The critical flux during ultrafiltration of whey protein concentrate and sodium caseinate suspensions was investigated. The weak form of critical flux was found for both suspensions. Critical flux of sodium caseinate was higher than that of whey protein concentrate. This could be due to the differences in particle size of the suspensions, resulting in a slower particle back transportation for small particles (whey proteins) compared to the larger casein micelles. Critical flux increased as crossflow velocity increased and decreased as concentration increased, suggesting that critical flux was determined by competition between rate of particle removal from the membrane surface and rate of particle movement towards the membrane surface. Influence of changing pH, addition of NaCl and CaCl2 on the critical fluxes of both protein suspensions was also studied. Increasing pH led to an increase in critical flux for both protein suspensions, suggesting that electrostatic repulsive forces are involved in determining critical flux in both cases. Addition of NaCl gave rise to a decrease in electrostatic interactions due to an increase in ionic strength and ζ potential, and resulted in a decrease in critical flux for sodium caseinate, but had no significant effect for whey protein concentrate. Addition of CaCl2 resulted in a decrease in the critical flux and had a more pronounced influence than NaCl. These results suggest that, in addition to electrostatic repulsive forces, other factors such as structure of protein may be involved in determining the critical flux.

The effects, on the yield and composition of the milk of the cow, of additions to the diet of the calcium salts of acetic, propionic, butyric or lactic acids were determined in 3 change-over experiments. In all cases yield of milk was increased slightly and milk fat content was reduced; solids-not-fat (SNF) percentage was depressed by acetate and butyrate. The effects of these treatments differed markedly from those observed previously when dilute solutions of the corresponding acids were infused into the rumen, but the relative effects of the calcium salts were similar to those of the free acids. It was concluded that the specific effects of the acids were overshadowed by a more marked general effect arising from their addition to the diet as calcium salts. This was confirmed in a subsequent experiment with fistulated cows, in which the effect of an infusion of propionic acid into the rumen was compared with that of an infusion of calcium propionate and of calcium propionate given with the diet. The effect of the addition to the diet of calcium in the form of carbonate differed from that of calcium salts of the fatty acids. It was concluded that the salts were not likely to find practical use.

A method is described of measuring pressures in a teatcup assembly using strain gauge transducers and simultaneously following movement of the liner wall by means of a cine camera. In preliminary experiments with a narrow bore type liner it was found that pressures below the teat could vary during a single pulsation cycle from a few inches of mercury below atmospheric pressure (inHg vacuum) to as high as 25 inHg vacuum in the absence of an airbleed. Bleeding air into the barrel of the liner or into the clawpiece considerably reduced fluctuation in pressure, and the vacuum barely rose above the nominal milking vacuum of 15 inHg. Reducing the rate of change of pressure in the pulsation chamber did not greatly affect the maximum vacuum obtained. Opening and closing of the liner by pressure change in the pulsation chamber was under some conditions considerably delayed by the pressure conditions existing inside the liner.

It is suggested that inertia effects of milk in the cluster and the natural frequency of the system are largely responsible for the observed pressure changes under the teat.

The effect of 15 amides and related compounds on the heat stability of milk was investigated; of these urea, biuret, triuret, methyl urea and ethyl urea had a similar stabilizing effect. These 5 compounds reacted with lysine to form a ninhydrin-positive compound, possibly homocitrulline, and with lactose produced Maillard-type browning, but some of the other compounds studied were also capable of participating in one or both of these reactions. The only effect which the 5 stabilizing amides had in common and which the other compounds did not share was a significant pH-buffering capacity in synthetic systems and in milk. It is suggested that urea exercises its stabilizing influence in milk principally through its ability to buffer the pH of the system during heating.

Bovine milk systems were analysed for adenosine 5′-triphosphate (ATP) using the luciferase-ATP reaction in a liquid scintillation counter. Approximately 0·2 µmol ATP/1 milk serum were evident both in whole milks and the corresponding skim-milks. ATP was not detectable in skim-milk ultrafiltrates. These findings indicated that ATP was present in a non-dialysable portion of skim-milk. Centri-fugation of whole milks from individual cows at 5500 g for 15 min at 10°C yielded skim-milks essentially devoid of somatic cells and bacteria. However, the ATP in the skim-milks decreased by less than 20% compared with the whole milks indicating that the calcium phosphate-citrate (CPC)–caseinate micelles were the source of the ATP. ATP was not detectable in colloidal phosphate-free milk, from which CPC had been removed, confirming that the ATP was sequestered in the constituent CPC. Likewise, the occurrence of significant amounts of Mg, another potent stabilizer of amorphous calcium phosphate (ACP) in other biological systems, was confirmed in the colloidal phosphate of milk. From 0·13 to 0·31 µmole ATP/1 (mean, 0·23) was found in the 9 milk samples studied. The discovery of small but appreciable levels of ATP in the CPC of milk provides further evidence for the analogy previously shown to exist between the CPC complex of milk and the ACP which accumulates in mitochondria. The latter has been postulated to provide an essential precursor for crystalline bone salts to form in ordered calcification processes. The implications of these findings in the biosynthesis of milk are briefly discussed.

A global process for the production of goat milk hydrolysates enriched in angiotensin converting enzyme (ACE) inhibitory peptides was proposed. Firstly, the protein fractions (caseins and whey proteins) were separated by ultrafiltration through a 0·14 μm ceramic membrane. The casein fraction obtained in the retentate stream of the above filtration step was subsequently hydrolysed with a combination of subtilisin and trypsin. After 3 h of reaction, the hydrolysate produced presented an IC50 of 218·50 μg/ml, which represent a relatively high ACE inhibitory activity. Finally, this hydrolysate was filtered through a 50 kDa ceramic membrane until reaching a volume reduction factor of 3. The permeate produced presented an improvement of more than 30% in the ACE inhibitory activity. In contrast, the retentate was concentrated in larger and inactive peptides which led to a decrease of more than 80% in its inhibitory activity. The process suggested in this work was suitable to obtain a potent ACE inhibitory activity product able to be incorporated into food formulas intended to control or lower blood pressure. Moreover, the liquid product could be easily stabilised by spray dried if it would be necessary.

1. Data are given on the changes which occurred in the composition of sow's milk during the course of 24 lactations. The mean percentages of the major constituents (192 samples) were: total solids, 20·0%: crude protein, 5·7%: lactose, 4·7%; fat, 8·6% and ash, 0·89%.

2. There were differences in milk composition between sows and between successive lactations, but these were only appreciable for milk fat percentage between sows.

3. A highly significant negative correlation (P < 0·001; r = –0·62) was found to exist between the percentages of protein and lactose in the milk, quite apart from the general trend for protein content to fall with advance in lactation. Possible reasons for this are discussed.

This paper aimed at evaluating the effect of summer transhumance to mountain pastures of dairy cows of different breeds on cheese-making ability of milk. Data were from 649 dairy cows of specialized (Holstein Friesian and Brown Swiss) dual purpose (Simmental) and local (mostly Rendena and Alpine Grey) breeds. The Fourier-Transform Infra-Red Spectra (FTIRS) of their milk samples were collected before and after transhumance in 109 permanent dairy farms, and during transhumance in 14 summer farms (with multi-breeds herds) of the Trento Province, north-eastern Italy. A variety of 18 traits describing milk coagulation, curd firming, cheese yield and nutrients recovery in curd/loss in whey were predicted on the basis of FTIRS collected at the individual cow level. Moving the cows to summer farms improved curd firming traits but reduced cheese yields because of an increase of water and fat lost in the whey. During summer grazing, most of cheese-making traits improved, often non-linearly. The milk from summer farms supplementing cows with more concentrates showed better curd firming and cheese yield, because of lower fat lost in the whey. The breed of cows affected almost all the traits with a worst cheese-making ability for milk samples of Holsteins through all the trial, and interacted with concentrate supplementation because increasing compound feed tended to improve cheese-making traits for all breed, with the exception of local breeds for coagulation time and of Brown Swiss for curd firming time. In general, summer transhumance caused a favourable effect on cheese-making aptitude of milk, even though with some difference according to parity, initial days in milk, breed and concentrate supplementation of cows.

The objective of the study was twofold: (i) to quantify the differences in daily milk yield (DMY) and total milk yield (TMY) between lame and non-lame dairy ewes and (ii) to determine the shape of lactation curves around the lameness incident. The overall study was a prospective study of lameness for the surveyed sheep population, with a nested study including the selection of matching controls for each lame ewe separately. Two intensively reared flocks of purebred Chios ewes and a total of 283 ewes were used. Data, including gait assessment and DMY records, were collected on a weekly basis during on-farm visits across the milking period. A general linear model was developed for the calculation of lactation curves of lame and non-lame ewes, whereas one-way ANOVA was used for the comparisons between lame ewes and their controls. Lameness incidence was 12·4 and 16·8% on Farms A and B, respectively. Average DMY in lame ewes was significantly lower (213·8 g, P < 0·001) compared with the rest of the flock, where DMY averaged 1·340 g. The highest DMY reduction in lame ewes was observed during the week 16 of the milking period (P < 0·001), whereas the reduction of DMY, for lame ewes, remained significant at P < 0·001 level from week 8 to week 28 of milking. Comparisons between lame and controls revealed that at the week of lameness diagnosis a significant DMY reduction (P ≤ 0·001) was observed in lame ewes (about 32·5%), which was maximised 1 week later (35·8%, P ≤ 0·001) and continued for several weeks after recovery, resulting in 19·3% lower TMY for lame ewes for the first 210 d of the milking period (P < 0·01). Moreover, at flock level, TMY for non-lame and lame ewes, as calculated by the general linear model, was 318·9 and 268·0 kg, respectively. The results of this study demonstrate evidence of significant financial losses in dairy sheep due to lameness which, however, need to be accurately estimated in further, more detailed, analyses.

Restrictions regarding the use of antibiotics make selective antibiotic dry cow therapy (DCT) mandatory on organic farms in Germany. This requires methods for identifying cows with an intramammary infection (IMI) at dry-off. The aim of this field study was to create a decision scheme for the use of DCT based on cow level factors associated with IMI at dry-off and the probability of both cure and new infection (NI) during the dry period. Data from 250 cows from five organic farms were collected including somatic cell counts (SCC) from Dairy Herd Improvement (DHI) records, California mastitis test (CMT) results at dry-off, clinical mastitis (CM) history, parity and dry-off treatment. IMI at dry-off were most accurate identified using a geometric mean SCC of 100 000 cells/ml as a threshold at either one or three DHI records prior to dry-off. Using a combination of SCC with either CM history, CMT at dry off or parity slightly increased the sensitivity of detection (SE). The probability of cure of the infection over the dry period increased with use of both antibiotic DCT and application of an internal teat sealant (ITS) and decreased when the dry period was longer than 56 d. The risk of NI decreased with the use of ITS and infections with minor pathogens at dry-off. Compared with the selection performed by the farmers during the study period identification of IMI based on the selection criterion with a defined SCC threshold achieved a higher SE.

1. Full-cream unsweetened condensed milk (evaporated milk) and full-cream sweetened condensed milk (condensed milk) were prepared simultaneously on several occasions each time from a common bulk of raw milk. Heat treatment in the preparation of evaporated milk is, of course, much more severe than with condensed milk.

(a) There was no loss of vitamin A, carotene or riboflavin in either of the processes.

(b) The mean loss of vitamin C as compared with the raw milk was 10% for condensed and 60% for evaporated milk.

(c) The vitamin B1 losses were 3·5 and 27% respectively.

(d) Tests on rats showed that the biological values and true digestibilities of the proteins of the raw, condensed and evaporated milks were respectively 85·6 and 94·2, 84·6 and 98·8, 84·1 and 93·7. The differences in biological value are without statistical significance but the digestibility of the condensed milk was significantly higher than that of the other two milks.

Agents that increase natural protective mechanisms have been proposed for prevention and treatment of intramammary infections. The objective of this study was to describe the effects of a single intramammary infusion of a lipopolysaccharide (LPS)-based biological response modifier (BRM) on cellular death mechanism in uninfected and Staphylococcus aureus-infected bovine mammary glands during involution. Three groups of 12 cows, each one including 6 Staph. aureus-infected and 6 uninfected, were infused in two mammary quarters with BRM or placebo and slaughtered at 7, 14 and 21 d of involution. In infected quarters, BRM treatment produced a significant increase in percent of stained epithelial cells for the apoptosis-promoting protein Bax at every observation period. In addition, BRM produced a significant increase of immunostained stromal cells for Bax compared with placebo-treated quarters. BRM treatment produced an increase in percentages of epithelial cells staining with active caspase-3 at 7 d and 14 d of involution compared with placebo-treated quarters and a significant decrease in percentages of terminal deoxynucleotidyl transferase dUTP nick end labelling (TUNEL)-positive epithelial cells at 7 d and 21 d of involution. In addition, BRM treatment caused an increase in percentage of stromal cells immunostaining for active caspase-3 and TUNEL. An increase of active caspase-3 and TUNEL epithelial and stromal cell immunostaining was observed in Staph. aureus-infected compared with uninfected quarters. Cellular proliferation, determined by Ki-67 immunostaining, was increased in epithelial and stromal cells from Staph. aureus-infected compared with uninfected quarters at every observation period. These results provide new insights into the mechanism of mammary cell death in uninfected and Staph. aureus-infected bovine mammary gland during involution and illustrate the effects of LPS-based BRM on apoptosis and cell proliferation during mammary involution.

The proteolytic stage of the digestion process of white cheese curd was optimised to maximise the angiotensin I-converting enzyme (ACE)-inhibitory activity of the final enzyme-modified cheese (EMC) paste. It was found that bioactive peptides generation in EMC paste was of multi-variable dependent nature and could be optimised by targeted selection of specific component variables. Maximum ACE-inhibitory was obtained by proteolysis at 48 °C for 25 h with 1 g Flavourzyme/kg cheese curd. This bioactive EMC paste was subsequently spray-dried. The drying conditions were optimised to obtain a highly soluble powder to warrant quick and complete hydration, with the lowest water activity to maximise long term storage. The higher the inlet drying air temperature, the greater was the solubility of resultant EMC powder. Differential scanning calorimetry analysis revealed that the highest drying air temperature (200 °C) resulted in a lower glass transition temperature for the potentially bioactive EMC powder.

Various methods were used to study 42 Gram-positive cocci belonging to the family of Micrococcaceae and isolated from dairy products. Only a few strains could be identified using the ATB 32 biochemical micromethod rapid gallery system (API). All strains were subjected to conventional biochemical tests. The results were then analysed by a numerical method using the Sokal–Michener similarity coefficient. The 42 strains were distributed into 10 clusters at the Euclidean distance of 3·2. Most (75%) of the isolates were identified at the species level, but Micrococcus luteus could not be differentiated from Mc. lylae within the Micrococcus genus. An identification method based on the analysis of ribotype patterns was then applied to the isolates and these were compared with the patterns of collection strains. Cellular DNA was cleaved by the restriction enzymes SacI and KpnI and probed with the peroxidase-labelled 16S+23S rRNA of Escherichia coli. Ribotype patterns were analysed using a Dice coefficient and the unweighted pair group method using arithmetic averages, making dendrogram construction possible. Of the strains investigated, >84% were characterized to the species level. The remaining strains were found to belong to the Arthrobacter group or were atypical Micrococcus species. Of the isolates, 52% belonged to Micrococcus luteus, 17% were identified as Kocuria varians and 7% were assigned to the Brachybacterium genus.

The need to improve the shelf life and quality of foods, combined with the urgency to reduce waste generated by synthetic non-biodegradable packaging, have resulted in an increasing interest in biodegradable or edible materials (Chen, 1995). The challenge in the development of such materials lies in achieving controlled lifetime together with compatibility with foods and the environment. Natural polymers or polymers derived from natural monomers such as food proteins offer the greatest opportunities, since their biodegradability and environmental compatibility are assured (Krochta & de Mulder-Johnston, 1997).

Milk proteins such as caseins have been formulated into coatings and films for improving food quality (Baker et al. 1994). Unfortunately, the highly hydrophilic nature of these proteins limits the possibility of producing films with the required properties. Gamma irradiation, which induces the formation of crosslinks in the protein structure, is known to improve the mechanical properties and water resistance of such materials (Brault et al. 1997; Mezgheni et al. 1998a; Ressouany et al. 1998), and can also sterilize materials for possible biomedical applications (Kaetsu, 1995).

Gamma irradiation is slowly becoming accepted in the food industry as a means of safely improving the shelf life of various fruits and vegetables and eliminating bacterial contamination in meats (Pszczola, 1997). All these features (sterility, increased mechanical strength, controlled life time) make gamma irradiation a promising technique for the production of commercial biodegradable films.

In the present study, we have investigated the microbial resistance of calcium caseinate films irradiated at 4 or 64 kGy. A minimum dose of 4 kGy was required to produce complete sterility in the films without inducing many crosslinks in the protein. A dose of 64 kGy was used to induce maximum crosslinking density (Ressouany et al. 1998). The rate of modification of the films was evaluated using three methods. Firstly, microbiological counts were performed on films incubated with a strain of Pseudomonas aeruginosa. This strain was chosen because it produces a wide range of proteinases and is often implicated in the process of food spoilage. These results were compared with those obtained for soluble N. Since conversion to CO2 is one of the standard test procedures to assess biodegradability (El-Din Sharabi & Bartha, 1993), we also analysed the CO2 produced by the biodegradation of the crosslinked films using a modified version of a standard test procedure (American Society for Testing Materials, 1992). This measures the aerobic degradation of plastic materials inoculated with municipal sewage sludge. We have replaced the sludge by a concentrated bacterial strain (Ps. aeruginosa) and compared these results with the two previous methods. This last method was used to measure the resistance of the crosslinked films to bacterial degradation.

The concentrations of lactose, glucose, glucose 6-phosphate, glucose 1-phosphate, UDPglucose, UDPgalactose, UDP, UMP, inorganic phosphate, ADP and AMP (metabolites involved in the lactose synthesis pathway), and cAMP, galactose and sodium were measured in the mammary secretion from four or five mammary glands on each of six sows during the first 5 d post weaning. The concentrations of lactose, glucose and galactose were also measured in plasma during this time. Following weaning, the rapid increase in the concentrations of glucose 6-phosphate and UDPgalactose suggested that the rate of lactose synthesis was regulated by the inhibition of hexokinase and/or lactose synthase, while the decrease in glucose and AMP indicated a subsequent decline in glucose and ATP utilization. The rapid increase in glucose 6-phosphate which plays a pivotal role as a substrate for both lactose and de novo fatty acid synthesis, and the rapid decrease in AMP which reflects ATP utilization, were good markers of decreased metabolic activity. These rapid changes in the metabolic activity of the mammary glands were not observed in a second weaning study when two piglets were removed from selected mammary glands for periods up to 5 h during established lactation. Since concentrations of lactogenic hormones remain elevated following partial weaning, but fall following total weaning (Rojkittikhun et al. 1991), these differences in mammary gland metabolism indicate that endocrine rather than autocrine mechanisms are controlling lactose and fat synthesis during the initial stages of total weaning.

Published data are available for the fatty-acid compositions and molecular-weight distributions of triglycerides in milk and adipose tissue from the guinea-pig, rat, mouse and rabbit, and in milk from the human, cow, mink and hamster. These data have been used to calculate the extent of non-random associations of fatty acids of different chain lengths in these triglycerides.

The results support, in general, the concept of non-correlative acylation, i.e. that during the biosynthesis of these triglycerides, fatty acids already present on the glycerol backbone do not influence the selective acylation of subsequent fatty acids. However, milk triglycerides from these animals show varying degrees of intermolecular specificity which can be explained in terms of positional specificity of fatty acids on the glycerol backbone.

Treatment of milk with 0·05% (w/v) H2O2 for 8 h at 24°C had no significant effect on the concentrations of seven of the B-complex vitamins or of the fatsoluble vitamins A and E or of carotene. Rat tests showed that the nutritive value of the milk proteins was slightly reduced. This finding was confirmed by microbiological tests with Streptococcus zymogenes, which also showed that the loss was probably connected with that of methionine. The concentration of H2O2 used was effective in controlling bacterial growth during the incubation period, even in a sample of milk with a high initial bacterial count.

(1) 419 samples were counted in each of ten stations (laboratories) in order to assess the accuracy of the plate-count method under the conditions existing in practice.

(2) When, in each count, that plate which would ordinarily be used in practice is selected for the final count, it is found that the range which would include 95 per cent, of counts in the same sample is as wide as from one-ninth of the mean to nine times the mean when inter-station differences are taken into account. For 80 per cent, of counts in the same sample the corresponding range would be from 1/(4·1) of the mean to 4·1 times the mean.

(3) Systematic differences between stations under these conditions account for between 3 and 4 per cent, of the total experimental variation.

(4) When thirty-one complete samples in which all counts were made at a dilution of 1/10 were statistically analysed separately it was found that the range which would include 95 per cent, of counts in the same sample was from 1/(3·7) of the mean to 3·7 times the mean. For 80 per cent, of counts in the same sample the corresponding range would be from 1/(2·3) of the mean to 2·3 times the mean. There were no systematic station differences.

(5) When all plates are counted at the same dilution the error is therefore much reduced and this result suggests that the systematic station differences exhibited by the 419 samples as well as some of the random errors occurring in them is due to the combining of plate counts made at different dilutions.

In effect this means that owing to the different conditions encountered during transit comparable figures for any sample could not be expected.

Fermented milk is known to possess potent antioxidant activity. The present study was undertaken to assess the preventive effect of fermented camel milk (FCM) prepared using lactococcus lactis subsp. cremoris against CCl4 induced kidney damage in mice. Nephrotoxicity was induced in mice by a single dose of CCl4 (10 ml/kg 0·3% olive oil, ip). Female mice were pretreated daily with FCM for 15 d. Renal damage was associated with an increase in oxidative stress parameters (lipid peroxidation, protein carbonyl and changes in antioxidant enzyme activities and non-enzymatic antioxidant) and nephropathology markers.

The renal injury induced by CCl4 was confirmed by the histological study of the CCl4-intoxicated mice. Pretreatment with FCM significantly prevented renal dysfunction by reducing oxidative stress, while mice recovered normal kidney histology. Moreover, FCM prevented toxicity biomarker changes by reducing creatinine, urea, uric acid, lactate dehydrogenase (LDH) and electrolytes levels in plasma. These data indicate that FCM is efficient in inhibiting oxidative stress induced by CCl4, and suggests that the administration of this milk may be helpful in the prevention of kidney damage.