Principles of Food Science and Nutrition
Unit II
Food microbiology with special reference to milk
Food microbiology is the study of microorganisms that inhabit, create, or contaminate food. Microorganisms can include bacteria, viruses, yeasts, moulds, and other fungi, and their presence in food can have both positive and negative effects.
Positive effects of microorganisms in food include the fermentation of food products such as yoghurt, cheese, and sourdough bread, which can improve flavour, texture, and nutritional value. On the other hand, the negative effects of microorganisms in food can include food spoilage, foodborne illness, and food poisoning.
Food microbiology plays a crucial role in food safety and preservation, as it helps identify and prevent the growth of harmful microorganisms in food. This involves the use of techniques such as sterilization, pasteurization, and food preservation methods like canning, drying, and freezing.
In the case of milk, food microbiology is particularly important due to its high nutrient content and potential for contamination with harmful microorganisms. Raw milk, for example, can be a source of foodborne illness if not properly pasteurized and can contain a range of bacteria and other microorganisms.
Milk is a nutrient-rich fluid that is produced by mammals, and it serves as an excellent growth medium for microorganisms. Milk is a complex food matrix that provides an ideal environment for the growth of various microorganisms, both beneficial and harmful.
The microorganisms that are commonly found in milk include bacteria, yeasts, and moulds. Some of these microorganisms are naturally present in milk, while others can contaminate it during handling and processing. Milk microbiology is particularly important because milk is consumed raw by infants and is also used as an ingredient in many food products.
Beneficial microorganisms such as lactic acid bacteria are used in the production of fermented milk products like yoghurt, cheese, and buttermilk. These bacteria ferment the lactose in milk to produce lactic acid, which helps to preserve the product by lowering the pH and inhibiting the growth of spoilage and pathogenic microorganisms.
However, pathogenic microorganisms such as Salmonella, Listeria, and Escherichia coli can also grow in milk and cause foodborne illness. These microorganisms can contaminate milk during milking, handling, and processing, and can survive and multiply under certain conditions such as inadequate refrigeration or pasteurization.
To ensure the safety and quality of milk and milk products, various microbiological tests are carried out on raw milk and finished products. These tests include total bacterial count, coliform count, and somatic cell count. The standard plate count (SPC) is a common test that measures the total number of bacteria in a milk sample. The coliform count is used as an indicator of fecal contamination, while the somatic cell count indicates the quality of milk produced by dairy animals.
In summary, milk is a complex food matrix that is susceptible to microbial contamination, both beneficial and harmful. Understanding the microbiology of milk is essential to ensure the safety and quality of milk and milk products.
Definition, and composition of milk and colostrum.
Milk
Milk is a white, nutrient-rich liquid produced by the mammary glands of mammals, primarily for the nourishment of their young.
It is a nutrient-rich food that contains proteins, carbohydrates, fats, vitamins, minerals, and water. Milk is the primary source of nutrition for young mammals, providing the necessary nutrients for growth and development.
In terms of its composition, milk is about 87% water and 13% solids. The solids include proteins (3.2-3.8%), fats (3.5-4.5%), lactose (4.5-5%), minerals (0.7-0.8%), and other components such as enzymes and vitamins. The composition of milk can vary depending on the species of mammal and the stage of lactation.
In addition to its nutritional value, milk is also used in a variety of food products such as cheese, butter, yoghurt, and ice cream. Milk can be pasteurized to kill harmful bacteria, homogenized to prevent separation of the cream, and fortified with additional vitamins and minerals to increase its nutritional value.
Different types of milk are available in the market, including cow's milk, goat's milk, sheep's milk, and buffalo milk. Cow's milk is the most commonly consumed type of milk and is a good source of protein and calcium. Goat's milk has a different taste and texture than cow's milk and is often used in specialty cheeses. Sheep's milk is higher in fat and protein than cow's milk and is used to make specialty cheeses and yoghurt. Buffalo milk is popular in some parts of the world, particularly in Asia, and is used to make traditional dairy products such as paneer and ghee.
Composition of Milk
Milk is a complex mixture of nutrients and other components necessary for the growth and development of young mammals. The exact composition of milk varies depending on the species of animal, as well as factors such as breed, age, diet, and stage of lactation. However, in general, the composition of milk can be broken down into the following major components:
- Water: Milk is about 87% water on average. The exact percentage varies depending on the species and stage of lactation.
- Proteins (3.2-3.8%): Milk contains several types of proteins, including casein and whey proteins. Casein makes up about 80% of the total protein content of milk, while whey proteins make up the remaining 20%. These proteins are essential for the growth and development of young mammals.
- Carbohydrates: The main carbohydrate in milk is lactose, which makes up about 4.8-5.2% of the milk by weight. Lactose is a disaccharide composed of glucose and galactose, and it provides an important source of energy for young mammals.
- Fats: Milk contains a complex mixture of fats, including saturated, monounsaturated, and polyunsaturated fatty acids. The fat content of milk varies depending on the species and stage of lactation, but it typically ranges from 3-4% in cow's milk to as much as 9% in seal milk.
- Vitamins: Milk is a good source of several vitamins, including vitamins A, D, and B12. These vitamins are important for the growth and development of young mammals, as well as for the maintenance of overall health.
- Minerals: Milk is also a good source of minerals, including calcium, phosphorus, and potassium. These minerals are essential for the development of strong bones and teeth, as well as for the proper functioning of the nervous and muscular systems.
Overall, the composition of milk is highly complex and can vary widely depending on several factors. Understanding the composition of milk is important for the production of dairy products, as well as for ensuring that young mammals receive the proper nutrients necessary for their growth and development.
Colostrum
Colostrum, also known as "first milk," is a specialized form of milk produced by female mammals in the first few days after giving birth. It is produced by mammals, including cows, goats, and humans, during the initial few days after giving birth. It is rich in nutrients, growth factors, and immune molecules, which are essential for the growth and development of newborns. Colostrum has a yellowish colour and a thicker consistency than regular milk. It is higher in protein, fat-soluble vitamins, minerals, and immunoglobulins than regular milk.
Colostrum is considered to be the first line of defence for the newborn against infections, as it contains high levels of immunoglobulins, particularly IgG. The immunoglobulins in colostrum are absorbed into the bloodstream of the newborn through the gut, providing passive immunity until the newborn's own immune system is fully functional. Colostrum also contains growth factors that stimulate the growth and development of organs and tissues, particularly the gastrointestinal tract.
Colostrum is collected from the cow during the first few milkings after giving birth. It is usually separated from regular milk and processed separately, as it is considered to be of higher value. Colostrum can be used for various purposes, including as a dietary supplement for humans and animals, as a source of immunoglobulins for medical use, and as an ingredient in animal feed. However, it is important to ensure that colostrum is collected and processed under hygienic conditions, as it can be a source of harmful bacteria if contaminated.
Composition
Colostrum is characterized by a higher concentration of nutrients and immunoglobulins compared to regular milk. The composition of colostrum can vary depending on several factors, including the species, breed, stage of lactation, and the health and nutrition of the mother.
Here is a breakdown of the composition of colostrum in detail:
- Water: The water content in colostrum ranges from 78-87%, depending on the species and stage of lactation.
- Proteins: Colostrum contains a higher concentration of proteins compared to regular milk. The main proteins in colostrum are immunoglobulins (IgG, IgA, IgM) (also known as antibodies), which provide passive immunity to the newborn. Other proteins found in colostrum include lactoferrin, which helps transport iron and has antimicrobial properties, and casein, a major milk protein. Lysozyme protein is also found.
- Carbohydrates: The carbohydrate content in colostrum is relatively low compared to regular milk. Colostrum contains lower levels of lactose than mature milk. Instead, it contains oligosaccharides, which are complex sugars that help promote the growth of beneficial bacteria in the gut.
- Lipids: The lipid content in colostrum is higher compared to regular milk. The lipids in colostrum are mainly in the form of triglycerides, which provide energy to the newborn. Colostrum also contains high levels of cholesterol and phospholipids.
- Minerals: Colostrum contains a higher concentration of minerals compared to regular milk, including calcium, magnesium, potassium, and sodium.
- Vitamins: Colostrum contains higher levels of vitamins A and E compared to regular milk.
- Growth factors: Colostrum contains various growth factors, including insulin-like growth factor 1 (IGF-1), which helps promote growth and development in newborns.
Overall, colostrum is a rich source of nutrients and immunoglobulins that provide passive immunity to the newborn. The composition of colostrum can vary depending on several factors, but it generally contains higher levels of proteins, lipids, minerals, and vitamins compared to regular milk.
Notes by Agricorn.in