Introduction To Dairy Microbiology

- Coccus bacteria are spherical in shape (I).
- Bacillus bacteria are rod-shaped (II).
- Vibrio bacteria are curved rods (III).
- Spirillum bacteria are coiled threads (IV).
This classification is based on the morphology of bacterial cells, which is crucial for identification in microbiology.

Nisin is not a natural component of raw milk but is produced by bacterial fermentation. Lactoferrin, immunoglobulins, and lysozyme are naturally occurring inhibitory substances that help protect milk from microbial contamination.

Nisin is an antibacterial substance produced by *Lactococcus lactis ssp. lactis* during fermentation. It is effective against gram-positive bacteria and is widely used as a preservative in dairy products like cheese.

Bacteriocins such as nisin, pediocins, bifidin, and sakacins are widely used as bio-preservatives. These natural antimicrobial compounds inhibit the growth of spoilage and pathogenic microorganisms, enhancing food safety and shelf life.

Reuterin, a compound produced by *Lactobacillus reuteri*, is pH-neutral, water-soluble, and effective against a wide range of microbes. It is resistant to enzymes like nuclease, protease, and lipase, making it an excellent natural preservative for dairy and other food products.

Homofermentative lactic acid bacteria metabolize lactose primarily into lactic acid as the main end product. This process lowers the pH of milk, aiding in the preservation and coagulation required for products like yoghurt and cheese.

Late blowing in canned foods is caused by Clostridium foetidum, an anaerobic spore-forming bacterium. This microorganism produces gas during its metabolic activity, leading to bulging of the cans. Such defects not only spoil the food but can also pose serious health risks if consumed. Proper sterilization and hygiene during canning are essential to prevent this issue.

Most bacteria grow optimally in a neutral to slightly acidic environment. The pH range of 6.0 to 7.7 is ideal for bacterial growth in milk and milk products. This range corresponds to the natural pH of fresh milk, making it conducive to microbial activity. Beyond this range, either an acidic or alkaline environment inhibits bacterial growth. Monitoring pH levels in dairy products ensures their safety and helps in preventing spoilage.

The bifidus factor in human milk promotes the growth of *Lactobacillus bifidus*, a beneficial gut bacterium that helps in maintaining intestinal health and protecting infants against harmful pathogens. This factor enhances the germicidal properties of human milk by creating an acidic environment unfavorable for pathogenic bacteria. It plays a critical role in building an infant’s immunity.

Yellow pigmentation in the creamy layer of milk is caused by Pseudomonas synxantha. This bacterium produces pigments during its growth, leading to discoloration. Such microbial contamination can affect the sensory quality of milk and indicates poor hygiene during processing or storage.

The isoelectric pH of casein, the major protein in milk, is 4.6. At this pH, casein molecules lose their net charge, leading to aggregation and precipitation. This property is utilized in processes like cheese-making and acid coagulation of milk.