Food Biochemistry and Food Processing

10 Chymosin in Cheese Making 249

end products. A lively, almost translucent looking
cheese, after ripening several months, indicates ade-
quate rennet; an opaque, dull looking cheese indi-
cates inadequate amounts. Apparently, conversion to
peptides and later hydrolysis to smaller molecules
by bacterial enzymes give the translucent quality.
Residual rennet in cheese hydrolyzes alpha-s-1-
casein to alpha-s-1-I-casein, which leads to a desir-
able soft texture in the aged cheese (Lawrence et al.
1987).
Electrophoretic techniques (Ledford et al. 1966)
have demonstrated that in most ripening Cheddar
cheese from milk coagulated by rennet, para-beta-
casein largely remains intact while para-alpha-
casein is highly degraded. According to Fox et al.
(1993), if there is too much moisture in cheese or
too little salt, the residual chymosin will produce
bitter peptides due to excessive proteolysis. In
cheeses with high levels of beta-lactoglobulin, as in
cheeses made by ultrafiltration, proteolysis by resid-
ual chymosin is retarded because of partial inhibi-
tion of chymosin by the whey protein (Kosikowski
and Mistry 1997).
Edwards (1969) found that milk-coagulating en-
zymes from the mucors hydrolyze the paracaseins
somewhat similarly to rennet, while enzymes from
Cr. parasiticaand the papaya plant completely
hydrolyze para-alpha- and para-beta-caseins during
ripening.

Proteolytic activity of rennet substitutes, especial-

ly microbial and fungal substitutes, is greater than

that of chymosin. Cheese yield losses, though small,

do occur with these rennets. Barbano and Ras-

mussen (1992) reported that fat and protein losses to

whey were higher with Rh. mieheiand Rh. pusillus

compared with those for fermentation-derived chy-

mosin. As a result, the cheese yield efficiency was

higher with the latter than with the former two

microbial rennets.

EFFECT OF CHYMOSIN ON

CHEESE TEXTURE

The formation of a rennet curd is the beginning of

the formation of a cheese mass. Thus, a ripened

cheese assumes its initial biological identity in the

vat or press. This is where practically all of the criti-

cal components are assembled and the young cheese

becomes ready for further development.

Undisturbed fresh rennet curd is not cheese

because it still holds considerable amounts of water

and soluble constituents that must be removed

before any resemblance to a cheese occurs. This

block of curd is cut into thousands of small cubes.

Traditionally, this is done with wire knives (Fig.

10.2) but in large automated vats, built-in blades

rotate in one direction at a selected speed to system-

atically cut the curd. Then the whey, carrying with it

Figure 10.2.Cutting of rennet curd.