Guinea pig mammary glands which were either lactating, involuting or dry were infused with colloidal carbon or killed staphylococci. At different time intervals following infusion, animals were killed and the superficial inguinal lymph nodes examined for the presence of carbon. Sides which had nodes with visible carbon were designated ‘positive’. The time intervals from infusion to positive for the three groups were compared using logistic regression. The times required for 50 % of the sides to be positive were estimated to be ˜4 h for lactating glands, 32 h for those in involution, and 13 min for dry glands. Histological differences in distribution of carbon in the mammary tissue suggest that differences in transit time may have been due to different mechanisms of transport through the glands in the three different physiological states. The distribution of bacteria was similar to that of the carbon in the corresponding tissues.

The activities of glucose 6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, isocitrate dehydrogenase, malic enzyme, lactate dehydrogenase and malate dehydrogenase have been determined in secreted milk from sows, rats and rabbits. Within each species, although there was considerable variation in the absolute activities of these enzymes, the relative activities were similar to those observed for, or previously published for mammary homogenates. The only exception was milk glucose 6-phosphate dehydrogenase which tended to lose activity upon prolonged storage in the mammary gland. These results suggest that the pattern of milk enzymes can be an accurate reflection of that occurring in the mammary gland.

Fibronectins were isolated from both bovine colostrum and fresh milk, and they were found to be very similar to plasma fibronectin. The concentration of fibronectin in milk decreased post partum: 30 µg/ml after 0 d and 2 µg/ml after 7–851 d. No fibronectin could be detected in any brands of ultra heat treated liquid milk on the market (≤0·006 µg/ml).

The lactoperoxidase/SCN-/H2O2 system (LPS) was found to inhibit lipoprotein lipase (LPL) in milk. Inhibition was related to the amount of SCN-/H2O2 added to milk. Lipolysis was unaltered until LPL activity was decreased to <40% of the original activity. When LPL was inhibited further, decreased lipolysis was observed. Purified LPL was also inhibited by LPS, at similar concentrations of SCN-/H2O2 as in milk. It was shown that non enzymically prepared OSCN- inhibited LPL at concentrations comparable to those produced by the LPS. Cysteine could eliminate the effect of LPS on LPL. The sulphydryl reagents dithiobisnitrobenzoic acid and Na tetrathionate had no effect on LPL activity.

A study of the content of water soluble vitamins in the 12 baby milk formulae available in the UK in April 1983 showed that levels of vitamins in the individual brands were generally in excess of those declared by the manufacturer. For cows' milk based formulae the mean excess of vitamins over the declared level was 94%. Vitamin levels in prepared formulae averaged three times the minimum recommended level. The average level of B vitamins in prepared cows' milk based formulae was six times higher than in mature human milk. For the two soya based products, the levels of vitamins were generally in excess of the declared level and levels of vitamin B12, biotin and, in one sample, vitamin B6 were considerably in excess of those found in mature human milk.

Preheating milk at 140 °C for 1 min at pH 6·6, 6·8, 7·0 or 7·2 shifted the heat coagulation time (HCT)/pH profile to acidic values without significantly affecting the maximum stability. Whey proteins (both β-lactoglobulin and α-lactalbumin) co-sedimented with the casein micelles after heating milk at pH < 6·9 and the whey protein-coated micelles, dispersed in milk ultrafiltrate, showed characteristic maxima–minima in their HCT/pH profile. Heating milk at higher pH values (> 6·9) resulted in the dissociation of whey proteins and κ-casein-rich protein from the micelles and the residual micelles were unstable, without a maximum–minimum in the HCT/pH profile. Preformed whey protein–casein micelle complexes formed by preheating (140 °C for 1 min) milk at pH 6·7 dissociated from the micelles on reheating (140 °C for 1 min) at pH > 6·9. The dissociation of micellar-κ-casein, perhaps complexed with whey proteins, may reduce the micellar zeta potential at pH ≃ 6·9 sufficiently to cause a minimum in the HCT/pH profile of milk.

A set of 12 fractions was isolated from homogenized cows' milk by a method of successive centrifugation steps. The fractions were analysed in terms of fat and protein contents and the diameters of the particles in them were also measured. Detailed comparisons of the turbidities of the samples and their light scattering properties allows comparison between them. It is concluded that the separation is less effective than a similar technique applied to casein micelles, but nonetheless that the different fractions do contain particles with different properties.

Bovine milk cream (40% fat) was ripened under different time/temperature/inoculum conditions with Streptococcus lactis subsp. diacetilactis DRC-1 before converting by heat treatment into ghee (Indian clarified butterfat). Biochemical changes in cream, in terms of titratable acidity, volatile acids, diacetyl and acetaldehyde and flavour changes in the ghee made from it in terms of free fatty acids (FFA), total carbonyls (TC) and flavour score, were studied. Of the different combinations of ripening conditions, 30 °C, 18 hand 3% inoculum produced optimum changes in the cream which resulted in the development of the most desirable flavour in the ghee, being comparable to that of desi ghee (made by the indigenous method). The flavour characteristics as determined by FFA (% oleic acid), TC (μmol/g fat) and flavour score (out of 10) of the best ripened cream ghee were found to be 0·54, 6·756 and 8·83 respectively. The flavour of ghee became impaired after a particular level of acidity developed in cream after 18 h incubation. The optimum conditions of ripening standardized under laboratory conditions were also extended to a semi-industrial scale.

Cheddar cheeses were made from milks concentrated 3- to 6-fold by ultrafiltration. Modifications to the conventional cheesemaking process were designed to obtain the correct composition and pH value in the final curd, improve the fat and moisture retention and cheese texture, and increase the ripening rate. The compositions of all cheeses were similar to those of controls made with unconcentrated pasteurized milk. The curd and cheese structures and the textural properties of the cheeses were closer to those of the controls when made from milk concentrated 5-fold than when made from milk concentrated 3-fold. Light homogenization of the milk before concentration led to improved fat recovery and decreased graininess and crumbliness in the cheese. Lowering the coagulation temperature of concentrated milks gave improved curd structure and less grainy and more sticky cheeses. Addition of the bacterial proteinase, Neutrase, with the salt, stimulated proteolysis and flavour production in the cheeses and made them more sticky. Neither reduction of the mineral levels in the milk by acidification before concentration nor reduction of the lactose concentration by diafiltration had any significant effect on the composition or textural properties of the cheeses.

The effect of storing Cheddar cheeses at elevated temperatures on proteolysis and flavour development was examined. Cheeses were stored under the following ripening conditions: (1) 8 °C for 32 weeks (control); (2) 15 °C for 8 weeks then 8 °C for 24 weeks; (3) 17·5 °C for 8 weeks then 8 °C for 24 weeks; (4) 20 °C for 8 weeks then 8 °C for 24 weeks; (5) 15 °C for 32 weeks; (6) 17·5 °C for 32 weeks; and (7) 20 °C for 32 weeks. The rates of build up of products of proteolysis and flavour increased in the order of the above treatments and substantial acceleration of ripening was achieved. However, after 32 weeks at 17·5 °C and 16 weeks at 20 °C, cheeses received significantly lower preference scores than the control cheeses (P < 0·05) mainly owing to the development of off flavours. The maximum temperature at which cheeses could be stored for 32 weeks without reduction in quality was 15 °C. Cheeses stored at this temperature for the entire period had levels of products of proteolysis at 12 weeks of age which were similar to those of controls at 32 weeks, and estimations of age at 20 weeks which were similar to those of controls at 32 weeks.

The composition of the diet fed to cows, the composition and coagulating properties of the milk produced by them and used for cheesemaking, the cheesemaking methods and the chemical composition, texture and grade of Cheshire cheese obtained from four farmhouse producers during the period December to June 1982–83 were investigated. The presence of pockets of loose fat in the cheese structure, which can lead to downgrading in the late winter and spring, was not related to the chemical composition of the milk and may arise from the handling of the milk before cheesemaking. Generally the composition of the forage and the milk varied with date, but not between the different farms, whereas the composition and properties of the cheese were dependent on the manufacturers but were fairly constant during the period of study.

Interrelationships between concentrations of constituents of forages in diets fed to the cows, milks and cheeses, rennet coagulation properties of milks, manufacturing methods and the grades and textural properties of the cheeses produced by four farmhouse producers of Cheshire cheese were studied during the period December 1982 to June 1983. Many intercorrelations occurred in concentrations of constituents of the milks and ultrafiltrates. Rennet coagulation properties were related to concentrations of many of the constituents of the milks and forages in the diet. Many interrelationships in parameters of cheese texture and components of cheese composition were observed. Compositions and texture of the final cheeses were generally not related to the composition of the milks used in their manufacture.