Food Biochemistry and Food Processing

20

Biochemistry of Milk Processing

A. L. Kelly and P. F. Fox

453

Introduction
Thermal Processing of Milk
Introduction
Heat-Induced Changes in Milk Proteins
Stability of UHT Milk on Storage
Heat-Induced Changes in Lactose in Milk and the
Maillard Reaction
Inactivation of Enzymes on Heating of Milk
Changes on Evaporation and Drying of Milk
Concentration of Milk
Spray-Drying of Milk
Cheese and Fermented Milks
Introduction
Acid-Coagulated Cheeses
Fermented Milks
Acid-Heat Coagulated Cheeses
Rennet-Coagulated Cheeses
Coagulation
Acidification
Postcoagulation Operations
Ripening
Glycolysis and Related Events
Lypolysis
Proteolysis
Whey Processing
Range of Whey Products
Whey Protein–Rich Products
Lactose Processing
Milk Proteins: Isolation, Fractionation, and Applications
Recovery and Application of Caseins
Exogenous Enzymes in Dairy Processing

-galactosidase
Transglutaminase
Lipases
Milk Lipids

Production of Fat-Based Dairy Products

Lipid Oxidation

Ice Cream

Protein Hydrolysates

Infant Formulas

Novel Technologies for Processing Milk and Dairy

Products

Conclusion and Summary

References

INTRODUCTION

As described in Chapter 19, milk is a very complex

system; the continuous phase is an aqueous solution

of a specific sugar, lactose; globular (whey/serum)

proteins; inorganic salts; and hundreds of minor con-

stituents (e.g., vitamins) at trace levels. Dispersed in

the aqueous phase as an oil-in-water emulsion are

lipids in the form of small globules and a second,

unique, group of proteins, the caseins, which exist as

large colloidal particles, known as casein micelles,

with an average diameter of approximately 150 nm

(range 50–600 nm), that contain, on average, about

5000 protein molecules.

Owing to its physical state, milk is an unstable

system. The fat globules, which are less dense than

the aqueous phase, rise to the surface, where they

form a cream layer. The fat-rich cream can be skim-

med off and used for the manufacture of butter,

butter oil (ghee), or other fat-rich products. Alterna-

tively, the fat-depleted lower layer (skimmed milk)

may be run off, for example, through a valve at the

bottom of a separating vat. The skimmed milk may

Food Biochemistry and Food Processing

Edited by Y. H. Hui

Copyright © 2006 by Blackwell Publishing