Dairy Chemistry And Biochemistry

386 DAIRY CHEMISTRY AND BIOCHEMISTRY

given excellent results in cheesemaking trials on various varieties and are
now widely used commercially, although they are not permitted in some
countries. Significantly, they are accepted for use in vegetarian cheeses. The
gene for R. miehei proteinase has been cloned in A. oryzae; the resultant
product, Marzyme GM, is commercially available (Texel, Stockport, UK)
and is reported to be a very effective coagulant.

Coagulation of rennet-altered micelles. When c. 85% of the total u-casein

has been hydrolysed, the micelles begin to aggregate progressively into a gel

network. Gelation is indicated by a rapid increase in viscosity (q) (Figure

10.3). Coagulation commences at a lower degree of hydrolysis of rc-casein if

the temperature is increased, the pH reduced or the Ca2+ concentration

increased.

0 20 40 M) RO

I of visunlly ohxrvcd dolling time

Figure 10.3 Schematic representation of the rennet coagulation of milk. (a) Casein micelles with

intact ti-casein layer being attacked by chymosin (C); (b) rnicelles partially denuded of ti-casein;

(c) extensively denuded micelles in the process of aggregation; (d) release of macropeptides (+)

and changes in relative viscosity (B) during the course of rennet coagulation.