Chemistry Reference
In-Depth Information
5
Enzymes in dairy product manufacture
Barry A. Law
5.1
INTRODUCTION
The dairy foods sector of the food manufacturing industry is a traditional user of enzymes. The
best-known dairy enzyme preparation is, of course, rennet, a collective name for commercial
preparations containing acid proteases extracted from animal tissues.
1
These products clot
milk by removing a highly charged peptide fragment from
-casein on the surface of micellar
casein, the majority form of milk protein. Destabilized casein micelles aggregate and form
the structure of the milk clot that is then acidified by lactic cultures to make cheese curd.
2
Although this use of enzymes is the single most important in the dairy sector, modern
production methods have made possible other applications to meet changing needs and
priorities. For example, in the UK and USA the shortage of calves from which to source
traditional rennet has led to the development of enzyme production technology with yeasts
moulds and fungi as the primary source. Over half of the total milk coagulating enzymes
used in these regions are microbial in origin, mostly from genetically modified (GM) food
yeast and mould containing copies of the calf gene for the production of chymosin, the
main acid proteinase involved in milk clotting. The other main type of microbial rennet
(now called 'coagulant') is made from non-GM mould,
Rhizomucor miehei
. This topic of
coagulant production and use in the dairy industry will be described and discussed in detail
in this chapter.
In addition to the use of milk-clotting enzymes to make cheese, the dairy industry also
makes use of enzymes such as lipases, non-coagulant proteases, aminopeptidases, lactases,
lysozyme, lactoperoxidase and transglutaminase. Some of these applications are traditional
(lipase for flavour enhancement) whilst others are relatively new (lactose hydrolysis, acceler-
ated cheese ripening, control of microbiological spoilage, modification of protein function-
ality) and all will be discussed in detail below. Table 5.1 summarizes the range of enzymes
used in dairy products.
κ
5.2
MILK-CLOTTING ENZYMES
5.2.1 The nature and identity of rennets and coagulants
The first commercial standardized rennet preparation was made and sold by Chr. Hansen
A/S, Denmark in 1874, and was probably the first commercial enzyme of any type. It was
then, and still is by definition an extract of ruminant abomasum, ideally containing mainly
chymosin, the enzyme which is specific for
κ
-casein hydrolysis and casein destabilization.
