What are the most comprehensive compounds in milk?
o Primary flora of raw milk: Contamination at the level of the udder and the tip of the nipple.
o Contamination with cold-loving microorganisms: Through bedding, soil, water, plants.
o Contamination with coliforms: Soil, bedding.
o Contamination with spore-forming microorganisms: Bedding.
Main factors affecting milk contamination:
Milking equipment
Udder tissue
Environment
Secondary factors influencing milk contamination:
Temperature and time
Routine test for milk contamination:
Total bacterial count
Premium milk contains 30,000 microorganisms per cc.
Mastitis factors:
Streptococcus uberis, Galactiae, Disgalactiae
Nipple tissue is mostly contaminated with Staphylococcus and Streptococcus.
Mycobacterium lactinum is 100% resistant to pasteurization.
The most important bacillus in contamination is Bacillus licheniformis.
Bacillus is transferred through silage and bedding.
Cold-loving bacteria produce lipolytic and proteolytic enzymes during growth, which are heat-resistant.
Components in milk:
Water: 78.5%
Dry matter: 13%
Fat: 3.9%
Protein: 3.4%
Lactose: 4.8%
Due to the presence of a two-layer membrane around fat globules, the enzyme lipase cannot break them down.
Internal: Phospholipid, Glycoprotein
External: Membrane protein
Melting points of important milk fats:
Myristic acid (14-carbon): 54°C
Palmitic acid (16-carbon): 56°C
Stearic acid (18-carbon): 69°C
Oleic acid (18-carbon with double bond): 14°C
Using green fodder + cotton seed cake: Increased oleic acid and softening of butter.
Using woody fodder and sesame cake: Increased myristic, palmitic, stearic acids and hardening of butter.
The part of the amino acid that contains amine and carboxyl groups is hydrophilic.
Amphoteric property or isoelectric point in milk:
If acid or alkali is added, the pH does not change.
Types of milk proteins:
Caseins: 80%
Serum: 19%
Membrane: 5%
To separate casein proteins, we use acidification or proteolytic enzymes.
Serum proteins are heat-sensitive and denature quickly.
In protein structure, calcium, magnesium, and phosphoric acid are added to micelles.
Phosphoric acid gives proteins special consistency.
At the freezing temperature of milk (0.55°C), beta-caseins separate, resulting in soft cheese with high water content, which spoils quickly.
When acid is added to milk, calcium hydroxyl phosphate molecules change from an insoluble to a soluble form, and casein proteins reach the isoelectric state.
Rennet is a proteolytic enzyme that cuts kappa-casein between amino acids 105 (phenylalanine) and 106 (methionine).
Macropeptide: Amino acids from 106 to 169 that are cut by rennet from kappa-casein and fall into the whey.
Para kappa-casein: Amino acids from 1 to 105.
For whey protein precipitation, we use poly-electrolyte proteins (hydroxy-methyl cellulose) + pH and temperature change.
Whey protein:
Whey protein + macropeptides separated from casein protein.
Some whey proteins:
Alpha-lactalbumin: Precursor to lactase synthase enzyme.
Beta-lactalbumin: Only in cow’s milk, the main serum protein. When milk is heated, reactions occur between these two proteins and kappa-casein, and the enzyme cannot cut them.
Immunoglobulins: G1-G2-M-A
Immunoglobulin M plays the role of a clusterin or a binder of fat globules.
Lactoferrin: Found in low levels in cow’s milk, contains iron.
Proteose peptone: A type of pp3 unique to cows.
Albumin.
Once milk coagulates, it is irreversible.
Biocatalyst (enzyme) depends on two factors:
Temperature (ideal temperature 25-50)
and pH.
High temperatures (above 120) inactivate enzymes.
Alkaline phosphatase must be removed after pasteurization (pasteurization indicator for milk).
Milk enzymes:
Peroxidase: Produces oxidized substances with antimicrobial properties (LPS system).
Catalase.
Phosphatase: Breaks down alcohol and phosphoric acid compounds.
Lipase: Causes undesirable sharp flavors.
Protease: Causes bitter cheese flavor (the group that works in neutral and alkaline pH is called plasmin).
Membrane lipase is activated in cold, but serum lipase is activated by stirring, thermal changes, and homogenization.
For evaluating mastitis, catalase test is used.
In mastitis, the number of lymphocytes increases, and catalase produced by lymphocytes is high.
Lactose is formed by the union of glucose and galactose. It is the basis for fermentation industry and turns into lactic acid, which will make yogurt.
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