Handbook of Food Science and Technology 3

Substrates 
The physicochemical properties of the curd vary with the manufacturing 
process. While the composition of the curd is well defined, its structure is 
more complex. It is difficult to control microbial growth and enzymatic action 
in such a complex and heterogeneous medium.
The kinetics of ripening depends on the mobility of carbohydrates, proteins 
and lipid substrates, reaction products (lactate, amino acids, fatty acids) in the 

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54 Handbook of Food Science and Technology 3 
cheese matrix, and the rate of biological reactions, which depends on the pH of 
the matrix and its water availability. Reactions are generally faster when the 
pH of the curd is close to neutral (optimal activity pH of flora and enzymes) 
and the MNFS is high. The shelf life of the product depends on the buffering 
capacity of the cheese, which limits and regulates the increase in pH 
(alkalinization) of the cheese during ripening (rennet curd and mixed curd with 
a predominantly rennet nature).
Ripening agents 
The enzymes involved in ripening have several origins: milk, coagulating 
agent and microorganisms in the cheese. 
Milk enzymes
– 
Plasmin
: heat resistant protease active in slow-ripened cooked and 
uncooked pressed cheeses. 
– 
Alkaline phosphatase
: denatured by pasteurization, it is active in raw 
milk cheeses only. 
– 
Lipase
: thermolabile enzyme active in raw milk cheeses only. It 
hydrolyzes short chain fatty acids in particular. Its action is more pronounced 
in goat’s and sheep’s milk because the proportion of short-chain fatty acids is 
higher and the fat globules are smaller than those of cow’s milk.
Coagulating enzymes
Rennet (mixture of chymosin and pepsin), a coagulating agent added to 
milk, has a wide spectrum of proteolytic activities. Its action is dominant in 
uncooked pressed cheeses. The reaction products formed are mainly high- 
molecular-weight peptides.
Enzymes of microbial origin 
These enzymes come from five main microbial groups: 
– 
Lactic acid bacteria
: present in the starter culture, convert lactose into 
lactic acid. They include: 
- 
lactococci
: dominant flora in uncooked soft and pressed cheeses; they 
produce lactic acid and exhibit proteolytic activity, 
- 
thermophilic streptococci and lactobacilli
: flora in cooked pressed 
cheeses; they exert acidifying and proteolytic activity, 

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From Milk to Dairy Products 55 
- 
Leuconostoc
: they produce aromatic components in addition to lactic 
acid and contribute to the open texture of blue cheese.
– 
Propionic bacteria
: produce propionic acid from lactate, are responsible 
for the open texture of cooked pressed cheeses and contribute to the formation 
of flavor and aroma. 
– 
Surface bacteria
: the most common are micrococci and coryneform 
bacteria (
Bacterium linens
); they are present in washed-rind and smear-ripened 
soft cheeses. They exhibit proteolytic and lipolytic activity.
–
Yeasts
: the most common is 
Geotrichum candidum
; it grows on the 
cheese surface by consuming lactic acid, producing ethanol and exhibiting 
lipolytic and proteolytic activity.
– 
Molds
: the two most common are 
Penicillium camemberti
, which is a 
surface mold on bloomy rind cheese, and 
Penicillium roqueforti
, an internal 
mold in blue cheeses. They have the most lipolytic enzymes, are responsible 
for the formation of methyl ketones and secondary alcohols, and also exhibit 
proteolytic activity.
Influence of ripening on the flavor of cheese
The development of flavor and aroma in cheese is based on a number of 
changes that occur during ripening (Figure 1.26). Several components, from 
various classes, are involved in this process (acids, alcohols, esters, sulfur 
products, etc.). Most of these compounds are found in all cheeses but in 
varying quantities and proportions: 
– in fresh cheeses, the flavor is based on acidity and acetaldehyde, which 
contributes to the fresh character of the cheese;
– in bloomy rind soft cheeses (Camembert), the main compounds are
1-Octen-3-ol, methyl ketones, secondary alcohols, phenolic compounds 
(phenylethanol and its esters), and various garlic-smelling volatile sulfur 
compounds;
– in washed-rind soft cheeses, (Limburger, Munster), surface bacteria 
(corynebacteria and micrococci) degrade amino acids and volatile fatty acids 
into sulphur compounds (methanethiol and thioesters); 
– in blue cheeses, there is a high proportion of free fatty acids, methyl 
ketones, secondary alcohols and lactones; 

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56 Handbook of Food Science and Technology 3 
– in semi-hard cheeses (cheddar), some authors attribute the aromatic base 
note to short-chain fatty acids (C
2 
to C
6
), methyl ketones and corresponding 
alcohols;
– in hard cheeses, where the level of proteolysis is high, the flavor is 
created by amino acids, acetic acid, propionic acid, alcohols, esters and sulfur 
products.