Food Biochemistry and Food Processing

466 Part IV: Milk

• Secondary cultures: Most cheese varieties
  develop a secondary microflora, which was
  originally adventitious but now develops mainly
  from added cultures. Examples are
  Propionibacteria freudenrichiisubsp. shermanii
  (Swiss cheeses), Penicillium roqueforti(blue
  cheeses), P. camambertiand Geotrichium
  candidum(Camembert and Brie),
  Brevibacterium linens, Arthrobacterspp.,
  Corynebacteriumand yeasts (surface smear–
  ripened cheese), citrate-positive Lc. lactisand
  Leuconostocspp. (Dutch-type cheeses). Most of
  the microorganisms used as secondary cultures
  are very active metabolically and many secrete
  very active proteolytic and lipolytic enzymes.
  Consequently, they dominate the ripening of
  varieties in which they are used. Traditionally, a
  secondary culture was not used for Cheddar-type
  cheese, but it is becoming increasingly common
  to add an adjunct culture, usually mesophilic
  lactobacilli, to accelerate ripening, intensify
  flavor, and perhaps create tailor-made flavor.
  Essentially, the objective is to reproduce the
  microflora, and consequently the flavor, of raw-
  milk cheese.


• Exogenous enzymes: For some varieties of Italian
  cheese, e.g., provolone and pecorino varieties,
  rennet paste is used as coagulant. The rennet
  paste contains a lipase, pregastric esterase (PGE),
  in addition to chymosin; PGE is responsible for
  extensive lipolysis and the characteristic piquant
  flavor of the cheese. Rennet extract used for most
  varieties lacks PGE.

During ripening, a very complex series of reac-
tions, which fall into three groups, occur: (1) glycol-
ysis of lactose and modification and/or catabolism
of the resulting lactate, (2) lipolysis and the modifi-
cation and catabolism of the resulting fatty acids,
and (3) proteolysis and catabolism of the resulting
amino acids.

Glycolysis and Related Events Fresh cheese curd
contains about 1% lactose, which is converted to
lactic acid (mainly the L-isomer) by the starter LAB,
usually within 24 hours. Depending on the variety,
the L-lactic acid is racemized to DL-lactic acid by
NSLAB, or catabolized to CO 2 and H 2 O in mold-
ripened and in smear-ripened cheese. In Swiss-type
cheese, lactic acid is converted to propionic and
acetic acids, CO 2 , and H 2 O by P. freudenrichiisub-

sp. shermanii; the CO 2 is responsible for the charac-

teristic eyes in such cheeses.

Lipolysis Little lipolysis occurs in most cheese

varieties, in which it is catalyzed by the weakly lip-

olytic LAB or NSLAB, and indigenous milk lipase if

raw milk is used. Extensive lipolysis occurs in some

hard Italian-type cheeses, for example, provolone

and pecorino varieties, for which PGE is responsible,

and in blue cheese, for whichP. roquefortiis respon-

sible. Fatty acids are major contributors to the flavor

of provolone and pecorino cheeses, and some may be

converted to lactones or esters, which have character-

istic flavors. In blue-veined cheese, fatty acids are

converted to methyl ketones byP. roqueforti,and

these are mainly responsible for the characteristic

peppery taste of such cheeses. Some of the methyl

ketones may be reduced to secondary alcohols.

Proteolysis Proteolysis is the most complex and

probably the most important of the three primary

ripening reactions for the quality of cheese, espe-

cially internal bacterially ripened varieties. Initially,

the caseins are hydrolyzed by chymosin and, to a

lesser extent, by plasmin, in the case of 
-casein;

chymosin is almost completely inactivated in high-

cook varieties, and in this case plasmin is the pri-

mary agent of primary proteolysis. The polypeptides

produced by chymosin and plasmin are too large to

affect flavor, but primary proteolysis has a major

influence on the texture and functionality of cheese.

The peptides produced by chymosin and plasmin

are hydrolyzed to smaller peptides and amino acids

by proteinases and peptidases of starter LAB and

NSLAB. Small peptides contribute positively to the

background brothy flavor of cheese, but some are

bitter. Many amino acids also have a characteristic

flavor, but more importantly, they serve as substrates

for a great diversity of catabolic reactions catalyzed

by enzymes of LAB, NSLAB, and the secondary

culture. The flavor of internal bacterially ripened

cheese is probably due mainly to compounds pro-

duced from amino acids.

WHEY PROCESSING

RANGE OFWHEYPRODUCTS

For many centuries, whey was often viewed as an

unwanted and valueless by-product of cheese manu-

facture; however, since around 1970, whey has been