Emulsions, Microemulsions, and Lyotropic Liquid Crystals - Surface and Colloid Chemistry: Principles and Applications - page 208

heating, the buffer capacity of milk salts change, carbon dioxide is released, organic
acids are produced, and tricalcium phosphate and casein phosphate may be precipi-
tated with the release of hydrogen ions.
Age gelation is an aggregation phenomenon that affects shelf-stable, sterilized
dairy products, such as concentrated milk and UHT milk products. After weeks to
months of storage of these products, there is a sudden sharp increase in viscosity,
accompanied by visible gelation and irreversible aggregation of the micelles into
long chains forming a three-dimensional network. The actual cause and mechanism
is not yet clear; however, some theories exist.
Proteolytic breakdown of the casein : Bacterial or native plasmin enzymes that are
resistant to heat treatment may lead to the formation of a gel.
Chemical reactions: Polymerization of casein and whey proteins are due to
some kind of chemical reactions . The different proteins as found in the supernatant
of milk after precipitation at pH 4.6 are collectively called whey proteins. These
globular proteins are more water soluble than caseins and are subject to heat dena-
turation. Denaturation increases their water-binding capacity. The principal fractions
are β-lactoglobulin, α-lactalbumin, bovine serum albumin (BSA), and immunoglob-
ulins (Ig).
β- Lactoglobulins: (MW—18,000; 162 residues) This group, including eight genetic
variants, comprises approximately half the total whey proteins. β-Lactoglobulin
has two internal disulfide bonds and one free thiol group. Enzymes are a group of
proteins that have the ability to catalyze chemical reactions and the speed of such
reactions. The action of enzymes is very specific. Vitamins in milk emulsion are
one of the most important ingredients. Vitamins are organic substances essential to
many life processes. Milk includes fat-soluble vitamins A, D, E, and K. Vitamin A is
derived from retinol and β-carotene. Because milk is an important source of dietary
vitamin A, fat-reduced products that have lost Vitamin A with the fat are required
to supplement the product with Vitamin A. Milk is also an important source of the
following dietary water-soluble vitamins:

B1— t h ia m i ne
B2—riboflavin
B6—pyridoxine
B12—cyanocobalamin, niacin, pantothenic acid

The major vitamin content of fresh milk is as follows:

vitamin contents per liter

A (μg RE) 400

D (IU) 40

E (μg) 1000

K (μg) 50

B1 (μg) 450

B2 (μg) 1750

Niacin (μg) 900

B6 (μg) 500