Microbial Spoilage of Milk and Milk Products (Cream, Butter, Cheese, Yoghurt, Ice-cream)
Milk is a complex biological fluid that contains various nutrients such as water, fat, protein, lactose, minerals, and vitamins. These nutrients make milk an ideal growth medium for many types of microorganisms, both beneficial and harmful. Microorganisms can affect the quality, safety, and shelf life of milk and its products. They can also contribute to the flavor, texture, and nutritional value of fermented milk products such as cheese, yogurt, and kefir.
The growth of microorganisms in milk depends on several factors such as:
- The initial microbial load of raw milk
- The type and level of contamination during milking, handling, processing, and storage
- The temperature and duration of storage
- The pH and water activity of milk and its products
- The presence of antimicrobial agents such as lactoperoxidase, lactoferrin, lysozyme, and immunoglobulins in milk
- The presence of inhibitors such as lactic acid, acetic acid, propionic acid, ethanol, carbon dioxide, and hydrogen peroxide produced by some microorganisms
- The presence of synergistic or antagonistic interactions among different microorganisms
The main groups of microorganisms that are associated with milk and its products are:
- Bacteria: They are the most abundant and diverse group of microorganisms in milk. They can be classified into different categories based on their morphology (cocci or rods), gram reaction (positive or negative), oxygen requirement (aerobic or anaerobic), spore formation (spore-forming or non-spore-forming), temperature preference (psychrotrophic or thermophilic), acid production (acidogenic or non-acidogenic), gas production (gasogenic or non-gasogenic), proteolysis (proteolytic or non-proteolytic), lipolysis (lipolytic or non-lipolytic), etc. Some examples of bacteria that are commonly found in milk and its products are Lactococcus, Lactobacillus, Streptococcus, Enterococcus, Leuconostoc, Pediococcus, Bifidobacterium, Propionibacterium, Staphylococcus, Bacillus, Clostridium, Escherichia coli, Salmonella, Listeria monocytogenes, Campylobacter jejuni, Yersinia enterocolitica, etc.
- Yeasts: They are unicellular fungi that can grow in aerobic or anaerobic conditions. They can ferment sugars to produce ethanol and carbon dioxide. They can also produce organic acids and volatile compounds that contribute to the flavor and aroma of some fermented milk products. Some examples of yeasts that are commonly found in milk and its products are Saccharomyces cerevisiae, Kluyveromyces lactis, Candida kefyr, Candida krusei, Candida albicans, Debaryomyces hansenii, Geotrichum candidum, Pichia fermentans, Rhodotorula mucilaginosa, Torulaspora delbrueckii, Zygosaccharomyces bailii, etc.
- Molds: They are multicellular fungi that grow as filamentous hyphae. They can produce spores that can be dispersed by air or water. They can also produce mycotoxins that can be harmful to human health. Some examples of molds that are commonly found in milk and its products are Aspergillus flavus, Aspergillus niger, Aspergillus ochraceus, Aspergillus parasiticus, Fusarium graminearum, Fusarium moniliforme, Fusarium oxysporum, Fusarium verticillioides, Penicillium camemberti, Penicillium roqueforti, Penicillium verrucosum, Rhizopus stolonifer, etc.
- Protozoa: They are single-celled eukaryotes that can move by flagella or cilia. They can cause parasitic infections in humans and animals. Some examples of protozoa that have been reported to contaminate milk and its products are Cryptosporidium parvum, Giardia lamblia, Toxoplasma gondii, etc.
In summary, milk is a rich source of nutrients for microorganisms that can affect its quality and safety. Therefore, proper hygiene and sanitation practices during milking, handling, processing, and storage are essential to prevent microbial spoilage and ensure the production of high-quality milk products.
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Milk is not sterile when obtained from animals. It can be contaminated by various sources during production, collection, processing, and distribution. The main sources of milk contamination are:
The milking animals: The animals that produce milk, such as cows, buffalo, sheep, and goats, can harbor microorganisms in their skin, hair, udder, and feces. These microorganisms can be transferred to the milk during milking or through contact with the animal`s environment. Some examples of microorganisms that can contaminate milk from the milking animals are Staphylococcus aureus, Streptococcus agalactiae, Mycobacterium bovis, Brucella spp., Salmonella spp., and Campylobacter jejuni.
The milking equipment and storage tanks: The equipment used for milking and storing milk can also be a source of contamination if they are not properly cleaned and sanitized. Microorganisms can form biofilms on the surfaces of the equipment and storage tanks, which can be difficult to remove. Biofilms can also protect microorganisms from heat and disinfectants. Some examples of microorganisms that can contaminate milk from the milking equipment and storage tanks are Pseudomonas spp., Bacillus spp., Listeria monocytogenes, Escherichia coli, and Enterobacter spp.
The water quality: The water used for washing the milking animals, the milking equipment, and the storage tanks can also introduce microorganisms into the milk if it is not of good quality. Water can be contaminated by sewage, animal waste, soil runoff, or industrial pollutants. Some examples of microorganisms that can contaminate milk from the water quality are Vibrio cholerae, Shigella spp., Cryptosporidium spp., and Giardia spp.
The animal feed: The feed given to the milking animals can also affect the microbial quality of the milk. Feed can be contaminated by molds, yeasts, bacteria, or toxins that can grow on it during storage or transportation. Some examples of microorganisms that can contaminate milk from the animal feed are Aspergillus spp., Fusarium spp., Clostridium botulinum, and Clostridium perfringens.
The air quality: The air in the farm and the processing plant can also carry microorganisms that can contaminate the milk. Air can be contaminated by dust, insects, rodents, birds, or human activities. Some examples of microorganisms that can contaminate milk from the air quality are Aspergillus spp., Penicillium spp., Cladosporium spp., and Bacillus spp.
The human factor: The people involved in the production, collection, processing, and distribution of milk can also be a source of contamination if they do not follow good hygiene practices. People can carry microorganisms on their hands, clothes, hair, or respiratory tract. They can also introduce microorganisms into the milk through coughing, sneezing, or touching. Some examples of microorganisms that can contaminate milk from the human factor are Staphylococcus aureus, Streptococcus pyogenes, Corynebacterium diphtheriae, and Escherichia coli.
These sources of milk contamination can introduce different types of microorganisms into the milk that can cause spoilage or disease. Therefore, it is important to control these sources and prevent microbial contamination of milk and its products.
Milk is composed of water, fat, protein, lactose, and various minerals and vitamins. These components provide a rich source of nutrients for many microorganisms that can cause spoilage of milk. The rate of spoilage depends on factors such as the number and species of the initial microflora, the storage temperature and conditions, and the presence of contaminants.
The most common spoilage of fluid milk products is souring caused by lactic acid bacteria that ferment lactose to produce lactic acid . This lowers the pH of milk and causes the casein proteins to coagulate, forming curd. The souring bacteria can be divided into two groups: thermoduric and psychrotrophic. Thermoduric bacteria are those that can survive pasteurization and grow at refrigeration temperatures, such as Streptococcus thermophilus, Lactobacillus delbrueckii subsp. bulgaricus, and some Enterococcus and Lactococcus species. Psychrotrophic bacteria are those that can grow at low temperatures (below 7°C), such as Pseudomonas, Flavobacterium, Alcaligenes, Listeria monocytogenes, Yersinia enterocolitica, some coliforms, and Bacillus spp. . These bacteria can also produce proteases and lipases that hydrolyze milk proteins and fats, resulting in bitterness, rancidity, and off-flavors.
Another type of spoilage of milk is sweet curdling caused by coliform bacteria such as Escherichia coli, Enterobacter aerogenes, Klebsiella pneumoniae, and Citrobacter freundii. These bacteria ferment lactose to produce gas (carbon dioxide and hydrogen) and organic acids (acetic, formic, and lactic). The gas production causes the milk to foam and swell, while the acid production lowers the pH and causes the casein to coagulate. However, unlike souring, the curd formed by sweet curdling is soft and slimy due to the presence of polysaccharides produced by the bacteria.
Other types of spoilage of milk include discoloration caused by pigmented bacteria such as Pseudomonas fluorescens (blue-green), Serratia marcescens (red), Flavobacterium spp. (yellow), Micrococcus luteus (yellow), and Chromobacterium violaceum (purple); gas production caused by clostridia such as Clostridium tyrobutyricum and Clostridium butyricum that ferment lactose to produce butyric acid and hydrogen; proteolysis caused by proteolytic bacteria such as Bacillus cereus, Bacillus subtilis, Clostridium sporogenes, Pseudomonas fragi, and some coliforms that degrade casein to produce peptides and amino acids; lipolysis caused by lipolytic bacteria such as Pseudomonas fluorescens biotype II, Pseudomonas putida biotype A, Staphylococcus aureus, Staphylococcus epidermidis, Corynebacterium spp., Micrococcus spp., Bacillus spp., Clostridium spp., Mucor spp., Penicillium spp., Aspergillus spp., Rhizopus spp., Geotrichum candidum, Candida lipolytica, Torulopsis glabrata, Saccharomyces cerevisiae that hydrolyze milk fat to produce free fatty acids; and ropiness caused by ropy bacteria such as Alcaligenes viscolactis, Enterobacter aerogenes, Klebsiella pneumoniae that produce extracellular polysaccharides that give milk a viscous or slimy consistency.
Some microorganisms that cause spoilage of milk can also be pathogenic to humans. These include Listeria monocytogenes (causing listeriosis), Yersinia enterocolitica (causing yersiniosis), Salmonella spp. (causing salmonellosis), Escherichia coli O157:H7 (causing hemorrhagic colitis and hemolytic uremic syndrome), Campylobacter jejuni (causing campylobacteriosis), Brucella spp. (causing brucellosis), Mycobacterium bovis (causing tuberculosis), Staphylococcus aureus (producing enterotoxins), Bacillus cereus (producing emetic and diarrheal toxins), Clostridium botulinum (producing botulinum toxin), Clostridium perfringens (producing enterotoxin), Cryptosporidium parvum (causing cryptosporidiosis), Giardia lamblia (causing giardiasis), Toxoplasma gondii (causing toxoplasmosis), Trichinella spiralis (causing trichinellosis), Taenia saginata (causing taeniasis), Echinococcus granulosus (causing echinococcosis), Coxiella burnetii (causing Q fever), Streptococcus agalactiae (causing neonatal sepsis and meningitis) .
To prevent or reduce the spoilage of milk by microorganisms, various methods are used such as pasteurization, ultra-high temperature treatment, ultrafiltration, high-pressure processing, pulsed electric field treatment
Pasteurization is a process of mild heating that kills or deactivates microorganisms that cause spoilage or disease in foods and beverages . It is named after Louis Pasteur, who demonstrated the effect of heat on wine and beer in the 1860s . Pasteurization does not sterilize products, as it does not destroy bacterial spores . The temperature and duration of pasteurization vary depending on the type of product and the target pathogens .
Pasteurization of milk, widely practiced in several countries, notably the United States, requires temperatures of about 63 °C (145 °F) maintained for 30 minutes or, alternatively, heating to a higher temperature, 72 °C (162 °F), and holding for 15 seconds (and yet higher temperatures for shorter periods of time). The times and temperatures are those determined to be necessary to destroy Mycobacterium tuberculosis and other, more heat-resistant, non-spore-forming, disease-causing microorganisms found in milk. The treatment also destroys most of the microorganisms that cause spoilage and so prolongs the storage time of food.
Ultra-high-temperature (UHT) pasteurization involves heating milk or cream to 138–150 °C (280–302 °F) for one or two seconds. Packaged in sterile, hermetically sealed containers, UHT milk may be stored without refrigeration for months. Ultrapasteurized milk and cream are heated to at least 138 °C for at least two seconds, but, because of less stringent packaging, they must be refrigerated. Shelf life is extended to 60–90 days. After opening, spoilage times for both UHT and ultrapasteurized products are similar to those of conventionally pasteurized products.
The main components of milk are water, fat, protein, and lactose. Its high water activity, moderate pH (6.4–6.6), and high nutrient content make milk an excellent medium for microbial growth. Both raw milk and pasteurized milk contain many types of microorganisms, they are refrigerated, yet they have limited shelf life. During refrigerated storage (at dairy farms and processing plants) before pasteurization, only psychrotrophs can grow in refrigerated milk storage such as Pseudomonas, Flavobacterium, Alcaligenes, Listeria monocytogenes, Yersinia enterocolitica, some coliforms, and Bacillus spp. Those that spoil milk after heating are the thermoduric microorganisms surviving pasteurization such as Micrococcus, some Enterococcus, Streptococcus, some Lactobacillus, and spores of Bacillus and Clostridium. Molds and yeasts are usually eliminated during the pasteurization process therefore they cause milk spoilage after the heat treatment such as Aspergillus, Byssochlamys, Cladosporium, Candida spp.
Pasteurization should destroy pathogenic bacteria, yeast, mold, and most of the living microorganisms that can be found in raw milk, generally resulting in improved milk safety. However, some pathogens may survive pasteurization if they are present in high numbers or if they have developed heat resistance. For example, some strains of Salmonella, Escherichia coli O157:H7, and Listeria monocytogenes have been reported to survive pasteurization under certain conditions. Therefore, proper hygiene practices during milking, handling, processing, packaging, and storage are essential to prevent post-pasteurization contamination and ensure food safety.
Due to the mild heat treatment, there are minor changes to the nutritional quality and sensory characteristics of the treated foods. Pasteurization may cause some loss of vitamins B1, B6, B12, C, E and folate in milk due to oxidation or thermal degradation. However, these losses are usually small compared to the natural variation in milk composition and the effects of storage conditions. Pasteurization may also affect some proteins in milk such as whey proteins and casein micelles by causing denaturation or aggregation. This may alter the functional properties of milk such as solubility, viscosity, gelation, foaming, and emulsification. Pasteurization may also affect the flavor and color of milk by causing Maillard browning reactions between lactose and amino acids or by oxidizing fat components.
Pasteurization is a widely used method to improve the safety and shelf life of milk and other foods. It involves heating the food to a specific temperature for a specific time to kill or deactivate most microorganisms that cause spoilage or disease. However, it does not sterilize the food completely and some microorganisms may survive or contaminate the food after pasteurization. Therefore, proper hygiene practices throughout the food chain are important to ensure food quality and safety. Pasteurization may also cause some changes in the nutritional and sensory properties of the food due to heat-induced reactions. These changes are usually minor compared to the benefits of pasteurization.
Milk products are derived from milk by various processes such as separation, churning, coagulation, fermentation, and freezing. Depending on the type and quality of the milk product, different microorganisms may cause spoilage and defects. Some of the common milk products and their spoilage are discussed below:
Cream is the fat-rich layer of milk that is separated by skimming or centrifugation. Cream can be classified by its fat content and heat treatment, such as single, double, whipping, pasteurized, sterilized, or UHT cream. Cream is highly susceptible to microbial spoilage due to its high nutrient content and moderate pH. The main sources of contamination are the raw milk, the equipment, and the environment.
The main spoilage microorganisms in cream are psychrotrophic bacteria such as Pseudomonas, Flavobacterium, Alcaligenes, Acinetobacter, Aeromonas, and Achromobacter . These bacteria can produce proteolytic and lipolytic enzymes that cause bitterness, rancidity, off-flavors, and gas production in cream. At room temperature, other bacteria such as Corynebacterium, Bacillus, Micrococcus, Lactobacillus, and Staphylococcus can also spoil cream. Molds and yeasts can cause surface taints and discoloration in cream.
Cream can also harbor pathogenic microorganisms such as Escherichia coli, Salmonella Typhimurium, and Listeria monocytogenes . These pathogens can cause foodborne illnesses if the cream is consumed raw or inadequately heated.
Butter is a milk product made by churning the cream to separate the butterfat from the buttermilk. Butter can be classified by its fat content, salt content, and flavoring agents. Butter is also prone to microbial spoilage due to its high fat content and water activity. The main source of contamination is the cream used for butter production.
The primary spoilage microorganisms in butter are molds such as Thamnidium, Cladosporium, Aspergillus . These molds can produce mycotoxins and cause discoloration and off-flavors in butter. Some psychrotrophic bacteria such as Pseudomonas spp. can also cause rancidity and surface stains in butter . Yeasts can cause gas production and fermentation in butter.
Butter can also contain pathogenic microorganisms such as Listeria monocytogenes, Brucella spp., Mycobacterium spp., Campylobacter jejuni, Yersinia enterocolitica, and Salmonella Typhimurium . These pathogens can survive pasteurization and refrigeration and cause serious infections if the butter is consumed raw or contaminated after processing.
Cheese is a fermented milk product that is made by coagulating the casein in milk using rennet or acid. Cheese can be classified by its moisture content, texture, ripening method, flavoring agents, and origin. Cheese undergoes ripening by the action of various microorganisms that contribute to its flavor, texture, and aroma. Cheese is also subject to microbial spoilage due to its high protein content and water activity. The main sources of contamination are the raw milk, the starter cultures, the equipment, and the environment.
The bacterial cheese spoilage is caused by Clostridium spp., (especially C. pasteurianum, C. butyricum, C. sporogenes, and C. tyrobutyricum), Bacillus polymyxa, Flavobacterium, Pseudomonas spp., Alcaligenes, and Achromobacter . These bacteria can produce gas, acid, proteolysis, lipolysis, and off-flavors in cheese. Yeasts are common cheese spoilage organisms e.g. Candida spp., Debaryomyces hansenii, Geotrichum candidum, and Pichia spp. . These yeasts can cause fermentation, discoloration, and surface defects in cheese. The mold spoilage in cheese is caused mainly by Penicillium spp. and Cladosporium spp. . These molds can produce mycotoxins and cause blue-green spots and musty odors in cheese.
Cheese can also harbor pathogenic microorganisms such as Listeria monocytogenes, Salmonella spp., Escherichia coli . These pathogens can survive pasteurization and ripening and cause food poisoning if the cheese is consumed raw or contaminated after processing.
Yoghurt is a lactic acid fermented milk product that is produced by using symbiotic cultures of two lactic acid bacteria (Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus). Yoghurt can be flavored with fruits, nuts, sugar, or other ingredients. Yoghurt is a nutritious food that has health benefits due to its probiotic bacteria. Yoghurt is also vulnerable to microbial spoilage due to its high moisture content and moderate pH. The main sources of contamination are the raw milk, the starter cultures, the flavoring ingredients, the equipment, and the environment.
Molds and yeasts are the primary contaminants in yoghurt . The most common mold causing yoghurt spoilage are Aspergillus, Penicillium, Rhizopus, Fusarium, and Trichoderma . These molds can produce mycotoxins and cause off-flavor, gas production, discoloration, etc. The most common yeasts causing yoghurt spoilage are Candida spp., Debaryomyces, Kluyveromyces, Torulopsis, and Saccharomyces spp. . These yeasts can cause fermentation, alcohol production, carbon dioxide production, etc. Molds and yeasts that cause yoghurt spoilage leads to a decrease in acidity, leading to proteolysis and putrefaction by bacteria.
Yoghurt can also contain pathogenic microorganisms such as Escherichia coli, Staphylococcus aureus, Listeria monocytogenes, and Yersinia enterocolitica . These pathogens can cause foodborne illnesses if the yoghurt is consumed raw or inadequately heated.
Ice-cream is a frozen milk product produced by freezing a pasteurized mixture of milk, cream, milk solids other than fat, sugars, emulsifier, and stabilizers. Ice-cream includes various flavor-enhancing ingredients like nuts, fruit pulp, confectionary products, eggs, and egg products. Ice-cream serves as a good medium for microbial growth due to its high nutritive value almost neutral pH and long storage duration . The main sources of contamination are the raw milk the flavoring ingredients the equipment and the environment.
The main spoilage microorganisms in ice-cream are psychrotrophic bacteria such as Pseudomonas Flavobacterium Alcaligenes Listeria monocytogenes . These bacteria can produce proteolytic lipolytic enzymes that cause bitterness rancidity off-flavors greenish pigments in ice-cream. Certain molds such as Aspergillus Fusarium Geotrichum Mucor Penicillium and yeasts such as Zygosaccharomyces Saccharomyces Cryptococcus also cause ice-cream spoilage^4^. These molds and yeasts can produce mycotoxins discoloration surface taints in ice-cream.
Ice-cream can also harbor pathogenic microorganisms such as Listeria monocytogenes Salmonella spp. Escherichia coli^4^. These pathogens can survive pasteurization freezing refrigeration and cause serious infections if the ice-cream is consumed raw or contaminated after processing.
Microbial spoilage of milk and milk products can result in various defects that affect the quality, safety, and sensory attributes of the products. Some of the common defects caused by microbial spoilage are:
Off-flavors: Microorganisms can produce unpleasant flavors in milk and milk products by metabolizing milk components such as lactose, fat, and protein. For example, some psychrotrophic bacteria can produce rancid, bitter, or fruity flavors by hydrolyzing milk fat and producing volatile fatty acids . Some thermoduric bacteria can produce burnt or caramel flavors by reducing lactose to galactose and glucose. Some molds and yeasts can produce musty, earthy, or alcoholic flavors by producing volatile compounds such as geosmin, 2-methylisoborneol, and ethanol .
Discoloration: Microorganisms can cause changes in the color of milk and milk products by producing pigments or altering the natural pigments present in the products. For example, some Pseudomonas spp. can produce blue-green pigments such as pyocyanin and fluorescein that cause blue milk. Some Bacillus spp. can produce yellow or brown pigments that cause yellowing or browning of milk. Some molds such as Penicillium spp. can produce green, blue, or black spores that cause discoloration of cheese.
Gas production: Microorganisms can produce gas in milk and milk products by fermenting lactose or other carbohydrates present in the products. For example, some coliforms such as Escherichia coli and Enterobacter spp. can produce carbon dioxide and hydrogen that cause gassy fermentation of milk. Some Clostridium spp. such as C. tyrobutyricum and C. butyricum can produce carbon dioxide, hydrogen, and butyric acid that cause late blowing of cheese. Some yeasts such as Saccharomyces spp. and Zygosaccharomyces spp. can produce carbon dioxide that cause swelling of yogurt containers.
Lactic acid production/Souring: Microorganisms can produce lactic acid in milk and milk products by fermenting lactose or other sugars present in the products. For example, some lactic acid bacteria such as Streptococcus thermophilus and Lactobacillus bulgaricus can produce lactic acid that causes desirable souring of yogurt. However, some thermoduric lactic acid bacteria such as Streptococcus lactis and Leuconostoc spp. can produce lactic acid that causes undesirable souring of pasteurized milk. Some Clostridium spp. such as C. pasteurianum and C. sporogenes can produce lactic acid that causes sour curdling of cream.
Proteolysis: Microorganisms can degrade protein in milk and milk products by producing proteases or peptidases that hydrolyze casein or other proteins present in the products. For example, some psychrotrophic bacteria such as Pseudomonas spp. and Bacillus spp. can produce proteases that cause gelation, bitterness, or ropiness of milk . Some lactic acid bacteria such as Lactobacillus casei and Lactococcus lactis subsp. cremoris can produce peptidases that cause flavor development or texture changes in cheese. Some molds such as Mucor spp. and Rhizopus spp. can produce proteases that cause softening or liquefaction of cheese.
Lipolysis: Microorganisms can degrade fat in milk and milk products by producing lipases or esterases that hydrolyze triglycerides or other lipids present in the products. For example, some psychrotrophic bacteria such as Pseudomonas spp., Alcaligenes spp., and Flavobacterium spp. can produce lipases that cause rancidity or bitterness of cream, butter, or cheese . Some molds such as Penicillium roqueforti and Geotrichum candidum can produce lipases that cause flavor development or texture changes in cheese. Some yeasts such as Candida lipolytica and Torulopsis colliculosa can produce esterases that cause fruity flavors in cheese.
Sweet curdling: Microorganisms can cause sweet curdling of milk by producing rennet-like enzymes that coagulate casein without producing acid. For example, some Bacillus spp., Alcaligenes spp., Flavobacterium spp., Corynebacterium spp., Micrococcus spp., Streptococcus faecalis var liquefaciens, and Lactobacillus casei subsp alactosus can produce rennet-like enzymes that cause sweet curdling of pasteurized milk .
Milk and milk products are highly nutritious foods that provide many health benefits to consumers. However, they are also prone to microbial spoilage due to their high water activity, moderate pH, and rich nutrient content. Microbial spoilage can cause various defects in milk and milk products such as off-flavors, discoloration, gas production, souring, proteolysis, lipolysis, and sweet curdling. Moreover, some microorganisms can cause food-borne illnesses and infections in humans.
To prevent or minimize microbial spoilage of milk and milk products, several measures can be taken such as:
- Maintaining good hygiene and sanitation practices at all stages of production, processing, packaging, storage, and distribution of milk and milk products.
- Using high-quality raw materials and ingredients that are free from contamination or have low microbial load.
- Applying appropriate heat treatment such as pasteurization or sterilization to kill or inactivate most of the spoilage and pathogenic microorganisms.
- Refrigerating or freezing milk and milk products to slow down or stop the growth of psychrotrophic microorganisms.
- Adding preservatives or antimicrobial agents such as salt, sugar, acidulants, nitrates, nitrites, sorbates, benzoates, propionates, etc. to inhibit the growth of microorganisms.
- Using starter cultures or probiotics to enhance the flavor, texture, and shelf life of fermented milk products such as cheese and yogurt.
- Educating consumers about the proper handling and storage of milk and milk products to avoid cross-contamination and temperature abuse.
By following these measures, the quality and safety of milk and milk products can be ensured and the spoilage losses can be reduced. Milk and milk products are valuable sources of nutrition and enjoyment for people of all ages and cultures. Therefore, it is important to protect them from microbial spoilage and preserve their freshness and wholesomeness.
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