A new method for monitoring the terminal stages of proteolysis in cheese, i.e. the formation of free amino acids, using the Cd-ninhydrin reagent is reported. The assay was very specific for free amino acids and may be performed on citrate-soluble, water-soluble or phosphotungstic acid-soluble fractions of cheese, but not on trichloroacetic acid-soluble extracts; water-soluble extracts were chosen for routine analysis. Application of the assay to several experimental cheeses showed almost linear increases in free amino acids during ripening for up to 12 months with a slightly faster rate of formation during the later stages of ripening.

Penicillium caseicolum has been shown to completely synthesize styrene. A medium was developed to test the capacity of different strains for this synthesis. In a synthetic medium, styrene production began only after the glucose was entirely consumed. This production depended on storage temperature and occurred simultaneously with 1-octene-3-ol formation.

The transport of K+ (Rb+) and Cl− by membrane vesicles isolated from bovine milk has been studied using ion-exchange column chromatography. K+ (Rb+) and Cl− accumulation by the vesicles was time-dependent and was almost abolished by 0·1% Triton X-100, suggesting that uptake represents ‘real’ transport rather than binding. K+ (Rb+) uptake was influenced by the anion in solution in a manner suggesting that influx is sensitive to changes in vesicle membrane potential. Similarly, Cl− uptake was found to be sensitive to vesicle electrical potential: Cl− influx was enhanced by inside positive potentials. Cl− uptake was not saturable with respect to external Cl−. The results suggest that K+ (Rb+) and Cl− cross the apical membrane by way of conductance pathways. The similarity between ion transport by skim milk membrane vesicles and that of the apical aspect of the intact mammary epithelium suggests that the former may be a good model to study solute transport by the apical membrane of mammary secretory cells.

Part of the milk used for manufacturing Domiati cheese was replaced by buttermilk at rates of 0, 20, 30, 40, 50 and 60%. The fat and SNF contents were standardized at 5 and 10% respectively. The hypocholesterolaemic effect of buttermilk when incorporated into cheese was tested with rats by including cheese manufactured with and without buttermilk mixed in their diet at a rate of 30% for a period of 60 d. When the diet containing Domiati cheese free from buttermilk (control cheese) was given to rats, there were highly significant increases in serum and liver cholesterol. However, when part of the milk used in manufacturing Domiati cheese was replaced by buttermilk the increases in serum and liver cholesterol concentrations were reduced. These reductions were proportional to the proportion of buttermilk incorporated in the milk used to manufacture the cheese. When 50% of the milk used for Domiati cheese was replaced by buttermilk the hypercholesterol-aemic effect of Domiati cheese was nullified and the serum and liver cholesterol concentrations were restored to their normal values. The effect of replacing 50% of the milk used in the manufacture of Domiati cheese by buttermilk on the quality of the cheese was tested periodically during the ripening period. The buttermilk improved the flavour of the cheese whilst only slightly affecting its ripening.

The inhibitory effects of cultured milk using 76 strains of lactic acid bacteria isolated from milk products were investigated on the mutagenicity of 3-amino-1-methyl-5H-pyrido[4,3−b]indole (Trp-P2), a tryptophan pyrolysate for Salmonella typhimurium TA98. Each cultured milk sample displayed its characteristic antimutagenic effect against the mutagenicity of Trp-P2. The milk cultured with Lactobacillus acidophilus LA106 (LA2) showed the highest inhibition of 82·1% among the strains used. Milk samples cultured with Lactococcus lactis subsp. lactis, L11103 (10−3) and L11102 (KM) also exhibited higher inhibition percentages.

Streptococcus salivarius subsp. thermophilus strain NST5 exhibited a temperature-dependent defence mechanism against the virulent bacteriophages φ.B1.2 and φA1.1. It was active at 42 °C but not at 30 °C as demonstrated by a significant increase of both plaque size and efficiency of plaquing. This defence mechanism did not affect host-dependent phage replication and did not interfere with phage adsorption to NST5. These results suggest that it interfered with phage development. The phages φT33, φT58, φD1, φT21 and φT9, belonging to the same phage type as φB1.2, were examined for their ability to infect NST3 and NST5. Restriction modification systems of different specificity were detected in NST3 and NST5; host-dependent phage replication was detected at 30 and 42 °C; an abortive defence mechanism was detected in NST5 which was active at 42 °C, but not 30 °C, and was independent of restriction modification action or interference with phage adsorption. Our investigations of phage-host interactions showed that the two Str. salivarius subsp. thermophilus strains studied avoided attack by related bacteriophages by evolving at least three different resistance systems.

The kinetics of lactate dehydrogenase from Leuconostoc lactis NCW1 were studied. The pH optimum for the enzyme depended on the concentration of pyruvate used in the assay and the enzyme displayed an ordered mechanism with respect to substrate binding. The Km for pyruvate and NADH and the Vmax of the enzyme decreased 20–, 30– and 6-fold respectively as the pH decreased from 8·0 to 5·0. No activators were found and none of the intermediates of the phosphoketolase pathway tested inhibited the enzyme. ATP, ADP, GTP and NAD+ were inhibitory. The intracellular volume (Volin) and intracellular pH (pHin) decreased as the extracellular pH (pHex) decreased. Co-metabolism of citrate and glucose affected the Volin but did not affect the pHin, which decreased by 0·6 units per unit change in pHex; at pH 7·0, the pHin and pHex were equal. The results suggest that pHin may play a role in determining the production of diacetyl and acetoin at low pH by Leuconostoc.

Bovine colostrum was investigated as a source of biologically active molecules capable of stimulating the growth of mammalian cells in culture and modifying the immune response in a murine model. An extract prepared from bovine colostral whey by cation exchange and re versed-phase chromatography stimulated the growth of L6 rat myoblasts, Balb/c-3T3 mouse fibroblasts and BHK-21 baby hamster kidney cells with equal or greater potency than fetal bovine serum. Fractionation of the bovine colostral extract by gel-permeation chromatography in M-acetic acid identified a number of cell-growth factors for each cell type. Bovine colostral extract was compared with an ovine colostral whey preparation for its ability to modulate IgE antibody responses in mice. Doses of 8 and 4 mg/d of ovine colostral whey or bovine colostral extract specifically suppressed IgE antibody responses, whereas at lower doses suppression did not occur. We conclude that bovine colostrum contains cell-growth factors as well as immunomodulatory factors that are able to regulate the IgE response in a heterologous species.

Psychrotrophic bacteria isolated from raw milk were tested for their ability to adhere to steel, two types of rubber, and glass, materials employed in the construction of milking equipment. The adherence assays were carried out by exposure of the materials to radioactively labelled bacteria in both a buffering solution (Ringer's) and milk. The degree of adherence of Gram-positive bacteria was lower (P < 0·001) than that of Gram-negative bacteria. Glass was the material least prone to bacterial adherence (P < 0·001); there were no significant differences between the other three materials. Milk was found to inhibit adhesion significantly (P < 0·05), this inhibition being more evident with the most adherent bacteria. There was no statistically significant correlation between bacterial surface hydrophobicity and adherence. Our results suggest that intrinsic bacterial adherence cannot be considered a relevant factor in the contamination of milking equipment.