Food Biochemistry and Food Processing (2 edition)

BLBS102-c25 BLBS102-Simpson March 21, 2012 13:23 Trim: 276mm X 219mm Printer Name: Yet to Come

25 Biochemistry of Milk Processing 475

Figure 25.3.Summary of amino acid catabolism during cheese ripening. MGL, methionine-γ-lyase; CBL, cystathionine-β- lyase; CGL,

cystathionine-γ-lyase; TPL, tyrosine-phenol lyase; aldDH, aldehyde dehydrogenase; KADH,α-keto acid dehydrogenase; HADH, hydroxyl acid

dehydrogenase;α−KADC,α−keto acid decarboxylase. (From Curtin and McSweeney 2004).

varieties. Initially, the caseins are hydrolysed by chymosin and,

to a lesser extent by plasmin, in the case ofβ-casein; chymosin is

almost completely inactivated in high-cook varieties and in this

case plasmin is the principal agent of primary proteolysis. The

polypeptides produced by chymosin or plasmin are too large to

affect flavour, but primary proteolysis has a major influence on

the texture and functionality of cheese. The peptides produced

by chymosin or plasmin are hydrolysed to smaller peptides and

amino acids by proteinases and peptidases of starter LAB and

NSLAB. Small peptides contribute positively to the background

brothy flavour of cheese but some are bitter. Many amino acids

also have a characteristic flavour but, more importantly, they

serve as substrates for a great diversity of catabolic reactions

catalysed by enzymes of LAB, NSLAB and the secondary

culture. The flavour of internal bacterially ripened cheese is

probably mainly due to compounds produced from amino acids

(Fig. 25.3).

Acceleration of Cheese Ripening

As the cost of storing cheese under controlled conditions for

ripening represents a significant proportion of the cost of man-

ufacturing cheese, there have been many studies on factors that

could accelerate the process of cheese ripening, that is achieve

the desired texture and flavour in a shorter time. Key strategies

that have been studied include increasing ripening temperature,

manipulating starter or adding adjunct starter culture (e.g., in-

creasing level of addition, or accelerating the rate at which starter

cells lyse and release their enzymes into the cheese curd) and

use of exogenous enzymes. Of these, the simplest is increas-

ing ripening temperature (e.g., from 7◦C for Cheddar to 13◦C),

which has been shown to increase rates of lipolysis and proteol-

ysis. For the use of exogenous enzymes, the key is to get even

distribution of enzyme in the cheese, which can most easily be

achieved by adding enzymes to the cheese milk; however, much

of the added enzyme is then lost in the whey. A general consid-

eration applying to all methods for accelerating cheese ripening

is that the overall balance of flavour should remain comparable

to the reference product, which can be difficult to achieve.

Cheese-Related Products

In addition to the many types of natural cheese, as introduced

previously, there is also a range of cheese-derived or substitute