Multiple regression analysis has been used to relate contributions of individual flavour components to the flavour of Cheddar cheese. Equations have been derived that relate Cheddar flavour to the headspace concentrations of 2-pentanone, methanethiol and methanol. The concentrations of ethanol and H2S found in cheese headspace have been related to the flavour defects ‘fruity’ and ‘sulphide’ respectively

Quantitative polyacrylamide gel electrophoresis has been used to measure residual native whey proteins remaining after heat treatment of skim-milk and cheese whey in a kinetic study. The denaturation of α-lactalbumin (α-la) appeared to be first order, but was probably a second-order reaction displaying pseudo first-order kinetics. The denaturation of both β-lactoglobulin A and B (β-lgA and β-lgB) followed second-order kinetics while that of serum albumin was more complex, and could equally well be described as first or second order. Equations are given relating log k1 (in s-1) to temperature for α-la denaturation in skim-milk between 70 and 95 °C and between 100 and 150 °C. Similarly, equations relating log k2 (in lg-1s-1) to temperature are given for ²-lgA in skim-milk between 100 and 150 °C, and for ²-lgB between 95 and 150 °C. The relative heat stability of ²-lgA and ²-lgB was found to vary.

Below 95 °C ²-lgA appeared slightly more thermostable than ²-lgB in skim-milk, and the same was observed in cheese whey below 100 °C. Above these temperatures ²-lgB appeared more stable than ²-lgA.

Denaturation of ²-lgB was only slightly more rapid in skim-milk than in whey at temperatures below 95 °C, but was significantly slower at higher temperatures.

It has been shown that there is a time-dependent transfer of β-casein and the milk serine proteinase system from micelles to milk serum with change of temperature from 38 to 4 °C. It has been established that the γ-caseins can be formed by proteolytic degradation of β-casein. By a simple extraction technique, the very hydrophobic γ-casein fraction was separated from stored milks (26 and 4 °C) and estimated quantitatively. The results showed that the proteolytic degradation of β-casein is faster at 4 °C than at room temperature and this can be explained by the immobilization of enzyme and substrate at the micelle surface at higher temperatures (26 °C).

The results indicate that irreversible changes during cooling for short periods do not cause problems in milk processing, but the formation of γ-caseins and phosphopeptides may influence the technological properties of raw milk stored for more than 48 h.

Measurements of residual native protein remaining after heat treatment of cheese whey have been made using quantitative polyacrylamide gel electrophoresis. The results have been expressed in terms of kinetic constants. The effect of concentration was investigated up to 3 times the normal total solids content, dialysis treatments were used to study the effect of non-protein constituents, and the effect of pH was studied at pH 4, 6 and 9. The results indicated that increased total solids (TS) concentration slowed the denaturation of β-lactoglobulin A and B (β-lg A, β-lg B) but hastened the denaturation of α-lactalbumin (α-la). However, increased lactose concentration slowed the denaturation of both α-la and β-lg, perhaps by preventing formation of heat-induced complexes. Increased Ca concentration, up to 0.4 mg/ml, tended to slow the denaturation of both proteins, but further increase in Ca up to 0.9 mg/;ml produced little effect. The rate of denaturation of both α-la and β-lg was slower at pH 4 than at pH 6 or 9, and was probably slowest at the isoelectric point. However, not all the changes associated with pH could be explained in terms of net molecular electrostatic charge. The genetic variants of ′β-lg showed different heat stabilities – below 90 °C β-lgA was more stable than β-lgB, but above 90 °C the situation was reversed at all TS concentrations, and pH 6. However, at pH 4 and 9, °-lgA was less stable than °-lgB over the entire temperature range at normal concentration.

The enzymic degradation of β-casein by immobilized trypsin is described and its use as a model system to study proteolytic reactions which occur in milk during processing is examined. Quantitative determination of proteolysis can be obtained by densitometric transmission measurement of patterns obtained by polyacrylamide-gel electrophoresis. Staining properties of some of the individual components in the electrophoretic patterns were determined by calibration with pure protein and peptide preparations. The isolation of pure β- and γ-caseins and the preparation of several forms of immobilized trypsin are outlined.

Possible mechanisms for the production of volatile sulphur compounds during the ripening of Cheddar cheese have been studied. Slurries of cheese made with and without starter organisms were treated with dithiothreitol (DTT) and the chemical composition of the headspace examined. Cheeses were also pressed from curd treated with DTT and glutathione (GSH). Reactions occurring between methionine, cystine and Na caseinate and reducing agents cysteine, DTT and GSH were also studied. In addition, the reactions of H2S with methionine and Na casein. ate were investigated.

Treatment of cheeses with DTT and GSH resulted in the production of H2S and methanethiol (CH3SH) together with the development of Cheddar flavour. Similar treatment of methionine and Na caseinate also yielded H2S and CH3SH whereas Cystine produced only H2S. H2S reacted with both Na caseinate and methionine to yield CH3SH.

These results are consistent with the occurrence of some of the chemical reactions studied during the ripening of Cheddar cheese.

The proteolytic activity in UHT-sterilized milk of a proteinase-containing fraction, prepared from the milk, is reported. The proteinase fraction was isolated from casein micelles as described by Reimerdes & Klostermeyer (1974).

The fraction was added to UHT milks and the proteolysis in the samples, measured as the liberation of non-protein nitrogen, compared with that in control samples without added proteinases. The increase in proteolytic activity and deterioration in samples containing added proteinases indicated that an enzyme process occurred in UHT-sterilized milk which could influence gel formation.

A method is described for the chromatographic analysis of the headspace of hard cheese. Among the cheeses examined were 12 commercial cheeses and 12 Cheddars made in the NIRD experimental dairy. The 12 commercial cheeses were Parmesan, Caerphilly, Stilton, Leicester, Double Gloucester, Cheshire, Gouda, Wensleydale and 4 varieties of Cheddar. It was found that those varieties containing low concentrations of sulphur compounds had little aroma and derived most of their flavour from taste and texture. The concentration of 2-pentanone was found to be a good indicator of maturity of Cheddar cheese.

Whey proteins have been isolated from cheese whey by complex formation with carboxymethylcellulose. The protein preparations form stable gels and foams when reconstituted in water. A study has been made of the effect of concentration, pH and temperature on the gelling behaviour of the whey protein isolates, and the conditions necessary for a standard gelling test have been defined. Proteose-peptones (p-p) have been prepared from a whey protein isolate which showed a strong tendency to gel, and also from heated and unheated milk. The gelling behaviour of whey protein isolates, which showed either no tendency or a strong tendency to gel, has been studied in the presence and absence of added p-p. The quantities added varied from 0·05 mg isolated from unheated milk to 15 mg from heated milk. No change in gelling time was observed, and it was concluded that p-p were not responsible for the gelling behaviour exhibited by whey protein isolates.

A method for the preparation of αs0-casein, and for the preparation of αs0-casein fractions 1 and 2 from buffalo casein are described. The amino acid composition and phosphorus content of αs0-casein are given and compared with those of other αs0-caseins.

In the past the classification of ATCC 7962 as a strain of Streptococcus lactis has been questioned because it contains β-galactosidase and not β-phosphogalactosidase, and because all extracts do not react with group N antiserum. A comparison was made between ATCC 7962 and known strains of Str. lactis using physiological properties, some of the properties of the lactate dehydrogenases and percent guanine plus cytosine in the DNA. ATCC 7962 was distinguished only by its ability to ferment pentoses. The degree of hydribization between the DNA of ATCC 7962 and that of a typical strain of Str. lactis was 67 %. ATCC 7962 is an atypical strain of Str. lactis. The properties of a wild strain of Str. lactis isolated from radishes in Brunei which contains β-galactosidase and β-phosphogalactosidase, are given also. This strain ferments pentoses.

Human β-casein occurs in multiphosphorylated forms having the same amino acid composition but with 0–5 phosphate groups/molecule. Sequence analysis was used to determine whether each of the phosphorylated forms is a mixture of species having a certain number of phosphate groups randomly distributed or whether each form contains phosphate groups on specific seryl or threonyl residues. It was found that forms containing 2, 4 and 5 phosphate groups/molecule are homogeneous with respect to their phosphorylation sites. The monophosphorylated form, however, is a mixture of equal amounts of species phosphorylated at residues 9 or 10.