Whole milk from cows was concentrated 2-fold by reverse osmosis in a small pilot scale apparatus. All the main constituents of the milk were retained in the concentrate.

The experiment showed that protein was a major cause of blocking of the membrane. Laboratory trials were therefore made on the ultrafiltration of milk to remove the protein with the aim of developing a 2-stage process for the concentration of milk by ultrafiltration followed by reverse osmosis with subsequent recombination of the concentrates from the 2 operations. The rates of both processes and the retentions of the constituents of milk by the membranes were measured.

The use of a silica-based ion-exchange medium for the recovery of protein from wheys prepared by treatment with rennet or with acid has been investigated. The protein capacity of the medium whilst maintaining an adsorption greater than 75% during the passage of rennet-and acid-whey was 0·079 and 0·053 g/g respectively. Bovine serum albumin (BSA), α-lactalbumin (α-la) and β-lactoglobulin (β-lg) adsorbed from acid-whey were mostly recovered in yields greater than 93% in an undenatured form essentially free of lactose and milk salts by elution using 0·1 M-HC1. With rennet-whey, BSA and part of the α-la were not recovered in the native form, probably because of proteolysis during elution by enzymes originating in the rennet used in the manufacture of the whey. There was, however, no effect on the recovery of native β-lg adsorbed by the medium. An unidentified proteinaceous fraction, thought to be of casein origin, was also adsorbed and recovered from rennet-whey. Fractions of the adsorbed proteins could not be obtained by eluting with a gradient increase in NaCl concentration. Nevertheless, purified β-lg was obtained by passing a large quantity of whey through the medium. This protein had a high affinity for the functional groups of the medium, to the extent that other proteins initially adsorbed were subsequently displaced. Unidentified proteinaceous material in rennet-whey also had a high affinity for the functional groups of the ion exchanger but most of this fraction could be removed by a pretreatment procedure which involved passing the whey through the medium at pH 5·0; unidentified material was selectively adsorbed at this pH. The medium could also be used to produce a fraction containing a mixture of BSA and α-la but it was not possible to separate these proteins.

Listeria monocytogenes survived and, under most conditions, multiplied when inoculated directly into the cheese milk of laboratory made Camembert cheeses. The rate and extent of growth was reduced at lower storage temperatures. Significantly higher rates of growth occurred at the surface compared with the centre of the cheeses, and these were probably associated with increased pH and proteolysis at the cheese surface due to the mould ripening process. Similar results were obtained with Camembert cheeses surface inoculated after manufacture. There was also temperature-dependent growth of List, monocytogenes on a range of inoculated commercially manufactured soft cheeses. Significant growth occurred in Cambazola, French and English Brie, blue and white Lymeswold, French Camembert and Brie with garlic. Little if any growth occurred in blue and white Stilton, Mycella, Chaume and full fat soft cheese with garlic and herbs at the temperatures examined.

The concentration ranges in milk and cheese of a number of metallic elements relevant to the health of the consumer are dependent upon animal species, feeding, time of year, environmental conditions and manufacturing processes. We have measured the concentrations of selected trace elements – Al, Ba, Cd, Co, Cr, Cu, Fe, Mg, Mn, Ni, Pb, Pt, Sr and Zn – in raw ewes' milk and typical ewes' milk cheeses. Samples of milk, curd, whey, cheese after moulding, cheese after salting, commercial cheese (Pecorino), Ricotta, scotta and brine were analysed for seven complete cycles of cheese production. Samples of curd, whey, brine and waste product (i.e. scotta) were collected and analysed in addition to the cheese and milk to assess the distribution of each element in the main product, by-products and waste products during cheesemaking. Quantitative determinations were performed mainly by inductively coupled plasma atomic emission spectrometry. There were considerable differences among the trace element contents of raw ewes' milk and related products, indicating that manufacturing processes play a key role in the distribution of minor and trace elements. Two different approaches were used to assess the dietary intake of these elements associated with the consumption of Pecorino and Ricotta, and whether this had any nutritional or toxicological implications. The results indicated no toxicological risk and showed that, on the contrary, Pecorino may be a good source of several essential elements.

The effects of cold storage at 4 °C for 12, 24 and 48 h on the physicochemical characteristics and renneting properties of ewes', goats' and cows' milks were compared. The most important changes were observed in cows' milk. Soluble calcium concentrations were not affected in ewes' milk but were increased by 10% in cows' milk and 7% in goats' milk. More casein was dissociated on cooling cows' (+300%) than goats' (+100%) milk, and there was no change in soluble casein in ewes' milk. The coagulation characteristics of cows' milk were more impaired by cold storage than goats' or ewes' milks. Coagulation times increased by ∼30% and whey draining capacity decreased by 40% after cows' milk was cooled, but there were no changes with ewes' milk and only a slight decrease in coagulation time with goats' milk. We propose an interpretation of these results based on the physicochemical properties of each type of milk.

The effects of daily supplements of 300 g native and 2 hydrogenated cod-liver oils (CLO) to the diets of lactating cows have been examined. Native CLO supplements increased the proportion of propionate and decreased the proportion of acetate in the rumen and also decreased the yields in milk of fatty acids synthesized within the mammary gland and those derived from plasma triglycerides. These effects were reduced or eliminated when the hydrogenated oils were given instead of the native CLO. With all 3 supplements about 15% of the dietary C20and C22 acids was secreted in milk.

Both native and hydrogenated CLO supplements increased the concentrations of the cholesteryl ester and phospholipid components of the α-lipoproteins in the blood plasma. These components contained most of the C20 and C22 acids of the CLO supplements that were incorporated into the blood plasma lipids. With the native CLO supplement about half of the C20 and C22 acids present in the blood plasma were polyunsaturated.

There were no differences in the effectiveness of high-density plasma lipoproteins as activators of triglyceride emulsions for lipoprotein lipase hydrolysis whether the lipoproteins were from cows receiving the native or the hydrogenated CLO supplements or the control diets. Significant rates of hydrolysis by lipoprotein lipase could not be demonstrated using as substrates low- or high-density plasma lipoproteins or activated emulsions of their extracted lipids.

Additional in vitro experiments using activated triglyceride emulsions as substrates for mammary lipoprotein lipase showed that replacement of a soybean oil emulsion by an emulsion of native CLO reduced the rate of hydrolysis considerably, whereas an emulsion of hydrogenated CLO was without effect unless it was present at levels in excess of 50%.

It is concluded that the change in rumen fermentation induced by the polyunsaturated fatty acids of CLO is implicated in the decreased intramammary synthesis of fatty acids, but that additional information is required before the reason for the reduced mammary uptake of plasma fatty acids can be established.

During a 12-month longitudinal study, bulk-tank milk was collected from organic (n=17) and conventional (n=19) dairy farms in the UK. Milk samples were analysed for vitamin A (retinol), vitamin E (α-tocopherol) and β-carotene content. The farming system type, herd production level and nutritional factors affecting the milk fat vitamin content were investigated by use of mixed model analyses. Conventionally produced milk fat had a higher mean content of vitamin A than organically produced milk fat, although there were no significant differences in the vitamin E or β-carotene contents between the two types of milk fat. Apart from farming system, other key factors that affected milk fat vitamin content were season, herd yield and concentrate feeding level. Milk vitamin content increased in the summer months and in association with increased concentrate feeding, whilst higher-yielding herds had a lower milk vitamin E and β-carotene content. Thus, conventional dairy farms in the UK produced milk with a higher vitamin A content, possibly owing to increased vitamin A supplementation in concentrate feeds. However, knowledge of the effects of season, access to fresh grazing or specific silage types and herd production level may also be used by all producers and processors to enhance the vitamin content in milk.

The solubility of milk protein concentrate (MPC) powders was influenced by the method used for preparing the concentrate, drying conditions, and the type of dryer used. Increasing total solids of the ultrafiltered concentrates (23% total solids, TS) by diafiltration to 25% TS or evaporation to 31% TS decreased the solubility of MPC powders (80–83% protein, w/w dry basis), with ultrafiltration followed by evaporation to higher total solids having the greater detrimental effect on solubility. High shear treatment (homogenisation at 350/100 bar, microfluidisation at 800 bar or ultrasonication at 24 kHz, 600 watts) of ultrafiltered and diafiltered milk protein concentrates prior to spray drying increased the nitrogen solubility of MPC powders (82% protein, w/w dry basis). Of the treatments applied, microfluidisation was the most effective for increasing nitrogen solubility of MPC powders after manufacture and during storage. Manufacture of MPC powders (91% protein, w/w dry basis) prepared on two different pilot-scale dryers (single stage or two stage) from milk protein concentrates (20% TS) resulted in powders with different nitrogen solubility and an altered response to the effects of microfluidisation. Microfluidisation (400, 800 and 1200 bar) of the concentrate prior to drying resulted in increased long term solubility of MPC powders that were prepared on a single stage dryer but not those produced on a two stage spray dryer. This work demonstrates that microfluidisation can be used as a physical intervention for improving MPC powder solubility. Interactions between the method of preparation and treatment of concentrate prior to drying, the drying conditions and dryer type all influence MPC solubility characteristics.

A study of 799 cultures of staphylococci and micrococci, isolated mainly from milk, showed that according to their general character the strains could be arranged in a virtually continuous series. At one extreme is the pathogenic staphylococcus and at the other a thermoduric saprophyte. The series consists of three main groups:

(1) The staphylococcus group in which the organisms are sugar fermenters and relatively sensitive to heat. They are, mainly at least, parasites of the animal body. Four subgroups are distinguishable. In three ammonia is formed from arginine, and in two acetoin is formed from glucose. A test for acetoin production defines those mannitol fermenters which do not produce coagulase.

(2) An intermediate group in which the organisms are obligate aerobes and do not produce acid from sugars.

(3) The dairy micrococci, a group of thermoduric sugar fermenters which occur frequently on dairy equipment and in pasteurized milk. The group comprises two species conforming to Micrococcus luteus Cohn emend. Lehmann & Neumann, and M. varians (Dyar) Migula.

Classical methods and methods based on the use of disodium ethylene-diaminetetra-acetate (EDTA) for the semi-micro determination of calcium and magnesium in milk and milk diffusate are described. With both types of method satisfactory accuracy and precision are attainable. The use of the EDTA methods leads to greater speed and convenience but practice in recognizing the correct titration end-points is necessary.

The somatic cell count (SCC) in milk is associated with increasing proteolytic degradation of caseins and it has been suggested that enzymes derived from somatic cells contribute to a lower yield and poorer quality of cheese. It is essential to increase the knowledge on naturally occurring milk proteinase activities to better understand how to improve the technological quality of milk. The aim of this work was to identify peptides actually present in milk as a result of proteolysis at different levels of SCC and to assign these peptides to potential responsible proteases where possible. Peptide fractions were prepared from acid whey by ultrafiltration at a molecular cut-off value of 10 000 Da. The peptides were separated using capillary reversed phase high performance liquid chromatography (RP-HPLC) and identified by matrix-assisted laser desorption/ionization-time of flight tandem mass spectrometry (MALDI-TOF MS/MS). Peptides identified ranged in mass from 1023 to 2000 Da, and originated from αS1-, αS2- or β-casein. Possible responsible proteases that could be suggested when examining the peptide cleavage sites included plasmin, cathepsin B, D and leukocyte elastase. The results indicated that plasmin was primarily responsible for the observed proteolysis in milk at low cell count, whereas the cathepsins and elastase became implicated at elevated cell count. Specificity and activity of cathepsins and elastase has earlier mainly been studied in model systems, whereas less is known about their activities in milk itself. This is also the first indication of involvement of elastase in milk proteolysis through the unequivocal determination of cleavage sites.

The lipoprotein lipase and tributyrate hydrolysing activities were found to be similarly distributed in the fractions obtained when whole milk was separated into skim-milk and cream, and when the cream was washed and freed from lipid. These enzyme activities in skim-milks and in extracts of lipid-free cream could not be separated by affinity chromatography on heparin-Sepharose. The enzymes were inactivated to the same degree when incubated at 37°C in the presence of 1·5 M-NaCl, pH 8·5, and both showed the same marked decrease in stability at 4°C in 1·5 M-NaCl, when the pH was changed from 8·3 to 9·0. Irradiation of skim-milk with UV-light caused the same decrease in both lipoprotein lipase and tributyrate hydrolysing activities. An antiserum against a highly purified skim-milk lipoprotein lipase caused total inhibition of the lipoprotein lipase and tributyrate hydrolysing activities in skim-milk and in extracts of lipid-free cream. It is suggested that in bovine milk there is only one major lipase and that it is identical to lipoprotein lipase.

Kefir is a fermented-milk beverage originating and widely consumed in the Caucasus as well as in Eastern Europe and is a source of bacteria with potential probiotic properties. Enterohaemorrhagic Escherichia coli producing Shiga toxin is commonly associated with food-transmitted diseases; the most prevalent serotype causing epidemics is Esch. coli O157:H7. The aim of this study was to evaluate the antagonism of Lactobacillus plantarum isolated from kefir against the action on Vero cells of supernatants of the Esch. coli O157:H7 strain 69160 expressing the type-II Shiga toxin (Stx2) and to study the role of the Lactobacillus cell wall in that inhibition. Spent culture supernatants of Esch. coli O157:H7 strain 69160 led to cytotoxic effects on cultured eukaryotic cells as evidenced by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium-bromide–cleavage assay or by lactate-dehyrogenase release. Lb. plantarum CIDCA 83114 reduced the cytotoxic activity of Stx present in strain-69160 supernatants, and this protection was markedly higher than those of Lactobacillus kefir CIDCA 83113 and 8348 and Lb. delbrueckii subsp. bulgaricus CIDCA 333. This antagonism of cytotoxicity was mimicked by Lb. plantarum cell walls but was reduced after heating or protease treatments, thus indicating a protein or peptide as being involved in the protection mechanism. The cell surface of the lactobacilli bound the subunit B of Stx thereby decreasing the cytotoxicity. These interactions could constitute the first step in preventing the damage induced by Esch. coli O157:H7 supernatants, thus representing a valuable means of potentially mitigating the noxious effects of this food pathogen.

Cathepsin D, the principal indigenous acid proteinase in bovine milk, is a lysosomal proteinase, which exists in milk in four forms, including the inactive zymogen procathepsin D. The thermal inactivation kinetics of bovine cathepsin D, isolated from spleen and milk, were studied under isothermal conditions, using a specific HPLC assay to determine residual activity. Inactivation of the blood enzyme preparation followed first order kinetics, with z-values in phosphate buffer (pH 6·7) and skimmed milk of 6·5 and 7·6 °C, respectively, the enzyme being far more stable in the latter environment. Inactivation kinetics of the enzyme purified from milk were more complex, and could be best approximated by a double exponential model. Again, stability was higher in milk than in buffer. The double exponential model may indicate differing heat stabilities of isoforms of the enzyme, or stabilization of the enzyme by some milk constituent. It is clear that the enzyme can survive, at least partially, processes such as heating at 55 °C for 30 min during manufacture of high-cook cheese varieties (45% survival), and HTST pasteurization (8% survival), and thus may contribute to proteolysis in a range of dairy products.

We recently reported the identification of a peptide from yoghurts with promising potential for intestinal health: the sequence (94-123) of bovine β-casein. This peptide, composed of 30 amino acid residues, maintains intestinal homoeostasis through production of the secreted mucin MUC2 and of the transmembrane-associated mucin MUC4. Our study aimed to search for the minimal sequence responsible for the biological activity of β-CN(94-123) by using several strategies based on (i) known bioactive peptides encrypted in β-CN(94-123), (ii) in silico prediction of peptides reactivity and (iii) digestion of β-CN(94-123) by enzymes of intestinal brush border membranes. The revealed sequences were tested in vitro on human intestinal mucus-producing HT29-MTX cells. We demonstrated that β-CN(108-113) (an ACE-inhibitory peptide) and β-CN(114-119) (an opioid peptide named neocasomorphin-6) up-regulated MUC4 expression whereas levels of the secreted mucins MUC2 and MUC5AC remained unchanged. The digestion of β-CN(94-123) by intestinal enzymes showed that the peptides β-CN(94-108) and β-CN(117-123) were present throughout 1·5 to 3 h of digestion, respectively. These two peptides raised MUC5AC expression while β-CN(117-123) also induced a decrease in the level of MUC2 mRNA and protein. In addition, this inhibitory effect was reproduced in airway epithelial cells. In conclusion, β-CN(94-123) is a multifunctional molecule but only the sequence of 30 amino acids has a stimulating effect on the production of MUC2, a crucial factor of intestinal protection.

Dialysing milk against phosphate-free sera showed that the transition in the ethanol (EtOH) stability/pH profile was associated with the soluble phosphate component of the milk serum. Sigmoidal behaviour similar to that of milk was reproduced when the EtOH stability of artificial mixtures of casein, Ca and phosphate was measured as a function of pH. A mechanism for the s coagulation of skim-milk is discussed.

The yield and composition of milk from Friesian cows grazing either perennial ryegrass (Lolium perenne) (G, ten cows) or white clover (Trifolium repens) (C, nine cows) were evaluated between d 21 and 129 post partum. The two forages, of similar digestible energy content, were the sole source of nutrients and were offered ad lib. (exp. 1). Digestion and flow at the duodenum were measured on 13 occasions in early lactation with comparable cows fitted with rumen and duodenal cannulae and grazing similar forages (exp. 2). The gross milk yield (22·2, G; 25·0, C, kg/d P < 0·05) and the yield of protein (0·66, G; 0·77, C, kg/d, P < 0·01) were higher, but the protein content was similar and the fat content lower for cows fed C compared with G. Cows fed G were heavier at the beginning of the experiment and lost weight more rapidly than cows fed C. Milk energy output, adjusted for tissue energy gain or loss, was 83·9 for cows fed C compared with 71·8 MJ/d for cows fed G (P < 0·001), during the period of tissue energy repletion (weeks 11–18). From week 18 to the end of lactation all cows from exp. 1 were fed silage ad lib. and 502 kg dry matter of concentrates. The total (305 d) difference in lactation response to grazing C compared with G was 931 1 (5657 1, C; 4726 1, G); this was a direct response during the experiment of 301 1 and a residual response of 630 1. In exp. 2, more organic matter (6·47, G; 8·01, C, kg/ d, P < 0·001), and more non-ammonia N (433, G; 575, C, g/d, P < 0·001) entered the duodenum of cows grazing C compared with G.