Dairy Chemistry And Biochemistry

416 DAIRY CHEMISTRY AND BIOCHEMISTRY

1

3000

AM2

GI IIC25

CJ^2000

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-z

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1000

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Aq Thr Ser Glu Pro Gly Ala Cys Val Met Ile Leu Tyr Phe His Lys Arg

Amino acid

Figure 10.24 Concentration of individual amino acids in 60-day-old Cheddar cheese, made
with a single-strain starter Lactococcus lactis ssp. cremoris AM,, Gll/C25 or HP (from
Wilkinson, 1992).

been isolated from the water-soluble fraction of Cheddar, and characterized
(Figure 10.23). These show that both lactococcal proteinase and exopep-
tidase contribute to proteolysis in cheese. The proteinases and peptidases of
the NSLAB (mainly mesophilic lactobacilli) appear to contribute little to
proteolysis in Cheddar, except in the production of amino acids.
The principal amino acids in Cheddar are shown in Figure 10.24.

10.2.8 Cheese Jla vow

Although interest in cheese flavour dates from the beginning of this century,
very little progress was made until the development of gas liquid chromato-
graphy (GC) in the late 1950s, and especially the coupling of GC and mass
spectrometry (MS). More than 200 volatile compounds have been identified
in cheese by GC-MS (principal compounds are listed in Table 10.7). The
volatile fraction of cheese may be obtained by taking a sample of headspace
but the concentration of many compounds is too low, even for modern
GC-MS techniques. The volatiles may be concentrated by solvent extrac-
tion or distillation. In the former, a large solvent peak may mask important
constituents while the latter may generate artefacts, even at moderately low
temperatures. Trapping of volatiles, e.g. on adsorbants or in cold traps, is
probably the most satisfactory method for concentration.
The taste of cheese is concentrated in the water-soluble fraction (peptides,
amino acids, organic acids, amines, NaCl) while the aroma is mainly in the
volatile fraction. Initially, it was believed that cheese flavour was due to one