Manipulations of the lactation cycle are achieved through nutritional regimens and generally result in a restriction of the physiological lactation cycle. Most models of lactation used in management programmes only describe the average time course of lactation for groups of cows on a given feeding regimen. This is inadequate for the variety of feeding systems in use on British farms. In the present paper several existing models of lactation have been critically evaluated. An integral equation approach has been developed to rationalize experimental observations and currently accepted biological concepts.

Teat penetration into transparent silicone rubber teatcup liners was recorded during milking of 90 cows on 15 farms. The cows were of Norwegian Red Cattle breed with mean teat length close to the average for the breed. The mean teat length was 54 and 48 mm for fore and rear teats respectively, and mean penetration at the end of milking was 104 and 94 mm. No significant correlation between initial teat length and teat elongation (difference between penetration and initial length) was found. This indicated that the teatcup liner was more stable on long teats than on short. The distribution of teat penetration at the end of milking showed that a large proportion of fore teats penetrated too far into the liner at the end of milking. The optimal liner length for Norwegian Red Cattle was ~ 150 mm.

A field survey with 70 cows in 15 herds was carried out to find a possible correlation between the depth of teat penetration into the teatcup liner during milking, and udder health. The investigation showed that the depth of penetration into the liner of fore teats was positively correlated with the fore teat end hardness (P < 0·01), and with the frequency of clinical mastitis for the whole udder (P < 0·1). The investigation also showed that the teat end height above the floor was negatively correlated with mean cell count for the previous year (P < 0·001), and with the prevalence of subclinical mastitis in rear quarters (P < 0·05).

Free and protected soya oil and soya oil fatty acids were included in the rations of dairy cows and from outputs in the milk of 18:1 trans and of polyunsaturated acids conditions in the rumen have been deduced. Similarly, the content of citrate in the milk has been used to evaluate changes occurring in the synthesis of fatty acids in the mammary gland.

Buffalo milk collected within 4 h of milking was standardized (4·5% fat and 8·5% SNF) and processed in an ultra high temperature plant at 5 °C intervals. Changes in viscosity, free tyrosine and sedimentation were measured over 6 months at 15 and 30 °C. We suggest that an interaction probably occurred in the casein and whey proteins (β-lactoglobulin) and caused changes in the physical and chemical qualities of these milks during storage. Variations in the casein particle sizes were observed in the milks during storage by electron microscopy.

An indirect enzyme-linked immunosorbent assay was successfully developed for the detection of defined amounts of cows' milk (1–50%) in sheeps' milk and cheese. The assay used polyclonal antibodies raised in rabbits against bovine caseins (BC). The anti-BC antibodies were recovered from the crude antiserum by immunoadsorption and elution from a column containing BC. The antibodies were biotinylated and rendered cows' milk specific by mixing them with lyophilized ovine and caprine caseins. ExtrAvidin-peroxidase was used to detect the biotinylated anti-BC antibodies bound to BC immobilized on 96-well plates. Subsequent enzymic conversion of substrate gave clear absorbance differences when assaying mixtures of sheeps' milk and cheese containing variable amounts of cows' milk.

The nitrogen solubility index (NSI) method for the examination of caseinates was evaluated. It was found that widely scattering NSI values are mainly due to ineffective centrifugation and filtration of the caseinate dispersion. In order to avoid this, an improved combined centrifugation–filtration procedure was developed as an alternative to the original NSI method, using an Amicon micropartition system MPS-1 equipped with discs of filter paper. The micropartition devices can be centrifuged in a Gerber centrifuge of the type used for butyromctric fat determination. Several types of caseinates were evaluated with the new method and yielded a markedly smaller range of single values than were obtained with the NSI method.

Changes in heat stability and Ca2+ activity of recombined concentrated milk (18% solids non-fat:8% fat) induced by the additions of 0·011–0·217 mol phosphate/kg skim milk solids (SMS), 0·022–0·217 mol citrate/kg SMS, 0·011–0·022 mol Ca/kg SMS and 0·016–0·067 mol EDTA/kg SMS were evaluated. Heat stability was assessed using an objective method which involved determination of viscosity after heating under controlled conditions. Low levels of added phosphate and citrate generally effected an acid shift of the viscosity–pH profile, while higher levels caused a broadening of the profile. Addition of CaCl2 at a level of 0·011 mol/kg SMS resulted in a narrowing of the viscosity–pH curve; additions of higher levels resulted in a non-heat stable recombined milk concentrate. EDTA also caused a narrowing of the viscosity–pH curve. The results highlight the importance of pH control for effective stabilization of recombined milk concentrates by additions of phosphate and citrate.

Cream feathering was studied in sixteen samples made from six brands of filter coffee. We have used a predictive rule, deduced from our studies of instant coffees, to determine the likelihood of feathering occurring in filter coffee samples upon the addition of coffee cream. The predictive rule makes use of 1,3,4,5-tetra-hydroxycyclohexane carboxylic acid-3-[(3,4) dihydroxycinnamate] (chlorogenic acid) concentration in the coffee, and the ratio of ultraviolet absorbances at 261 nm and 340 nm. We found good agreement between the predicted and observed behaviour of samples of filter coffee and conclude that the predictive rule is reliable for both instant and filter coffees. The effect of increased fat content in the cream was also studied.

The microorganisms present in raw and pasteurized milk and the sources of contamination in the milk after it had arrived at the processing plant in Addis Ababa were studied. The lowest count registered for raw milk samples was 4 × 107 cfu/ml while the highest was 1 × 109 cfu/ml. Pasteurized milk had mesophilic aerobic counts of 7 × 105 cfu/ml as it left the pasteurizing unit, but the population increased 2- to 4-fold as a result of subsequent contamination. Of the total counts in raw milk, psychrophilic, thermoduric and thermophilic organisms made up 98·l, 1·4 and 0·5% respectively. In pasteurized milk, the amounts were 53·0, 39·5 and 7·5% respectively. Samples of milk pasteurized in the laboratory contained only 74·5% thermoduric and 25·5% thermophilic organisms. The isolates mostly belonged to the genera Bacillus, Streptococcus, Lactobacillus, Arthrobacter, Alcaligenes, Aeromonas and Pseudomonas. Cocci were more predominant than rod-shaped bacteria. Of the rod-shaped bacteria, 73% were Gram-negative. The utensils holding the raw and pasteurized milk and the plastic sheets used for bagging the pasteurized milk contributed unusually high numbers of bacteria which were either thermoduric or thermophilic. More isolates were obtained from the pasteurized than the raw milk. The keeping quality of the pasteurized milk was found to be much lower than that of the laboratory-pasteurized milk.

Samples of UHT milk were contaminated at two levels (102 and 104 cfu/ml) with 52 bacterial strains associated with spoilage. Samples were assayed, using various tests, to determine efficiency in detecting non-sterility after an incubation period shorter than that advised in standard procedures. The tests performed were colony count, titratable acidity and pH modification, organoleptic assessment, stability towards ethanol (68, 80 and 88% v/v), resazurin and nitrate reduction. After 3 d incubation at 30 °C every case was detected by the resazurin test with a good statistical probability (P = 0·999). Reliability was not so high in all other tests, even after 14 d incubation.

Prolidase activity from cytoplasm of Lactococcus lactis subsp. cremoris (Streptococcus cremoris) AM2 was partially purified. The enzyme had Mr 42000 and optimum activity between pH 7·35 and 8·25 in citrate, phosphate and borate buffers while in a universal buffer system an optimum pH between 8·3 and 9·0 was observed. The activity was strongly inhibited by the chelating agents E.DTA, 1,10-phenanthroline and 8-hydroxyquinoline. Inhibition was also noted with dithio-threitol, N-ethylmaleimide and bacitracin. The enzyme was active on all amino-acylproline substrates tested except Gly-Pro and Gip-Pro and also showed activity against Pro-Pro. While most prolyl amino acids tested were not hydrolysed, hydrolysis was noted with Pro-Ala and Pro-Val. Km values of 20 mM and 10 mM were obtained with Phe-Pro and Met-Pro respectively; however, substrate inhibition was observed with Ile-Pro and Leu-Pro.

The protective effect of feeding milk fermented with a mixture of Lactobacillus casei sp. and Lb. acidophilus sp. against Salmonella typhimurium infection in mice was compared with that obtained feeding milks fermented with these microorganisms individually. The survival rate obtained after oral infection with Sal. typhimurium was 100% in mice pretreated by feeding during 8 d with the mixture of Lb. casei and Lb. acidophilus fermented milks. Similar treatments with the individual milks were ineffective. Moreover, mice became more susceptible to infection with Sal. typhimurium after such treatment. The colonization of liver and spleen with the pathogen was markedly inhibited by the pretreatment with the mixture of fermented milk, while such inhibition was not observed using the Lb. casei and Lb. acidophilus milks. The highest levels of anti-salmonellae antibodies in serum and in intestinal fluid were found in the group of mice fed with the mixture and with Lb. casei fermented milk respectively. However, this latter milk was not effective in protecting against Sal. typhimurium. When the mice were first infected with Sal. typhimurium and then fed with the mixture of fermented milks, pathogen colonization was not prevented. The results suggest that the augmentation of resistance to salmonellae caused by the treatment with Lb. casei-+Lb. acidophilus-fermented milk was due to the anti-salmonellae protective immunity mainly mediated by the mucosal tissue. Milk fermented with this mixture could be used as an immunobiological method to prevent gastrointestinal infection.

Physical properties of aerated, high moisture and low calorie table spreads are considerably influenced by the phase volumes of the mix components. Using a statistical approach developed for mixture experiments, the firmness values of milk fat-based table spreads at three different temperatures were quantified in terms of the phase volumes of the fat, water and gas present. A simple equation was found which related changes in relative firmness values with composition at any temperature. Absolute firmness values may be obtained from relative values by multiplying by a factor, F, which is the firmness value of the similarly treated milk fat. This factor is related to the solid fat content by the formula F = 10ks+c, where F is the firmness value in kg cm–2 of milk fat having a percentage solids content, s, k is the slope of a semi-logarithmic plot and c is a constant.

Changes in a Greek traditional soft cheese, Kopanisti, were followed during ripening. Mature cheese contained > 52% moisture, 22·7% fat and 19·3% protein. The as-casein content was hydrolysed faster than the β-casein so that in mature cheese only 23% and 35% respectively of these proteins remained intact. Soluble N, TCA-soluble N, amino acid N and NH3 were present to the extent of 28·9, 24·6, 14·3 and 6·6% of total N respectively. Leucine, γ-aminobutyric acid, valine and alanine were the dominant free amino acids in the mature cheese. Lipolysis was intense and the total free fatty acid content of ripe cheese was ∽ 50 g/kg cheese. The rate of liberation of short-chain (C4–C8) fatty acids was higher than that of the long-chain. The characteristic rich flavour and peppery taste appeared after 16 d ripening and the best overall cheese quality was produced after 32 d maturation.

There are estimated to be 600000 camels (Camelus dromedarius) in Kenya (Wandera, 1985). Almost 80% of these are kept by pastoral tribes living in arid areas in eastern and north-eastern parts of the country. In these regions, camels are important dairy animals. A camel in north-east Kenya can be expected to yield about 4 kg milk daily as compared with 0·5–1·5 kg for a cow in the same area. Most of the camel milk is consumed in the form of fermented milk. The milk is allowed to ferment naturally at ambient temperature and without prior heat treatment until it turns sour. The resulting fermented camel milk is known as Susa. Due to the spontaneous nature of the fermentation, this traditional method results in a product with varying taste and flavour and is often of poor hygienic quality, in addition, because of the limited scale of production, the product can be sold only in the immediate vicinity of the herd. For production of fermented milk under controlled conditions, thermophilic or mesophilic lactic acid cultures are normally used. In warm countries, mesophilic lactic cultured milk offers some advantages, as it can be incubated at ambient temperature (20–30 °C) and the fermentation stops at 1–1·2% lactic acid, eliminating the need for cooling to stop further souring as occurs in the case of yoghurt (Kurwijila, 1980).