The fatty acid content of triacylglycerols (TG) in arterial and mammary venous blood plasma has been analysed in five cows that were close to peak lactation. The fatty acids in arterial TG were extracted by the mammary gland in amounts 14:0 < 16:0 < 18:0and 18:0 > 18:1n – 9 > 18:2. The difference of extraction between palmitate and stearate was similar in different TG species. The fatty acid 18:1n – 7, which was largely the trans isomer, was extracted more than 18:1n – 9. Significant amounts of phytanic acid were acylated in plasma TG, but not extracted by the mammary gland.

C-reactive protein (CRP) and serum amyloid P component (SAP), which are known to increase in sera from humans and many other animals with acute inflammation caused by infection, toxic drug administration or injury, were previously purified from bovine serum. These serum levels were determined by enzyme-linked immunosorbent assay (ELISA) using specific antiserum to bovine CRP or SAP which was prepared by immunizing rabbits and goats with each purified protein. Among 68 healthy Holstein cows, 45 non-lactating cows had levels of CRP and SAP of 20·6±1·4 and 27·6 ± 1·3 μg/ml respectively; 23 lactating cows had higher levels of CRP and SAP (76·0±13·6 and 38·3±5·5 μg/ml respectively). In the latter group, there was a high correlation between milk yield and serum CRP levels (P <0·001). From these observations, it was assumed that lactation might stimulate CRP synthesis rather than SAP synthesis in bovine liver as an acute phase reaction, and that CRP might be called a lactation-associated protein.

In a series of short-term experiments cows were subjected to exaggerated bacterial challenge and accentuated milking machine conditions known to predispose to new mammary infection. The incidence of new intramammary infection was significantly greater in quarters with peak flow rates > 1·6 kg/min whether they were exposed to impacts (P < 0·05) or milking without pulsation (P <0·001). The infection rates were much lower (P < 0·001) in quarters milked with ‘pulsation and shields’ to protect against these two machine factors. Despite this, quarters with peak flow > 1·6 kg/min still showed a 12-fold increase in mastitis incidence compared with quarters with peak flow < 0·8 kg/min. Rates of milk flow have increased dramatically in the last 40 years through selection and breeding: whole udder peak flow rates in heifers have doubled from 1·9 to 3·8 kg/min. Increased emphasis, therefore, should be placed on hygiene, husbandry and milking techniques to minimize bacterial numbers at teat ends to control mastitis as the drive for higher flow rate and yield make cows increasingly more susceptible to infection. These results suggest that the benefits of reduced infection rate from mastitis control are significantly underestimated since animals are now considerably more susceptible than 40 years ago.

The effect of preheat treatment, evaporation and drying in a commercial plant on the denaturation of βlactoglobulin and α-lactalbumin, their incorporation into the casein micelle and the heat stability characteristics of the milks and powders were determined. Preheat treatments between 110 °C for 2 min and 120 °C for 3 min denatured between 80 and 91% of β-lactoglobulin and between 33 and 45% of α-lactalbumin. Evaporation increased the extent of denaturation but spray drying did not increase it further. The incorporation of α-lactalbumin and βlactoglobulin into the micelles was markedly less than the amount that denatured and was not a constant ratio to it. Heat coagulation times at 140 °C of milks, concentrates and powders diluted to the original milk concentration were measured as a function of pH. In general, the greater the collective heat treatment, the shorter the time required to achieve coagulation. Spray drying shifted the peak positions in the pH-heat coagulation time profiles. In contrast, heat coagulation times (measured at 120 °C) of concentrates and powders diluted to 20% total solids content increased with the severity of the preheat treatment. Surprisingly, spray drying markedly increased the heat coagulation times of the diluted concentrates.

β-Casein amino groups were modified with aldehydes and dialdehydes via reductive alkylation at pH 8·0. The degree of alkylation was controlled by the amount of the alkylating reagent applied. The initial rates of α-chymotrypsin-catalysed hydrolysis of alkylated β-casein were inversely related to the size of the modifying group. Proteolysis of modified β-casein with trypsin (18 h) or with α-chymotrypsin (48 h) depended on the nature and size of the substituent applied. The measurements of tryptophan fluorescence indicate that the modifications also induced conformation change. Solubilities of methyl-, ethyl- or benzyl-β-casein slightly increased; solubilities of β-casein dialdehyde derivatives were significantly lower than that of native β-casein. Emulsion stability of methyl- or ethyl- β-casein was higher than that of native β-casein in the acidic pH range. After modification with glyoxal, the emulsifying activity and the emulsion stability of β-casein decreased. The emulsifying activity of benzyl- β-casein was lower than that of native β-casein. Phthalylated β-casein displayed the poorest emulsion stability.

The conversion of the two-dimensional size distribution of casein micelles, observed by electron microscopy in a plane section, to the three dimensional distribution is discussed and the average size parameters evaluated by several methods are compared. It is shown that parameters containing the −1 moment of the two-dimensional distribution, i.e. Dn, the number of micelles per unit volume and the width of the size distribution, are sometimes uncertain. The occurrence of negative numbers in some of the classes of the distribution is discussed and remedies are suggested. Sections were made by freeze-fracturing skim milk samples; the pH of the milk was between 5·5 and 6·7.

The antioxidant activity of casein and Maillard reaction products obtained by reaction of casein with glucose or lactose was studied. Antioxidant activity was evaluated in a model System containing methyl linoleate with haemoglobin as a pro-oxidant. Casein was antioxidative and heating casein in the presence of glucose or lactose resulted in enhancement of antioxidant activity. The development of antioxidant activity in reacted casein–sugar mixtures was determined as a function of initial casein and sugar concentration. The observed antioxidant activity of reacted casein–sugar mixtures was due to casein itself and Maillard reaction products resulting from reacting casein with sugar.

Cation-exchange chromatography on a Mono S column (Pharmacia) was used to separate macropeptide from whey proteins. Macropeptide was eluted by 0·1 M-NaCl in a 20 mM-KCl–HCl buffer, pH 2. This technique was suitable for quantitative determination of macropeptide in rennet whey and also for following the action of chymosin on κ-casein in skim milk. Precipitation at pH 4·6 was used to remove residual caseins and to keep macropeptide in solution. In comparison with other methods for determining macropeptide, the present one eliminates the need for pretreatment of samples with trichloroacetic acid (TCA) and allows the recovery of all the macropeptide. Quantitative determination of macropeptide in the 8% TCA-soluble fraction by cation-exchange chromatography showed that only 50–75% of the macropeptide was recovered. This chromatographic technique could also be applied for isolating and producing whole macropeptide on a preparative scale.

Moisture sorption isotherms of khoa were determined at 15, 25, 35 and 45 °C over a water activity (aw) range of O·l 1–0·97. The isotherms were sigmoid (Type II) and were fitted to the Guggenheim–Anderson–de Boer (GAB) equation (Bizot, 1983). The aw of freshly made khoa was found to be 0·96. The aw of khoa increased with increasing temperature up to 0·9; above this the effect of temperature on aw diminished. The monolayer moisture content of khoa decreased with increasing temperature. The equations describing the temperature dependence of GAB constants were determined in the form of the Clausius–Clapeyron equation. The net isosteric heat of desorption of khoa decreased rapidly until a moisture level of 0·1 g/g solids, and approached a constant value of 0·43 kJ/mol above a moisture level of 0·25 g/g solids.

This work aimed to relate changes in rheological behaviour with structural details of different sweetened condensed milk samples as well as to clarify the role of additives in delaying gelation. To study the process of gelation, rheological techniques were applied to fresh and stored condensed milk samples for times and at temperatures known to favour gelation (45 d at 37 °C). Electron microscopy techniques were used to relate the rheological changes with observed structural details. Examination by electron microscopy showed that micellar aggregation and association of casein micelles with fat globules increased during storage. The whey proteins appeared to play an important role in the thickening process.

The speed and duration of cutting the coagulum were varied during the commercial manufacture of Cheddar cheese in nine Damrow cheese vats on each of 3 consecutive days. The effects of the variations were assessed by determining the curd particle size distribution and fat and fines losses into the whey at draining. Short durations of cutting at slow speeds produced small curd particles and high fat losses into the whey. As the duration and/or speed of cutting was increased, average curd particle size increased while fat losses into the whey decreased. A maximum particle size and minimum fat level were reached after the Damrow's knife panels had completed approximately 37 revolutions. Further increases in speed and/or duration of cutting decreased curd particle size. Fat losses did not increase significantly. The hypothesis suggested to explain the results of these trials is that curd particle size is determined not by the cutting programme alone, but by a combination of the speed and duration of cutting and the subsequent speed of stirring prior to cooking. Fat losses in the whey are also influenced by this combination. Based on this hypothesis, a model is proposed which explains how variation in cutting speed and duration, followed by a constant stirring speed, determines curd particle size distribution in a Damrow cheese vat. Implications of the present findings in relation to cheese yield (losses of fat and fines into the whey) are discussed.

The influence of lactic starter inoculation on La Serena cheese characteristics was investigated in duplicate experiments, each consisting of a vat inoculated with 1% Lactococcus lactis subsp. lactis skim milk culture and a control vat without lactic starter. Lc. lactis inoculation achieved a significant pH decrease in the interior and on the surface of cheese, which ranged from 0·09 to 0·25 units throughout ripening. Breakdown of αs1- and β-casein and formation of soluble N fractions were retarded by Lc. lactis inoculation. Levels of αs1-casein, β-casein and pH 4·6-soluble N after 60 d were respectively 30·4, 34·9 and 28·8% in cheese made with starter and 18·4, 23·0 and 34·2% in control cheese. More acidic conditions in the interior of cheese made with starter resulted in a reduction of Enterobacteriaceae, coliform and staphylococci counts, which after 60 d were respectively 2·55, 2·40 and 0·29 log units lower than in control cheese. The firmer texture obtained throughout maturation for cheese made with starter was attributed to retarded proteolysis and lower pH value. Cheese flavour quality and intensity were significantly impaired by Lc. lactis inoculation.

The blue cheese nitrogenous fractions soluble in water and in 5% phosphotungstic acid (PTA) were analysed by HPLC after 3–180 d ripening. In the water-soluble fraction, in addition to four or five major peaks corresponding to amino acids, there were many minor peaks, which increased during ripening. The low molecular mass peptides, soluble in 5% PTA, showed ripening-induced increments. A method combining precipitation with 5% PTA, gel permeation and subsequent HPLC was used to isolate some peptides of cheese. Four peptides containing between seven and ten residues were isolated and their amino acid composition and N-terminal residues determined.