Changes in mammary blood flow, arterial and venous plasma concentrations of glucose and individual amino acids, udder volume, and milk yield and composition were measured at intervals throughout lactation in four Friesland ewes. Milk yields peaked 50–80 d post partum and declined by 40% within 3 months. Neither mammary blood flow (43·3 ± 5·8 (s.e.m.) ml/100 cm3, min) nor udder volume changed significantly throughout the period of study, but for three ewes the ‘mammary blood flow:milk yield’ ratio increased from 300 (peak yield) to 570 (late lactation). Mammary glucose uptake remained essentially constant throughout lactation despite a 50% decline in lactose output. Arterial concentrations of glucose were much lower at peak yield than in late lactation. Mammary amino acid uptake conformed quite closely to ‘essential’ and ‘non essential’ categories previously defined for goats and cows, the degree of balance with output in milk protein being similar at all stages of lactation. For several amino acids arterial concentrations and arteriovenous differences were significantly positively correlated: the changes in arterial concentrations with lactation stage were also correlated for some amino acids. Apart from the intrinsic value of such studies on a breed of ewe increasingly used for dairy purposes, the Friesland ewe appears well suited for use in quantitative metabolic studies on lactation.

A method is described for preparing immunologically homogeneous human milk β-casein, against which monospecific rabbit antiserum was prepared. The antiserum was used to quantify β-casein, the major human casein, by rocket Immunoelectrophoresis in individual milk samples. However, it was found that in most samples β-casein occurred together with degradation products originating from its proteolysis by plasmin. Immunological quantification of human β-casein, treated with plasmin for various time periods, showed that rocket height was not affected by proteolysis up to degradation states clearly more advanced than those observed in all samples of fresh human milk tested. Assays of 150 individual milk samples from 80 women, covering a lactation period of up to 730 d, gave an average concentration of β-casein (native+degraded) of 4·67±0·89 standard deviation (g/1); extremes at 2·1 and 7·3 g/1 did not vary significantly during the period under study. Comparison of this average value with an accepted casein content of 4·4 g/1 (Macy & Kelly, 1961) showed that the casein content of human milk is underestimated when obtained by N determinations on milk and on its supernatants at pH 4·6 (whey). Caseins other than β-casein occurred only in minute amounts, if at all.

Although β-lactoglobulin (β-lg) has been considered to be absent from human milk, recent results of other workers, based on immunological reactions between human milk and rabbit antiserum to bovine β-lg, suggest that this protein may be present. Although our results show similar immunological reactions, we consider that lactoferrin is responsible for these, as it was the only reactive protein species which could be prepared to homogeneity. Indeed two types of antibodies were found by ELISA test in the antisera to bovine β-lg. One of them would be able to bind loosely to human lactoferrin, but its binding sites would not be antigenic in the rabbit.

The effect of separating conditions on lipase activity and free fatty acid levels in preheated milk, cream and skim milk was measured on nine occasions during a 12-week period covering the seasonal change from winter feeding to summertime grazing. This change consisted of four periods each representing a different type of forage intake, namely: silage, kale, daytime grazing and 24 h grazing. Milk was separated at 30, 40, 50 and 60°C with preheating times of 10, 25 and 55 s. Results were expressed both as absolute values and in terms of changes relative to the original unheated milk. Lipase activity and free fatty acid concentration were significantly reduced as separation temperature increased but were not influenced by holding time. The loss of activity in cream was progressive so that at 60°C only 40% of the original activity remained. Up to 50°C little change occurred in preheated milk or skim milk activity, while at 60°C 83 and 76% respectively of the original activity remained. The amount of activity calculated to be associated with the fat fraction of the cream also decreased with temperature. Activity varied significantly with date; maximum values were observed during the first 3 weeks of summertime grazing. Relative activity values indicated that the susceptibility of milk lipase to heat inactivation also varied with date. Lipolysis was also significantly affected by date. Cream free fatty acid levels were lower during the period of daytime grazing and were significantly higher than those in preheated milk. The correlation between lipase activity and free fatty acid levels was generally poor, accounting for between 0 and 34% of the variance. Possible reasons for the effect of separating temperature on lipolysis in cream are discussed.

Extended X-ray absorption fine structure spectra, above the Ca K absorption edge, were recorded from lyophilized casein micelles obtained from the milk of cow, pig, goat, rabbit and rat. A spectrum was also obtained from the calcium phosphate prepared from the casein micelles of human milk. Comparison of these spectra showed that the short-range environment of calcium in the micellar calcium phosphate was the same in all six species. Furthermore, these spectra closely resembled that of brushite (CaHP04. 2H20). However, X-ray diffraction showed no evidence for an extensive crystal lattice in micellar calcium phosphate.

Time/temperature profiles were obtained for commercial ultra high temperature (UHT) and sterilized milk processing plants and for a pilot UHT plant operating under nine different conditions. Samples of milk from each process were analysed for lactulose by an enzymic method, yielding concentrations of lactulose of 4 to 118 mg/100 ml. The measured lactulose concentration could be derived from the corresponding time/temperature profile by assuming an Arrhenius relationship with an activation energy of 152 kJ mol-1, for the whole range of UHT and in-container processes examined.

The cheesemaking properties of recombinant chymosin from Escherichia coli were compared with those of standard rennet in parallel trials with three single strain starters. For each pair of cheeses the cheesemaking characteristics, recoveries of milk solids in the curds and compositions were similar. The rates and types of proteolysis and texture development during ripening between cheeses made with the two coagulants were not significantly different.

The inhibitory effect of five disinfectants on acid production by Streptococcus lactis and Str. cremoris Cheddar cheese starters was compared using two techniques, a laboratory scale fermentation tube test, and pilot scale cheese manufacture. Threshold inhibition concentrations (partial, total) of disinfectants (mg/1) on acid production observed in the fermentation tube were: peracetic acid/H2O2 (0–5, > 600) iodophor (75–220, > 400), quaternary ammonium compound (QAC), (20–30, > 200), acidic anionic (60–120, 600–1200), and Na hypochlorite (400–1000, > 1000). Threshold inhibition concentrations (partial, total) observed in the cheese vat were (mg/I); peracetic acid/H2O2 (0–5, 5–35), iodophor (15–30, 75–200), QAC (10–20, > 200), acidicanionic(30–120, > 600), and Na hypochlorite (35–400, > 400). Flavour threshold concentrations in the cheese at 4 weeks were (mg/l): peracetic acid/H2O2 5, iodophor 8, QAC 20, acidic anionic 12, and hypochlorite 50. It is concluded that problems in cheese manufacture are unlikely to occur with hypochlorites, iodophors, and acidic anionics, but that care should be taken when using QAC and peracetic acid as sanitizers. A correlation coefficient of 0918 was computed between the two methods of determining partial acid inhibition (P < 0·005).