The maturation of cheese

Glycerides

Fatty Acids -► Hydroxy fatty acids

Fatty Acids -► Hydroxy fatty acids

Ethyl esters

Alkan-2-ones

Thioesters

Ethyl esters

Alkan-2-ones

Alkan-2-ols

Fig. 10.3 Reactions of lipids involved in the development of cheese flavour.

Deaminases Acids

Carbonyls

Casein

Proteinase Polypeptides

Proteinase

Peptides

Peptidase

Amino acids transaminases Deçarbo-^^Lyases xylaÈes

Keto acids

Amines

Sulphur compounds

Fig. 10.4 Reactions of proteins involved in the development of cheese flavour.

Table 10.4 Examples of flavour-active volatiles in cheese and their origins.

Substance

Origin

Route

3-Methylpropionic acid

Leucine

Deamination

2-Keto-4-methylpentanoic acid

Leucine

Transamination

3-Methylbutanal

Leucine

Decarboxylation of 2-keto-4-methylpentanoic acid

4-Methylpentanoic acid

Leucine

Deamination

3-Methylbutanal

Leucine

Reduction of 3-methylbutanal

3-Methylbutanoic acid

Leucine

Oxidation of 3-methylbutanal

4-Methylthio-2-ketobutyrate

Methionine

Transamination

Methional

Methionine

Decarboxylation of 4-methylthio-2-ketobutyrate

2-Keto-4-thiomethylbutyrate

Methionine

Deamination or transamination

Methanethiol

Methionine

Demethiolation of 2-keto-4-thiomethylbutyrate

Dimethyl disulphide

Methionine

Degradation of methanethiol

Dimethyl sulphide

Methionine

Degradation of methanethiol

Hydrogen sulphide

Methionine

Degradation of methanethiol

Dimethyl trisulphide

Methionine

Addition of sulphur to dimethyl disulphide

Methyl thioacetate

Methionine

Reaction of methanethiol with acetyl-CoA

Tyramine

Tyrosine

Decarboxylation

^-Hydroxyphenylpyruvate

Tyrosine

Transamination

^-Cresol

Tyrosine

Via ^-Hydroxyphenylpyruvate

Indolepyruvate

Tryptophan

Transamination

Skatole

Tryptophan

Via Indolepyruvate

2-Methyl butanal

Isoleucine

Strecker degradation

proteolytic enzymes, including aminopeptidases, may be important for the growth of organisms that function in maturation. Figures 10.3 and 10.4 illustrate some of the biochemical pathways that can occur during maturation of cheeses. Table 10.4 lists a range of flavour-active substances in cheese derived from these and other reactions. This is a very restrictive list and is meant to be merely illustrative of the way in which the wide diversity of flavour-active species arise.

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