MILK PROTEINS 21 1plastics, fibres or dye-binders for paper glazing. Although some casein is still
used for industrial applications, at least 80% of world production is now
used in foods. This change has occurred partly because cheaper and possibly
better materials have replaced casein for industrial applications while
growth in the production of fabricated foods has created a demand for
functional proteins at higher prices than those available for industrial-grade
products. Obviously, the production of a food-grade protein requires better
hygienic standards than industrial proteins; the pioneering work in this area
was done mainly in Australia and to a lesser extent in New Zealand in the
1960s.
Although heat-denatured whey protein, referred to as lactalbumin, has
been available for many years for food applications, it was of little signifi-
cance, mainly because the product is insoluble and therefore has limited
functionality. The commercial production of functional whey protein be-
came possible with the development of ultrafiltration in the 1960s. Whey
protein concentrates (WPCs) produced by ultrafiltration are now of major
commercial importance, with many specific food applications. Superior
whey protein products (whey protein isolates, WPI) are being produced on
a limited scale by chromatography, although their substantially higher cost
has limited their production.
As discussed in section 4.16, many of the whey proteins have interesting
biological and physical properties. It is now possible to isolate individual
whey proteins on a commercial scale in a relatively pure form; it is likely
that in the immediate future such purified whey proteins will be readily
available for specific applications.4.15.1 Industrial production of caseins
There are two principal established methods for the production of casein on
an industrial scale: isoelectric precipitation and enzymatic (rennet) coagu-
lation. There are a number of comprehensive reviews on the subject (e.g.
Muller, 1982; Fox, 1989; Mulvihill, 1992; Fox and Mulvihill, 1992) which
should be consulted for references.
Acid casein is produced from skim milk by direct acidification, usually
with HCI, or by fermentation with a Lactococcus culture, to c. pH 4.6. The
curds/whey are cooked to about 50°C, separated using inclined perforated
screens or decanting centrifuges, washed. thoroughly with water (usually in
counter-flow mode), dewatered by pressing, dried (fluidized bed, attrition or
ring dryers) and milled. A flow diagram of the process and a line diagram
of the plant are shown in Figures 4.36 and 4.37.
Acid casein is insoluble in water but soluble caseinate can be formed by
dispersing the casein in water and adjusting the pH to 6.5-7.0 with NaOH
(usually), KOH, Ca(OH), or NH, to produce sodium, potassium, calcium
or ammonium caseinate, respectively (Figure 4.38). The caseinates are