Milk, a great source of nutrients including protein with all essential amino acids, essential
fatty acids, immunoglobulin and other micronutrients has become important part of diet to all
age group including pregnant Women. Most of the people in the world consume pasteurized
milk and few people prefer raw milk as they believe that raw milk is more beneficial, tastier
and convenient than pasteurized one. There is also abundancy in view that raw milk could
reduce allergic reactions and cure other ailments.
The microbial contamination of milk then after occurs within the udder, exterior of the udder
or from the surface of milk handling and storage equipment. Milk can also be cross
contaminated during food preparation and by infected workers who don’t practice good
hygiene. Pathogens involved in causing food borne diseases due to the consumption of raw
milk include Escherichia coli, Listeria monocytogenes, Salmonella, Staphylococcus aureus,
Bacillus cereus, Mycobacterium spp. and Clostridium botulinu Campylobacter, Brucella
abortus. Post-treatment contamination of milk caused outbreaks of campylobacteriosis,
salmonellosis, yersiniosis and staphylococcal enterotoxin “food poisoning”.
The presence of pathogenic bacteria in milk is the major public health concern resulting in
food borne illness.
Raw milk is unpasteurized and non-homogenized and is the one in which nothing has been
added, with all the natural enzymes, minerals & vitamins with all the necessary nutrients
present in it. However, it is understood that raw milk has dangerous bacteria which can pose a
serious health risk to anyone. It is not good for those with the weak immune systems,
pregnant women and even children.
Pasteurization is that the process of heating milk for a predetermined time at a predetermined
temperature to destroy pathogens. The thermal destruction process is logarithmic, and
bacteria are killed at a rate that’s proportional to the number of bacteria present.
Pasteurization improves a product’s safety and extends its time period by killing pathogenic
and rotting organisms. It was named after Louis Pasteur, who discovered that by applying
heat to wine at temperatures below its boiling point, spoilage microbes could also be
inactivated. Later, the technique was applied to milk, and it’s now the foremost important
step within the milk processing process. Pasteurization kills most disease-causing organisms
and prevents fermentation in milk, beer, and other liquids by sterilizing them partially or
completely. The Pasteurization process heats milk to 72 0 C for 15 seconds, inactivating or
killing organisms that grow rapidly in milk.
Organisms that grow slowly or produce spores aren’t destroyed by pasteurization. While
pasteurization kills many microorganisms in milk, inappropriate post-pasteurization handling
might contaminate milk again. There are two distinct purposes for the method of milk
i. The public health aspect-to make milk and milk products safe for human consumption by
destroying all bacteria which will be harmful to health.
ii. Keeping quality aspects-to improve the keeping quality of milk and milk products.
Psychrotrophic Bacteria in Milk
Psychrotrophic bacteria that spoil raw and milk are primarily aerobic gram-negative rods
within the family Pseudomonadaceae. Typically, 65 to 70% of psychrotrophic isolates from
milk are within the Pseudomonas. Although representatives of other genera, like Aeromonas,
Bacillus, Listeria, Staphylococcus, and Enterococcus, and therefore the Enterobacteriaceae
could also be present in milk and increase in number during storage, they are usually
outgrown by the gram-negative obligate aerobes when milk is held at a storage temperature
of 3 0 to 7°C.
The psychrotrophic spoilage microflora of milk is usually proteolytic, with many isolates
ready to produce extracellular lipases, phospholipase, and other hydrolytic enzymes but
unable to utilize lactose. The bacterium most frequently related to flavor defects in
refrigerated milk is Pseudomonas fluorescens, with Pseudomonas fragi, Pseudomonas putida,
and Pseudomonas lundensis also commonly encountered. Psychrotrophic bacteria commonly
found in milk are inactivated by pasteurization, but spores from aerobic bacteria like Bacillus
cereus could survive pasteurization temperatures and potentially pose a health risk.
Psychrotolerant bacteria, usually nonsporforming Gram-negative rods or Gram-positive spore
forming bacteria are the main cause of pasteurised milk spoilage. Gram-negative rods, such
as Pseudomonas spp., can spoil pasteurised milk if it is not heated properly or, more
frequently, postprocessing contamination. The term "pasteurised milk spoilage bacteria"
refers to a group of microorganisms that are not expected to survive the pasteurisation
process, including Staphylococcus spp., Streptococcus spp., or Acinetobacter,
Chryseobacterium, Psychrobacter, and Shingomonas spp. The most important factors for
determining milk quality preservation at low temperatures (10 °C) are postprocessing
Food spoilage due to post pasteurization contamination can be controlled by corrections in
pasteurization protocols and by improving good hygienic practices and sanitation.