BLBS102-c23 BLBS102-Simpson March 21, 2012 13:44 Trim: 276mm X 219mm Printer Name: Yet to Come
23 Dairy Products 435Salting The salting step reduces the moisture content of the
curd, inhibits the growth of starter bacteria, and affects the flavor,
preservation, texture, and rate of ripening of the cheese. Final
salt contents of cheeses range from 0.7% to 4% (2–10% salt in
moisture contents). The amount of salt, the method for applica-
tion of the salt, and the timing of the salting is dependent on the
specific type of cheese. The salt may be incorporated through
(1) mixing with dry milled curd pieces, (2) rubbing onto the
surface of the molded cheese, or (3) immersing the cheese in a
salt brine. Following the salting step, the salt diffuses into the in-
terior of the cheese, with the subsequent displacement of whey.
Depending on the size of the cheese block and the composition
of the cheeses, it may take from 7 days to over 4 months for the
salt to equilibrate within the cheese.Ripening Fresh, green cheese has a bland flavor and a smooth,
rubbery texture. During the ripening process, the characteristic
texture and flavor of the cheese develop through a complex series
of biochemical reactions. Ripening starter cultures are selected
to develop the texture and flavor characteristics of the specific
cheese type. Enzymes released following lysis of the microor-
ganisms catalyze the degradation of proteins, lipids, and lactose
in the cheese to produce volatile flavor compounds, which con-
tribute to the characteristic flavor of the cheeses. As the ripening
time increases, the moisture content of the cheese decreases and
the intensity of the flavor increases. The resulting quality at-
tributes of the finished cheese depend on the initial composition
of the milk and the starter cultures used, the water activity of
the cheeses, and the temperature, time, and humidity during the
ripening period. Depending on the type of cheese, the ripening
period can range from 3 weeks to more than 2 years.
The ripening temperature influences the rate of the microbial
growth and enzyme activity during the process and the equilib-
rium between the biochemical reactions that occur during ripen-
ing. Ripening temperatures generally range from 5◦Cto20◦C,
which is well below the optimum temperatures for microbial
growth and enzyme activity. Soft cheeses are often ripened at
4 ◦C to slow the biochemical processes. An increase in ripening
temperature for hard cheeses reduces the ripening time necessary
for flavor development, with a 5◦C increase in ripening temper-
ature reducing the ripening time 2–3 months. However, caution
must be exercised in altering ripening temperatures since not all
microorganisms and enzymes respond to temperature changes
in the same manner, resulting in an imbalance in flavor charac-
teristics (Choisy et al. 2000).
The growth of most of the starter bacteria added to the milk
in the initial stages of cheese-making is slowed as the pH of
the cheese approaches 5.7 and following the addition of salt,
however fermentation and a decrease in pH continue. The fer-
mentation of lactose to lactic acid by the starter cultures pro-
vides an environment that prevents the growth of undesirable
microorganisms through the reduced pH and the formation of
an anaerobic environment. The reduced pH also has an influence
on activity of the proteases and lipases, which contribute to the
formation of critical volatile flavor compounds. The optimal ac-
tivity for proteases is between pH 5.5 and 6.5 and for lipases is
between pH 6.5 and 7.5. Lactose and citrate are precursors fora number of volatile flavor compounds, including diacetyl, ace-
toin, 2,3-butanediol, and acetaldehyde, which are also formed
during ripening (Urbach 1995).
Protease and lipase activity during the ripening is probably
most important to the development of the flavor and texture of
the cheese. Enzymes of the starter bacteria, nonstarter lactic acid
bacteria, and secondary cultures added during cheese-making
are most important in the development of the flavor and texture
of the cheese during ripening. These enzymes are released by
the lysis of the cell wall of the bacteria. Rennet enzymes and
endogenous milk enzymes, such as plasmin, also contribute to
these hydrolytic reactions during ripening. The extent of these
enzymatic reactions depends on the activity and specificity of
the enzymes, the concentration of the substrates, pH, water ac-
tivity, salt concentration, and ripening temperature and duration.
The degradation of the amino acids and fatty acids, through en-
zymatic and nonenzymatic reactions, results in the formation of
several important volatile flavor compounds, including sulfur-
containing compounds, amines, aldehydes, alcohols, esters, and
lactones.
Rennet and plasmin are associated with the primary phase
of proteolysis and hydrolyze the caseins to large polypeptides.
This proteolysis alters three-dimensional protein network of the
cheese to form a less firm and less elastic cheese. Although these
polypeptides do not have a direct impact on flavor, they do func-
tion as a substrate for the proteases associated with the starter
and nonstarter bacteria. However, if the primary proteolysis is
extensive, bitter peptides, with a high percentage of hydropho-
bic amino acids predominate. Free amino acids and short-chain
peptides contribute sweet, bitter, and brothy-like taste character-
istics to the cheese. Further degradation and chemical reactions
of these peptides and amino acids through the action of decar-
boxylases, transaminases, or deaminases, contribute to the for-
mation of amines, acids, ammonia, and thiols, which contribute
to cheese flavor.
Lipases break down triacylglycerols into free fatty acids, and
mono- and diacylglycerols. The short-chain free fatty acids con-
tribute to the sharp, pungent flavor characteristics of the cheese.
The degree of lipolysis that is acceptable without producing
soapy and rancid flavors depends on the type of cheese. Several
Penicilliumstrains form methyl ketones, lactones, and unsatu-
rated alcohols through their enzymatic systems associated with
β-oxidation and decarboxylation,β-oxidation and lactonization,
and lipoxygenase activity. Aliphatic and aromatic esters are syn-
thesized by esters present in a range of microorganisms, includ-
ing mesophilic and thermophilic lactic acid bacteria (Choisy
et al. 2000).
The texture of cheese is attributed to the three-dimensional
protein network, which entraps fat and whey. This structure is
altered through proteolysis during ripening to form a less firm
and less elastic cheese.
Carbon dioxide produced by the metabolism of the bac-
teria and entrapped within the curd results in the formation
of eyes in several types of cheeses. The small eyes char-
acteristics of Edam, Gouda, and related cheese varieties are
formed by carbon dioxide produced from citrate byLeuconos-
tocssp. In Swiss-type cheeses,Propionibacterium freudenreichii