common compared to bacteria. Yeasts are capable of fermenting lactose, leading to the production of off-flavors and gas, while molds can grow on the surface of milk products and produce visible colonies, causing discoloration and texture changes.
• Microbial spoilage of milk and milk products can result in various signs of spoilage, including off-flavors, off-odors, changes in texture, curdling, gas production, separation of whey, sliminess, and visible mold growth. These changes make the products unappealing, reduce their market value, and can pose a risk to consumer health if pathogenic microorganisms are present.
• Preventing microbial spoilage of milk and milk products involves proper hygiene and sanitation practices throughout the production and processing chain, including maintaining clean milking equipment, cooling milk rapidly after milking, pasteurization or heat treatment to destroy spoilage and pathogenic microorganisms, and maintaining proper storage conditions, such as refrigeration. Packaging materials and techniques also play a role in preventing contamination and extending shelf life.
• Regular monitoring and testing for microbial quality, including total bacterial counts and the presence of specific spoilage organisms, are important to ensure the safety and quality of milk and milk products. Prompt detection and appropriate corrective actions can help prevent the spread of spoilage microorganisms and minimize product losses.

Contamination Source for Spoilage of Milk and Milk Products

Contamination sources for the spoilage of milk and milk products can originate from various points within the production and processing chain. Here are some key sources of contamination:

1. Milking animals: The milk obtained from animals such as cows, buffalo, sheep, and goats can be a source of contamination. The exterior of the udder, including the teats and surrounding skin, may harbor bacteria and other microorganisms that can contaminate the milk during the milking process.
2. Milking equipment: The equipment used for milking, such as milking machines, pipelines, and storage tanks, can harbor bacteria and biofilms. If not properly cleaned and sanitized, these surfaces can introduce contaminants into the milk.
3. Environment: The surrounding air and environment of the farm or dairy facility can contribute to milk contamination. Airborne microorganisms, dust particles, and insects can contaminate the milk during milking and subsequent handling.
4. Animal feed: The quality and safety of the animal feed can impact the quality of milk. Contaminated or spoiled feed can introduce harmful microorganisms or toxins into the animal’s system, which can then be passed into the milk.
5. Water quality: Water used for cleaning milking equipment, udder washing, and other dairy processes must be of high quality. Contaminated water can introduce bacteria, fungi, or other harmful microorganisms into the milk.
6. Handling and storage equipment: The quality and cleanliness of the equipment used for handling, transporting, and storing milk are critical. Contaminated equipment can introduce spoilage bacteria or other microorganisms into the milk, leading to accelerated spoilage.
7. Biofilms: Biofilms are slimy microbial communities that can form on surfaces such as pipes, tanks, and equipment in dairy processing plants. These biofilms can harbor bacteria and other microorganisms, providing a continuous source of contamination if not effectively managed.

Spoilage of milk

Spoilage of milk refers to the deterioration of milk quality caused by microbial growth and metabolic activities. Here are some key points regarding milk spoilage:

• Milk provides an ideal environment for microbial growth due to its high water content, moderate pH, and rich nutrient composition.
• Raw milk and pasteurized milk can contain various microorganisms, and even refrigeration does not prevent spoilage completely.
• Psychrotrophic microorganisms can grow in refrigerated milk storage before pasteurization, including species like Pseudomonas, Flavobacterium, Alcaligenes, Listeria monocytogenes, Yersinia enterocolitica, coliforms, and certain Bacillus spp.
• Some microorganisms, known as thermoduric microorganisms, can survive pasteurization and cause milk spoilage. These include species like Micrococcus, Enterococcus, Streptococcus, certain Lactobacillus spp., and spores of Bacillus and Clostridium.
• Molds and yeasts are usually eliminated during pasteurization but can cause spoilage in milk after heat treatment. Examples include Aspergillus, Byssochlamys, Cladosporium, and Candida spp.
• Protozoan pathogens like Cryptosporidium and Giardia have been found to contaminate milk, although their occurrence is relatively rare.
• Milk spoilage can lead to various defects, including off-flavors, discoloration, gas production, souring (lactic acid production), proteolysis, lipolysis (rancidity), sweet curdling, and gelation.
• Different microorganisms are associated with specific defects, such as Bacillus spp. causing shorter shelf life, rancidity, and bitterness; psychrotrophic bacteria causing gelation; Pseudomonas spp., Flavobacterium, Acinetobacter, and Alcaligens causing undesirable flavors; lactic acid bacteria causing sourness; coliforms, Pseudomonas spp., Alcaligenes, Micrococcus, and Bacillus subtilis causing ropiness or sliminess.
• Various flavors, including sour or acid flavors, burnt or caramel flavors, and off-color changes like blue, yellow, red, or brown milk, can also be indicators of milk spoilage caused by specific microorganisms.

Overall, milk spoilage is a result of the metabolic activities of different microorganisms, and proper handling, storage, and pasteurization techniques are crucial to minimize spoilage and maintain milk quality.

Spoilage of Milk products

Spoilage of milk products refers to the deterioration in quality and safety of various dairy products caused by microbial growth and activity. Here are some important points about the spoilage of milk products:

• The microbial quality of milk products is influenced by factors such as the type of milk used (raw milk, condensed milk, dried milk, etc.) and the specific product being produced (cream, butter, cheese, yogurt, etc.).
• Additionally, the inclusion of other ingredients like gelatin, nuts, fruits, sugar, chocolate, and coloring agents in milk products can also affect their microbial stability and potential for spoilage.
• The sanitary conditions of equipment and production facilities, the efficiency of pasteurization processes, and the overall hygiene practices during production, processing, and packaging play a critical role in preventing microbial contamination and spoilage.
• Improper handling, storage, and distribution can introduce spoilage microorganisms into milk products, leading to changes in taste, texture, appearance, and safety.
• The growth of bacteria, yeasts, and molds can cause various forms of spoilage in milk products, including off-flavors, gas production, texture changes, discoloration, and physical defects such as slime or curdling.
• Lactic acid bacteria are often responsible for spoilage in fermented milk products, leading to souring, increased acidity, and changes in texture.
• Yeasts and molds can grow on the surface of dairy products, resulting in mold growth, visible colonies, and off-flavors.
• The presence of pathogenic bacteria in milk products, such as Staphylococcus aureus or Salmonella, can pose a serious health risk if proper hygiene and sanitation measures are not followed.
• Adequate pasteurization and proper packaging, including the use of airtight containers and refrigeration, are essential to minimize microbial growth and extend the shelf life of milk products.
• Regular monitoring of microbial quality and adherence to good manufacturing practices (GMP) and Hazard Analysis and Critical Control Points (HACCP) protocols are important for ensuring the safety and quality of milk products.

In summary, the spoilage of milk products is influenced by various factors, including the type of product, ingredients used, production practices, and storage conditions. Proper sanitation, hygiene, and quality control measures are crucial in preventing spoilage and maintaining the safety and sensory attributes of milk products.

1. Spoilage of Cream

Spoilage of cream refers to the deterioration in quality and safety of cream due to the growth and activity of microorganisms. Here are some important points about the spoilage of cream:

• Cream is a dairy product that consists of the butterfat layer that separates from milk before homogenization. It is susceptible to microbial spoilage due to its high fat content and favorable nutrient composition.
• Psychrotrophic bacteria, which are capable of growing at refrigeration temperatures, are the main culprits for spoilage of cream. Examples of psychrotrophic bacteria that can cause spoilage include Pseudomonas, Alcaligenes, Acinetobacter, Aeromonas, and Achromobacter.
• At room temperature, other bacteria such as Corynebacterium, Bacillus, Micrococcus, Lactobacillus, and Staphylococcus can contribute to spoilage of cream.
• Cream is also susceptible to contamination by pathogenic microorganisms such as E. coli, Salmonella Typhimurium, and Listeria monocytogenes, which can pose a health risk if consumed.
• Common defects associated with spoiled cream include bitty texture, sweet curdling, bitterness, thinning in sterilized cream, yeast or fruity flavors, gas formation, and surface taints.
• Bacterial contamination can lead to off-flavors, off-odors, texture changes, and visual defects in cream, making it unappetizing and unsuitable for consumption.
• To prevent spoilage, it is important to ensure proper hygiene and sanitation during milk handling, cream production, and storage. Adequate pasteurization and cooling processes should be implemented to reduce microbial populations.
• Proper packaging, such as using airtight containers, and refrigeration are crucial for maintaining the quality and extending the shelf life of cream.
• Regular monitoring of microbial quality, adherence to good manufacturing practices (GMP), and implementation of Hazard Analysis and Critical Control Points (HACCP) protocols are essential for preventing spoilage and ensuring the safety of cream.

In summary, the spoilage of cream is primarily caused by psychrotrophic bacteria at refrigeration temperatures and other bacteria at room temperature. Contamination by pathogenic microorganisms can also occur, posing a health risk. Maintaining proper hygiene, implementing effective pasteurization and cooling processes, and practicing appropriate storage and packaging methods are crucial for preventing spoilage and ensuring the quality and safety of cream.

2. Spoilage of Butter

Spoilage of butter refers to the deterioration in quality and safety of butter due to the growth and activity of microorganisms. Here are some important points about the spoilage of butter:

• Butter is a dairy product made by separating milk and churning the cream. It is susceptible to microbial spoilage due to its high fat content and nutrient composition.
• The main source of microorganisms in butter is the cream, which is the starting material for butter production. Therefore, the primary spoilage organisms in butter are often similar to those found in cream, such as Pseudomonas, Alcaligenes, Acinetobacter, Aeromonas, and Achromobacter.
• Molds, including Thamnidium, Cladosporium, and Aspergillus, can also cause spoilage of butter, leading to surface discoloration and taints.
• In addition to spoilage microorganisms, pathogenic bacteria such as Listeria monocytogenes, Brucella, Mycobacterium, Campylobacter jejuni, Yersinia enterocolitica, and Salmonella Typhimurium can pose a health risk if present in butter.
• Common defects associated with spoiled butter include surface discoloration and taints, black discoloration, off-flavor, lipolytic spoilage, and yeasty smell.
• Bacterial spoilage can result in off-flavors, off-odors, and visual defects in butter, making it unappetizing and unsuitable for consumption.
• To prevent spoilage, it is important to ensure proper hygiene and sanitation during cream handling, butter production, and packaging. Adequate pasteurization and cooling processes should be implemented to reduce microbial populations.
• Proper packaging, such as using airtight containers, and storage at appropriate temperatures are crucial for maintaining the quality and extending the shelf life of butter.
• Regular monitoring of microbial quality, adherence to good manufacturing practices (GMP), and implementation of Hazard Analysis and Critical Control Points (HACCP) protocols are essential for preventing spoilage and ensuring the safety of butter.

In summary, the spoilage of butter is primarily caused by microorganisms present in the cream used for its production. Bacterial spoilage and mold growth can lead to surface discoloration, off-flavors, and other defects in butter. Contamination by pathogenic bacteria can also pose a health risk. Maintaining proper hygiene, implementing effective pasteurization and cooling processes, and practicing appropriate storage and packaging methods are crucial for preventing spoilage and ensuring the quality and safety of butter.

3. Spoilage of Cheese

Spoilage of cheese refers to the deterioration in quality, flavor, and texture of cheese due to the growth and activity of microorganisms. Here are some important points about the spoilage of cheese:

• Cheese is a fermented milk product made by coagulating milk with rennet, followed by the ripening process, during which various microorganisms contribute to the development of flavor and texture.
• The ripening process involves the proteolytic and lipolytic activities of different microorganisms, leading to the breakdown of proteins and fats in the cheese.
• Hard and semi-hard ripened cheeses with low moisture content are more susceptible to fungi, such as molds, compared to bacteria. Soft and fresh cheeses with higher pH, moisture content, and lower salinity are more prone to spoilage.
• Bacterial spoilage of cheese can be caused by organisms such as Clostridium spp. (including C. pasteurianum, C. butyricum, C. sporogenes, and C. tyrobutyricum), Bacillus polymyxa, Flavobacterium, Pseudomonas spp., Alcaligenes, and Achromobacter.
• Yeasts, including Candida spp., Debaryomyces hansenii, Geotrichum candidum, and Pichia spp., can also contribute to cheese spoilage.
• Mold spoilage in cheese is mainly caused by Penicillium spp. and Cladosporium spp.
• Some pathogenic bacteria, such as Listeria monocytogenes, Salmonella spp., and Escherichia coli, can contaminate cheese and pose a health risk if present.
• Common defects associated with spoiled cheese include gassy texture, butyric acid production, mold growth, bitterness, putrefaction and rancid odor, curd liquefaction, gelatinization, slime and mucous formation, off-flavors, and discoloration.
• Prevention of cheese spoilage involves maintaining proper hygiene and sanitation during cheese production, storage, and handling. Proper temperature control, adequate salting, and controlled ripening conditions are important for preventing microbial growth and spoilage.
• Regular monitoring of microbial quality, adherence to good manufacturing practices (GMP), and implementation of Hazard Analysis and Critical Control Points (HACCP) protocols are essential for preventing spoilage and ensuring the safety and quality of cheese.

In summary, the spoilage of cheese can be caused by various microorganisms, including bacteria, yeasts, and molds. Factors such as moisture content, pH, salinity, and ripening conditions influence the susceptibility of different types of cheese to spoilage. Proper hygiene, temperature control, and monitoring of microbial quality are essential for preventing spoilage and maintaining the quality and safety of cheese.

4. Spoilage of Yoghurt

Spoilage of yogurt refers to the deterioration in quality, flavor, and texture of yogurt due to the growth and activity of microorganisms. Here are some important points about the spoilage of yogurt:

• Yogurt is a lactic acid fermented milk product made using symbiotic cultures of Streptococcus thermophilus and Lactobacillus delbrueckii subsp. Bulgaricus.
• Fruits and nuts added to yogurt for flavor enhancement can be a potential source of contamination.
• Molds and yeasts are the main contaminants in yogurt.
• Common molds causing yogurt spoilage include Aspergillus, Penicillium, Rhizopus, Fusarium, and Trichoderma.
• Common yeasts causing yogurt spoilage include Candida spp., Debaryomyces, Kluyveromyces, Torulopsis, and Saccharomyces spp.
• These molds and yeasts can cause off-flavors, gas production, discoloration, and other undesirable changes in the yogurt.
• Their growth can lead to a decrease in acidity, resulting in proteolysis and putrefaction by bacteria.
• Some common foodborne pathogens that can be found in spoiled yogurt include Escherichia coli, Staphylococcus aureus, Listeria monocytogenes, and Yersinia enterocolitica.
• Prevention of yogurt spoilage involves maintaining good hygiene and sanitation during the production and handling of yogurt, including proper cleaning and sanitization of equipment and facilities.
• Proper temperature control during storage and distribution is crucial to inhibit the growth of spoilage microorganisms.
• Regular monitoring of microbial quality and adherence to good manufacturing practices (GMP) are important for preventing spoilage and ensuring the safety and quality of yogurt.

In summary, spoilage of yogurt can occur due to the growth of molds and yeasts, leading to changes in flavor, texture, and appearance. Proper hygiene, temperature control, and monitoring of microbial quality are essential to prevent spoilage and maintain the quality and safety of yogurt.

5. Spoilage of Ice-cream

Spoilage of ice cream refers to the deterioration in quality, flavor, and appearance of ice cream due to the growth and activity of microorganisms. Here are some important points about the spoilage of ice cream:

• Ice cream is a frozen milk product made by freezing a mixture of milk, cream, sugars, emulsifiers, stabilizers, and flavor-enhancing ingredients.
• Due to its high nutritive value, nearly neutral pH, and long storage duration, ice cream provides a favorable environment for microbial growth.
• Psychrotrophic bacteria, such as Pseudomonas, Flavobacterium, Alcaligenes, and Listeria monocytogenes, are the main culprits of ice cream spoilage. These bacteria can grow and multiply at refrigeration temperatures.
• Certain molds, including Aspergillus, Fusarium, Geotrichum, Mucor, Penicillium, and yeasts such as Zygosaccharomyces, Saccharomyces, and Cryptococcus, can also contribute to ice cream spoilage.
• Major foodborne pathogens like Listeria monocytogenes, Salmonella spp., and Escherichia coli can contaminate ice cream and pose a risk to consumers.
• Spoilage caused by microorganisms can result in various defects in ice cream, including bitterness, off-flavors, rancidity, greenish pigments, discoloration, and surface taints.
• Prevention of ice cream spoilage involves strict adherence to good manufacturing practices (GMP), including proper sanitation, hygiene, and maintenance of equipment and facilities.
• Temperature control during production, storage, and distribution is crucial to inhibit the growth of spoilage microorganisms.
• Regular monitoring of microbial quality, including testing for foodborne pathogens, is essential to ensure the safety and quality of ice cream.
• Proper packaging, labeling, and storage instructions can help consumers handle and store ice cream properly to prevent spoilage.

In summary, ice cream spoilage can occur due to the growth of psychrotrophic bacteria, molds, and yeasts, leading to defects in flavor, texture, and appearance. Following good manufacturing practices, implementing proper hygiene measures, and maintaining appropriate temperature control are essential for preventing spoilage and ensuring the safety and quality of ice cream.

FAQ

References

1. William C. Frazier; Fourth Edition.pdf (1995). Food Microbiology.
2. Dhakane, R. D., Shikshan, J., & Mandal, P. (2020). Spoilage and preservation of milk and milk products : A review. (December).
3. Singh, V., Kaushal, S., Tyagi, A., & Sharma, P. (2011). Screening of bacteria responsible for the spoilage of milk. J. Chem. Pharm. Res, 3(4), 348–350.
4. Marth H. Elmer, Steele L. James (2001), Applied Dairy Microbiology
5. Meshref Ams (2010)., Microbiological quality and safety of cooking butter in Beni-Suef governorate-Egypt.
6. Özer, B. (2014). Microbiology and biochemistry of yogurt and other fermented milk products. Dairy Microbiology and Biochemistry: Recent Developments, (July 2014), 167–213. https://doi.org/10.1201/b17297-11
7. Yellanki, S. (2017). A Short Review on Milk Spoilage. J of Food and Dairy Tech, 5(3), 1.
8. Cancino-Padilla, N., Fellenberg, M. A., Franco, W., Ibáñez, R. A., & Vargas-Bello-Pérez, E. (2017). Foodborne bacteria in dairy products: Detection by molecular techniques. Cien. Inv. Agr, 44(3), 215–229. https://doi.org/10.7764/rcia.v44i3.1811
9. Jay, J. M. (2000). Modern food microbiology Sixth edition.
10. Garnier, L., Valence, F., & Mounier, J. (2017). microorganisms Diversity and Control of Spoilage Fungi in Dairy Products: An Update. https://doi.org/10.3390/microorganisms5030042
11. Jerry O., O., Maduka V, A., Uchechukwu O, E., Kenneth I., O., O.O., O., Euslar N., O., … Boniface, O. (2016). Isolation of Bacteria Contaminants from Tetra Packed Yoghurt. IOSR Journal of Pharmacy and Biological Sciences, 11(4), 75–77. https://doi.org/10.9790/3008-1104027577
12. Kumar Verma, D., Mahato, D. Kumar, Billoria, S., Kapri, M., Prabhakar, P. K., Kumar V, A., & Prakash Srivastav, P. (2017). Microbial Spoilage in Milk and Milk Products: Potential Solution, Food Safety, and Health Issues. Microorganisms in Sustainable Agriculture, Food, and the Environment, (May 2017), 171–195. 7. https://doi.org/10.1201/9781315365824-6
13. Samaržija, D., Zamberlin, Š., & Pogačić, T. (2012). Psihrotrofne bakterije i njihovi negativni utjecaji na kvalitetu mlijeka i mliječnih proizvoda. Mljekarstvo, 62(2), 77–95.