Microbial contamination in milk

The milk market requires and offers safe and high-quality products, preventing  a contamination source by good hygiene practices to reduce a possible exposure of  food-borne pathogens and chemical milk residues.

Dairy products can harbor a variety of organisms, including many zoonotic bacteria such as Brucella abortus, B. melitensis, Campylobacter jejuni, Escherchia coli, Listeria monocytogense, Mycobacterium bovis, M .tuberculosis, Salmonella, Staphylococcus aureus, and Yersinia enterocolitica ,which can cause serious disease, especially in children, pregnant women, elderly, and compromised individuals.

Many of the microbiological hazards associated with dairy products such as butter, cheese, and yoghurt are derived from the raw milk.

Generally, pathogenic microorganisms can contaminate raw milk in two ways. First, endogenous contamination occurs when milk is contaminated by a direct transfer of pathogens from the blood (systemic infection) of an infected animal into the milk, or via an infection in the udder. The second means by which fresh milk can be contaminated, known as exogenous contamination, occurs where milk is contaminated during or after collection by animal feces, the exterior of the udder and teats, the skin, and other environmental sources.

The initial microflora of raw milk reflects directly microbial contamination during production. The microflora in milk when it leaves the farm is determined by the temperature to which it has been cooled and the temperature at which it has been stored.

The infectious bovine mastitis in milk production is considered a disease with high economic impact reducing milk yield and the industrial dairy process and food safety. S. aureus and Streptococcus agalactiae are the most prevalent contagious pathogens in bovine mastitis from dairy herds around the world.

The bovine mastitis in dairy herds affects milk composition and somatic cells counts, serum protein, and proteolytic enzymes. Other undesirable milk mastitis conditions are bacterial toxins and abnormal proteins derived from inflammatory tissular response, which influence milk flavor and taste as well as milk product stability in the dairy process.

Pathogen like Staphylococcus aureus may be part of the resident microflora of the living animal, where as other pathogens such as Escherichia coli 0157:H7 or Salmonella spp. may originate from faecal contamination during initial milk collection. It can also be subjected to contamination during transport, storage and manufacturing processes.

A major cause of failure of processing and packaging systems is the development of biofilms on equipment surfaces. These communities of microorganisms develop when nutrients and water remain on surfaces between times of cleaning and reuse. Bacteria in biofilms are more resistant to chemical sanitizers than are the same bacteria in suspension.

In butter-making, bacterial contamination can come from unclean surfaces, the butter maker and wash water. Packaging materials, cups and leaves are also sources of contaminants. When butter is made on a larger processing scale, bacterial contamination can come from holding-tank surfaces, the churn and butter-handling equipment.
Microbial contamination in milk

Dairy by-products

In dairy industry butter and cheese are main products while buttermilk is by-product.

Buttermilk is fermented milk with characteristically sour taste. The tartness of buttermilk is due to the presence of acid in the milk.

Today it becomes common to produce cultured buttermilks from skim or whole milk. The culture most frequently used is Streptococcus lactis, perhaps also spp. cremoris.

The most significant by-product from dairy processing industry is whey, generated from the cheese-making process. Liquid whey is the part of milk that separates from the curd during cheeses production. Approximately 80% of the milk that is used to make cheese is converted to whey, or about 1 gal of whey per pound of cheese.

Once considered a waste product is now widely accepted to contain many valuable constituent.

A number of opportunities exist for the recovery or utilization of the lactose and protein content of whey. It can be fed to animals as is or dried and can also use for animal and human diets.

The components of whey include beta-lactoglobulin, alpha-lactalbumin, bovine serum albumin, lactoferrin, immunoglobulin, lactoperoxidase enzymes, glycomacropeptides, peptones, lactose and minerals.

Other dairy by products include:
*Casein is the solid residue obtained from rennet coagulation of defatted milk. By definition, it contains at least 80% protein.
*Dried skim milk is sometime used in starter diets due primarily to its excellent digestibly and amino acid balance. It protein content is about 34%.
Dairy by-products