The effects of serotonin, injected into one udder artery, on teat smooth muscle function were investigated in four lactating cows. Motility of longitudinal smooth muscles was recorded by a plethysmographic technique, and sphincter function by measuring milk leakage from the full udder. Serotonin (40, 120 and 360 μg) activated teat muscle tonicity and reduced the volume of milk leakage. The effects on longitudinal smooth muscles were reduced by mianserin and ketanserin (0·375, 1·5 and 6 mg) and by methysergide (1·5 mg). These blocking substances were also effective (0·2, 0·6 and 1·8 mg respectively) in antagonizing the inhibiting action of serotonin on milk leakage. It is suggested that serotonin effects are mediated by receptors of the S2-type.

Total bacterial counts of the milk from individual cows were measured for three groups of ten winter housed cows at three milkings. The teats were either (i) left unwashed or (ii) washed with disinfected water (60 ppm available iodine) and dried with individual paper towels or (iii) washed with plain water and then dried with a single fabric cloth impregnated with a polymeric bisguanide and a quaternary ammonium compound. The mean total bacterial counts/ml for the groups were 5820, 2108 and 1116 respectively. Treatments (ii) and (iii) were also compared for their ability to prevent the inter-teat transfer of bacteria. Before teat washing and drying, one teat of each cow was deliberately contaminated with Streptococcus agalactiae. Significantly fewer teats (5/30) became contaminated with Str. agalactiae when treatment (iii) was used for teat washing and drying compared with treatment (ii) (20/30).

Penetrability of the bovine teat duct to Escherichia coli endotoxin solution was measured before and after reaming the duct with a polypropylene tube, a steel twist drill bit, or a fluted drill point. There was some evidence of a transient increase in penetrability for one or two milkings following reaming but most ducts were not rendered penetrable to endotoxin. Histological examination of ducts after reaming showed that although the loosely packed superficial keratin was effectively removed a continuous smooth keratin layer remained covering the epithelium. These observations are discussed with respect to the possible mechanisms responsible for maintaining the defensive barrier of the duct to bacterial penetration.

The variation in plasmin activity and proteose-peptone (PP) content in milks from 81 cows of four breeds was statistically analysed. Plasmin activity increased with parity and stage of lactation and differed between breeds, but the breed effect was removed when adjustment was made for differences in milk casein content. The negative correlation found between plasmin activity and casein content seemed to be expressed only under assay conditions and was thus probably an artefact. The linear regressions of proteose-peptones in fresh (PP) and cold-stored milks (ΔPP) on plasmin activity were highly significant (P < 0·001). However, the variation in plasmin activity explained only 38 and 33%, respectively, of the variation in PP and ΔPP. At apparent zero plasmin activity, PP and ΔPP were significantly different from zero (P < 0·001) and the intercepts represented 77 and 46%, respectively, of the averages. PP and ΔPP were significantly higher in milks containing the BB genotype of ²-lactoglobulin than in milks with the AA genotype.

Six dairy cows were treated before milkings with either oxytocin (Pitocin, 20 i.u.) or ACTH (Synacthen, 150 i.u.), principally to determine their effect on the ratio of citrate:lactoferrin concentrations in the milk. With ACTH treatment, after 3 d milk yield and citrate concentration decreased significantly, lactoferrin and bovine serum albumin (BSA) concentrations increased significantly. Somatic cell counts (SCC) increased temporarily in the milk of three of the cows which previously had > 100000 cells/ml. Lactoferrin yield remained fairly constant but citrate yield was significantly reduced. The citrate: lactoferrin molar ratio decreased from 1373 to 606. With oxytocin treatment, after 4 d milk yield first increased and then significantly decreased, citrate concentration decreased significantly while there were no significant changes in lactoferrin or BSA concentration or in the yield of any other milk constituents. The citrate: lactoferrin molar ratio decreased from 1621 to 1301. There were no significant changes in SCC either during treatment or 4 d after treatment but there was a significant rise at 16 d after treatment. It was concluded that in lactating cows both hormones affected citrate and lactoferrin concentrations in the direction that would improve the antibacterial properties of milk, but that this was accompanied by adverse effects on milk secretion. The extent of the change was not sufficient to be likely to produce inhibition of coliform bacteria.

Enzymic digests of samples of heated skimmed milk were found to contain small amounts of S-carbamyl-L-cysteine. This material was concluded to have arisen from reaction of a cysteinyl residue in βlactoglobulin (β-lg) with cyanate derived from the native urea of bovine milk. After heating at 75 or 90 °C for 20 min skimmed milk contained 0·009 and 0·029 μmol/ml respectively of protein-bound S-carbamyl-cysteine. Evaporated milk contained 0·058 μmol/ml. The S-carbamylcysteine contents of samples of β-lg heated under similar conditions in equimolar 0·17 mM-KCNO at pH 6·6 were 0·016 and 0·062 μmol/ml respectively. At 60 °C no formation of S-carbamyl-cysteine was detected. Samples of evaporated milk and skimmed milk which had been heated for 20 min at 60, 75 or 90 °C were examined, after acid hydrolysis, for the presence of homocitrulline. None was found. Similarly αs1- and β-caseins heated at 60 and 75 °C in 4 mM-urea at pH 6·6 yielded no homocitrulline, but after treatment at 90 °C for 20 min αs1-casein contained 68 μg/g and β-casein contained 73 μg/g protein-bound homocitrulline. This was concluded to have been the product of reaction of cyanate and ε-amino groupings of lysyl residues of the caseins. The relative importance of carbamylation involving ε-amino groups or sulphydryl groups in milk is discussed.

The kinetics of the epimerization of lactose to lactulose were determined for two ‘model milk’ solutions, one containing lactose and the other lactose and lysine. The lysine was added to lactose to determine whether amino groups of proteins act as base catalysts promoting the production of free lactulose. The presence of lysine actually reduced the rate of production of free lactulose, presumably by the formation of amino-sugar complexes. The rate of production of free lactulose over the range of processing conditions was shown to be first order for both systems. Thermal effects on lactose were shown to be complex. The epimerization of lactose to lactulose was reversible and both sugars were thermally decomposed to their monosaccharides. The difference in the rate of production of free lactulose between the lactose, and the lactose and lysine solutions was also observed in processed milk and its ultrafiltrate (protein free).

The first stage in acid casein manufacture is the isoelectric precipitation of casein from skim milk. This stage controls the particle size of the casein curd which is important in the later washing, dewatering and drying stages. Casein was precipitated batchwise from 9% total solids skim milk using 0·3 M-H2SO4 at temperatures from 25 to 53 °C and at pH (measured in the whey) from 3·6 to 5·1. A wet sieving method has been developed for measuring the particle size distribution of the casein curd. Ferric ammonium sulphate was added to the curd/whey mixture to toughen the curd particles and to reduce their stickiness. For given precipitation conditions the particle size distribution could generally be modelled by a normal distribution. The mean particle size generally increased with increasing temperature and pH. The increase in particle size with pH was pronounced at 53 °C, while at 25 and 35 °C particle size varied little with pH. The calcium contents of washed casein curd samples were low at all precipitation pH at a precipitation temperature of 35 °C, but increased markedly above pH 4·4 at precipitation temperatures of 45 and 53 °C.

The effects of κ-casein and β-lactoglobulin (β-lg) genetic variants on cheesemaking were examined in two laboratory scale experiments. Variants of κ-casein had highly significant (P < 0·001) effects on milk citrate content (A > B) and rennet clotting time (A > B). When curds were cut at constant firmness there were only minor effects of κ-casein variants on milk component recoveries and cheese yield and composition. A tendency to higher fat recoveries from milks containing κ-casein B was reflected in significantly (P < 0·05) higher fat contents in cheese after 3·5 months of ripening. Genetic variants of βlg had highly significant (P < 0·001) effects on casein number (B > AB > A) and protein recoveries (B > AB > A) and significant (P < 0·05) effects on yield of cheese dry matter (B > AB > A). Green (unripened) cheeses made from the different milks also differed in fat, protein and moisture contents, probably in part due to differences in fat/casein ratios of the cheesemilks. The compositional differences were reflected in differences in the extent of proteolysis during ripening (A > AB > B). In the experiment with β-lg genetic variants the effect of time of cold storage of the cheesemilk was also investigated. No differences were found in milk composition and component recoveries or cheese yield, composition and quality when milks were cold-stored for 24, 48 or 120 h before cheesemaking.

The stability of lactase from Streptococcus thermophilus at 55 °C increased 7-fold, 2-fold and 1·5-fold in the presence of lactose, galactose and glucose respectively; maltose had no effect. Total stability over an 8 h period was more than 10-fold better in milk and sweet whey than in lactose solution, owing to the stabilizing influence of the milk proteins and the milk salts. Ovalbumin and reduced glutathione provided some extra stability but were not as effective as the milk components. In the absence of lactose the enzyme was less stable in milk and was not protected at all by sweet whey constituents. None of the milk protein fractions was as effective in the absence of lactose as when it was present. Enhanced thermostability of the enzyme in milk and sweet whey is due to contributions by all major milk components, but binding of lactose to the enzyme is the major factor controlling the extent of stabilization by other components.

Flavour, aroma and appearance of milks fermented with commercially available kefir grains were compared with similar characteristics of heat treated (90 ΰC/30 min) milks that had been fermented with aroma producing starters in addition to the kefir grains. The starters used were either a mixture of Streptococcus lactis subsp. diacetilactis and Leuconostoc cremoris (lactic culture) or of Str. thermophilus and Lactobacillus bulgaricus (yogurt culture).

Two methods of fermentation were investigated involving removal of the grains followed by (i) a second fermentation of the kefir with the aroma-producing organisms and (ii) combining the kefir with aroma-producing organisms for use as a starter to ferment a further sample of heat-treated milk. Products were assessed by a taste panel and marked for acceptability. Addition of lactic or yogurt cultures resulted in products with increased mean scores for aroma and more acceptable flavours.

Whey and deproteinated whey preparations with different carbon: nitrogen (C/N) ratios ranging from 7·5 to 73 were digested anaerobically in a downflow stationary fixed-bed reactor at 35 °C with a hydraulic retention time of 5 d. Effluent and biogas parameters indicated that no decrease in digestion and stability occurred at the highest C/N ratio. Chemical oxygen demand (COD) removal averaged 88%, while volatile fatty acids were maintained at a low level (< 500 mg l–1). Biogas yield averaged 0·423 m3 kg–1 COD and the methane content of the biogas varied between 57 and 63%. Ammonia toxicity occurred at a C/N ratio of 7/5 in the substrate feed. Virtually no ammonia N was detected in the effluent when whey substrates with C/N ratios of 50 and 73 were fed. Titration curves showed that buffer intensities in the effluent were not affected by a decrease in ammonia level. A decrease in the biomass content of the effluent which occurred as a result of the increase in C/N ratio of the substrate did not cause any rate limiting effect on biogas production. The removal of protein from the whey caused a reduction in the ratio of COD: total carbon in the whey. On average 59% of the carbon in the substrate was converted to biogas.