534 10 Milk and Dairy Products
ty acids, especially those that affect cheese
aroma, depends on the specificity of the lipases
(Table 10.31). In addition to free fatty acids,
2-alkanones and 2-alkanols are formed as by-
products of theβ-oxidation of the fatty acids
(cf. 3.7.5).
Molds, particularlyPenicillium roqueforti, utilize
β-ketoacyl-CoA deacylase (thiohydrolase) and
β-ketoacid decarboxylase to provide the com-
pounds typical for the aroma of semi-soft cheeses
e. g., the blue-veined cheese (Roquefort, Stilton,
Gorgonzola, cf. Table 10.32).
Protein degradation to amino acids occurs
through peptides as intermediary products. De-
pending on the cheese variety, 20–40% of casein
is transformed into soluble protein derivatives, of
which 5–15% are amino acids. A pH range of 3–6
is optimum for the activity of peptidases from
Penicillium roqueforti. Proteolysis is strongly
influenced by the water and salt content of the
cheese. The amino acid content is 2.8–9% of
the cheese solids. Of the amino acids released,
glutamic acid is of special importance to cheese
taste (cf. 10.3.5). Ripening defects can produce
bitter-tasting peptides.
The amino acids are transformed further. In early
stages of cheese ripening, at a lower pH, they
are decarboxylated to amines. In later stages, at
a higher pH, oxidation reactions prevail:
Table 10.31.Substrate specificity of a lipase fromPeni-
cillium roqueforti
Substrate Hydrolysis (Vrel)
Tributyrin 100
Tripropionin 25
Tricaprylin 75
Tricaprin 50
Triolein 15
Table 10.32.2-Alkanones in blue cheese
2-Alkanone mg/100 g
na cheese (dry matter)
30 .5–0. 8
51 .4–4. 1
73 .8–8. 0
94 .4–17. 6
11 1 .2–5. 9
aNumber of C-atoms.
(10.18)Proteolysis contributes not only to aroma forma-
tion, but it affects cheese texture. In overripening
of soft cheese, proteolysis can proceed almost to
liquefaction of the entire cheese mass.
The progress of proteolysis can be followed by
electrophoretic and chromatographic methods,
e. g., via the peptide pattern obtained with the
help of RP-HPLC (Fig. 10.29) and via changes in
concentration of individual peptides which cor-
respond to certain casein sequences (Table 10.33)
and can serve as an indicator of the degree of
cheese ripening.
The decarboxylation of amino acids (name in
brackets) leads to the biogenic amines phenyl-
ethylamine (phenylalanine), tyramine (tyrosine),
tryptamine (tryptophan), histamine (histidine),
putrescine (ornithine) and cadaverine (lysine).
The content of these compounds in some types of
cheese is presented in Table 10.34. These values
can fluctuate greatly depending on the degree
of ripening. On average, 350–500 μmol per
person per day are consumed. Apart from cheese,Table 10.33.Amino acid sequences of some small pep-
tides from Cheddar cheese
Pep- Sequence Corresponding
tidea casein sequence30 APFPE αs1B 26–30b
37 D K I (H) P F βA^2 47–52
39 L P Q E (V L) αs1B 11–16
46 LQDKI(H)P(F) βA^2 45–52
58 YPFPGPIPN βA^2 60–68
60 APFPE(VF) αs1B 26–32b
aNumbering cf. Fig. 10.29.
bIn the literature, Q represents position 30 ofαs1-
casein B, and E the corresponding position of the pre-
cursor protein. () Added on the basis of the amino acid
composition.