Microfiltration (MF) of milk with a ceramic membrane (0·1 μm mean pore diam.) for the separation of casein micelles from soluble proteins was studied. Experiments were performed at constant flux density (J=65 or 75 l h−1 m−2) and wall shear stress (τw=100 or 110 Pa) with milks containing particles and solutes with different sizes and charges, produced by physicochemical change (heat and mechanical treatment, pH, ionic strength, addition of ions). Membrane separation performance was limited by the build up of a cake with characteristics that depended on the size of particles and soluble proteins. Best performance (higher permeability and whey protein transmission) was obtained with milk containing fat on the one hand and calcium phosphate on the other. An optimal value of the particle size was found, close to 0·5–3·0 μm; above this separation performance decreased. In addition, the present study confirmed that the transfer of charged solutes is the consequence of both size and ionic exclusion. Better performance was achieved with higher ionic strength (1 M).

Streptococcus (Str.) agalactiae is a contagious mastitis bacterium, often associated with cases of subclinical mastitis. Different mastitis bacteria have been evaluated previously from a diagnostic point of view, but there is a lack of knowledge concerning their effect on milk composition. Protein composition is important in achieving optimal yield and texture when milk is processed to fermented products, such as cheese and yoghurt, and is thus of great economic value. The aim of this in vitro study was to evaluate protein degradation mainly caused by exogenous proteases originating from naturally occurring Str. agalactiae. The samples were incubated at 37°C to imitate degradation caused by the bacteria in the udder. Protein degradation caused by different strains of Str. agalactiae was also investigated. Protein degradation was observed to occur when Str. agalactiae was added to milk, but there were variations between strains of the bacteria. Caseins, the most economically important proteins in milk, were degraded up to 75% in milk inoculated with Str. agalactiae in relation to sterile ultra-high temperature (UHT) milk, used as control milk. The major whey proteins, α-lactalbumin and β-lactoglobulin, were degraded up to 21% in relation to the sterile control milk. These results suggest that different mastitis bacteria but also different strains of mastitis bacteria should be evaluated from a milk quality perspective to gain knowledge about their ability to degrade the economically important proteins in milk.

Calf rennet, bovine pepsin, and porcine pepsin were used to produce cheese curd, using the same milk and lactic culture for each. Specimens were prepared for scanning electron microscope examination by a modified critical-point drying technique.

From examination of the micrographs, the curd made with bovine and porcine pepsin were similar in structure and in orientation of the coagulated protein, whereas the curd produced with rennet was different, having a more compact and organized structure.

Using gel electrophoresis a genetic polymorphism of αs2-casein (Cn) was discovered in individual milk samples from 2 bovine breeds of the eastern part of France (Vosgienne and Montbéliarde). The 3 observed phenotypes (Plate 1) are determined by 2 co-dominant alleles at an autosomal locus. The αs2-Cn A variant was the only one known up to now in European breeds (reference variant) and ±s2-Cn D is a new variant, whose bands overlap the β-casein A band at pH 8.6, and migrate faster than αs2-Cn A at pH 3.0.

The sequence of the polypeptide chain αs2-Cn D differs from that of αs2-Cn A by the deletion of a very acidic nonapeptide, which includes a cluster of 3 phosphoseryl residues. Due to the characteristics of the reference sequence, this deletion cannot be exactly located but it involves residues 50–58, or 51–59, or 52–60.

A genetic analysis shows that locus αs2-Cn is closely linked to the cluster αsl-Cn–β-Cn-K-Cn. The 4 casein species are thus synthesized by 4 closely linked loci.

The marked precipitation of Ca phosphate found to occur at ~ pH 6·8 when milk is heated to high temperatures may account for the minimum in the heat coagulation time (HCT)–pH curve at ~ pH 6·8. Dialysis of milk against water for about 3 h converted a normal type A milk to one with type B heat stability characteristics by reducing stability in the region of the HCT maximum while increasing stability in the region of the minimum. Reduction of the concentration of urea, lactose, Na or chloride did not cause these changes and gross micelle structure appeared to be intact following short dialysis as indicated by turbidity and sedimentability. Dilution of milk with water increased stability at the minimum without significantly affecting stability at the maximum. Pre-heating at 80°C for 10 min precluded the effect of dilution but not of dialysis.

The composition of ewe's milk during the first 4 days of lactation and on the 100th day of lactation was investigated. The total fat content was highest (17· 9%) on the day of parturition but decreased rapidly to reach a level on the 2nd day after parturition that was similar to that observed on the 100th day of lactation (9·9 %).

The concentration of octadecenoic acid, which was the major fatty acid of ewe's milk, was very much higher in early lactation than in late lactation. As the concentration of octadecenoic acid decreased the concentration of the shorter chain fatty acids (6:0−14:0) increased. The major octadecenoic acid was the cis-9 isomer. However, the proportion of the trans-11 isomer increased from 5·5 % of the total octadecenoic acid concentration in early lactation to 11·9 % in late lactation. Although linoleic acid remained a minor component of the fatty acids of the milk during lactation, its concentration increased from less than 1 % during early lactation to 1·4 % by the 100th day of lactation.

The high nutritional value of whey makes it an interesting substrate for the development of fermented foods. The aim of this work was to evaluate the growth and proteolytic activity of sixty-four strains of lactic acid bacteria in whey to further formulate a starter culture for the development of fermented whey-based beverages. Fermentations were performed at 37°C for 24 h in 10 and 16% (w/v) reconstituted whey powder. Cultivable populations, pH, and proteolytic activity (o-phthaldialdehyde test) were determined at 6 and 24 h incubation. Hydrolysis of whey proteins was analysed by Tricine SDS-PAGE. A principal component analysis (PCA) was applied to evaluate the behaviour of strains. Forty-six percent of the strains grew between 1 and 2 Δlog CFU/ml while 19% grew less than 0·9 Δlog CFU/ml in both reconstituted whey solutions. Regarding the proteolytic activity, most of the lactobacilli released amino acids and small peptides during the first 6 h incubation while streptococci consumed the amino acids initially present in whey to sustain growth. Whey proteins were degraded by the studied strains although to different extents. Special attention was paid to the main allergenic whey protein, β-lactoglobulin, which was degraded the most by Lactobacillus acidophilus CRL 636 and Lb. delbrueckii subsp. bulgaricus CRL 656. The strain variability observed and the PCA applied in this study allowed selecting appropriate strains able to improve the nutritional characteristics (through amino group release and protein degradation) and storage (decrease in pH) of whey.

Storage of aseptically packed ultra-high-temperature (UHT) milk has been shown to be accompanied by pronounced changes in the molecular weight distribution of the pH 4·6 insoluble casein. These changes were both time-dependent and temperature-dependent, proceeding much more rapidly at 37 °C than at 30 °C, but even at 4 °C the changes were considerable. The proportions of high molecular weight material present before and after storage have been studied by gel filtration in dissociating solvents using Sephadex G-200. Measurements have also been made on casein material isolated from in-bottle sterilized milks and canned evaporated milk for comparison. The results of gel filtration have been compared with sedimentation coefficients recorded by ultracentrifugation and with changes in the content of amino groups titratable with trinitrobenzene-sulphonic acid. The results are compatible with the suggestion that the Maillard reaction occurred at ambient temperatures, and over a period of several months led to browning and sediment formation due to covalent cross-linking of polypeptide chains. The implications of this are discussed with reference to spoilage of UHT milk on storage and the phenomenon of gelation.

1. The literature on the soluble protein fraction of milk has been reviewed to show the difficulties that are encountered in attempting to decide whether the fraction consists, as is usually supposed, of lactalbumin and lactoglobulin only, or whether it consists partly of secondary proteins of a proteose-peptone nature.

2. It has been shown that on boiling the casein-free filtrate of milk, maximum coagulation of albumin and globulin occurs at a pH. of 4–75–4–80. At this pS. prolonged boiling does not cause hydrolysis, and the amount of albumin and globulin N coagulated represents about 70 per cent of the total soluble protein N of milk.

3.By precipitation of the casein-free nitrate of milk with various con- centrations of trichloracetic acid, a partition of the soluble proteins has been effected which strongly suggests the presence of proteose-peptone substances to an extent in agreement with the results of heat coagulation.

4. The maximum amount of albumin and globulin rendered coagulable by heating milk itself has been determined by precipitating denatured albumin and globulin along with casein at pH. 4–7. This maximum represented an average of 76 per cent of the total soluble protein N in a series of normal milk samples, and reasons have been given for considering this maximum as the total of true albumin and globulin present.

5. The conclusion has been reached that the soluble protein fraction of normal fresh milk is composed of approximately 76 per cent albumin and globulin, and 24 per cent proteose-peptone substances.

1. Despite the presence of appreciable quantities of steam volatile fatty acids as glycerides in butterfat, no short-chain fatty acids with odd carbon number have been detected by gas-liquid chromatography of the acids.

2. Mild oxidation of butterfat for short periods of time produces steam volatile fatty acids with odd carbon number. A large proportion of these acids was formic, with smaller proportions of propionic, valeric and nonanoic acids.

3. The relative ease with which short-chain fatty acids are produced on oxidation of fats, points to the danger of contaminating naturally occurring fatty acids with extraneous acids.

4. A total analysis of the fatty acids of New Zealand butterfat by gas-liquid chromatography compared well with similar analyses carried out by previous workers by means of esterfractionation analysis.

It has been shown that the inhibition caused by heat treatment, of the primary phase of rennin action on casein micelles, is dependent on the presence of β-lactoglobulin. The degree of inhibition increased with increasing amounts of added β-lactoglobulin for both heated casein micelles and heated skim-milk to a constant value. The results are fully consistent with the hypothesis that the inhibition is caused by complex formation between β-lactoglobulin and κ-casein when milk is heated.

Two experiments were carried out, Expt. 1 with twelve cows in a 4×4 Latin square and Expt. 2 with twenty-six cows in two groups which spent 11 weeks on the experimental rations. In both experiments hay and silage were fed ad lib. In Expt. 1 four levels of concentrate feeding were offered, 1¼, 2½, 3¾ and 5 lb/gal, and in Expt. 2 two levels, 1¼and 5 lb/gal. The levels of feeding as a percentage of Woodman's standards for starch equivalent (S.E.) ranged from 82 to 125% in Expt. 1 and from 83 to 116% in Expt. 2; for digestible crude protein (D.C.P.) the corresponding figures were 70–100% and 105–107%. When concentrate consumption increased by 1 lb dry matter the consumption of bulk feeds was reduced by 0·18–0·22 lb dry matter but the total fibre intake remained constant. Milk yield showed small but significant responses to level of feeding. Average responses per 1 lb S.E. were 0·77 lb milk in Expt. 1 and 0·61 lb milk in Expt. 2. Total lactation yields of the cows in Expt. 2 were unaffected by the experimental treatments. The production S.E. fed per gallon of milk ranged from 1·71 to 3·72 lb in Expt. 1 and from 1·92 to 3·27 lb in Expt 2. Production D.C.P. ranged from 0·37 to 0·63 lb and from 0·67 to 0·70 lb, respectively.

High levels of feeding increased the S.N.F. and protein contents of the milk but did not affect other constituents. The responses in S.N.F. were lower than in some other experiments and some cows showed no response. The results are discussed with reference to the experimental methods and also with reference to the yield responses compared with published data, and to the practical importance of the high production obtained with low usage of concentrate feeds.

In the context of identifying intrinsic time temperature integrators (TTIs) for evaluating heat processing of milk, the extent to which milk fat content has an effect on alkaline phosphatase (ALP) and lactoperoxidase (Lpo) inactivation and on β-lactoglobulin (β-lg) denaturation kinetics was studied. Inactivation and denaturation kinetics were analysed in whole, semi-skimmed and skimmed milk. In previous experiments (isothermal and non-isothermal heating conditions), heat inactivation of ALP and Lpo and heat denaturation of β-lg were found to follow first order kinetics. This allowed experimental design to be simplified. Data analysis was performed by non-linear regression and results were evaluated by construction of joint confidence regions. The possible effect of milk fat was illustrated by temperature time tolerance (TTT-) diagrams. Although initial ALP activity was lower in skimmed milk compared with semi-skimmed or whole milk, kinetics were comparable and fat content did not seem to substantially affect the ALP test result for pasteurized milk. Unlike ALP, Lpo inactivation and β-lg denaturation kinetics differed significantly in milk with different fat content. Differences between Lpo inactivation kinetics were relatively small and acceptable in the context of quantifying the process impact. Denaturation of β-lg, on the other hand, seemed to be enhanced at higher milk fat content (>72 °C).

Nutritional deficiency is commonly associated with impaired immune response and the relation between infection and malnutrition is synergic. Probiotics, especially lactic acid bacteria are immunomodulatory. The aim was to determine whether optimal doses of Lactobacillus casei and yogurt, used as adjuvants in a re-nutrition diet in a non-severe malnutrition experimental model, protect against Salmonella typhimurium and Escherichia coli. Groups of malnourished mice were used, which were re-nourished with milk for 7 or 14 d. After that, both groups of mice received the optimal doses of Lb. casei and yogurt supplements. We measured IgA+ and IgG+-B cells and phenotypic markers of T lymphocytes; CD3+, CD4+ and CD8+ cells. We also determined αβ and γδ T cell receptor (TCR). The ability to protect against Sal. typhimurium and Esch. coli infections and specific S-IgA were assessed. Probiotics complemented the effects of the re-nutrition diet, by stimulating recuperation of the activity of immune cells that improved protection against infections.

In this work, the genetic variation of milk FA was investigated in three different bovine breeds, the Jersey, the Piedmontese and the Valdostana, and at different lactation stages. All animals were genotyped for 21 Single Nucleotide Polymorphisms located within nine candidate genes involved in lipid synthesis: diacylglycerol acyltransferase 1 and 2 (DGAT1, 2); stearoyl-CoA desaturase (SCD); growth hormone receptor (GHR); fatty acid synthase (FASN); acyl-CoA dehydrogenase (ACAD); fatty acid binding protein (FABP4); lipoprotein lipase (LPL); and leptin gene (LEP). The highest milk-fat Jersey breed also showed the highest content of saturated FA. Throughout lactation, the breeds showed a similar variation in the FA, with a decrease in the short-chain, this was accompanied by a general increase in the long chain FA at the end of lactation. The increase in long chain saturated FA was particularly evident in the case of the Jersey. The effect of SCD gene on the C14 desaturation index was confirmed; the DGAT1 gene was polymorphic only in the Jersey breed, but its effect was confirmed only on milk fat content; three further potential candidate genes were identified: first, the FABP4 gene, which was found to influence medium and long chain FA in all the breeds, but not the desaturation indices; second, the FASN gene, which was found to influence the amount of PUFA in the Piedmontese and the Valdostana, and third, the LPL gene, which was found to affect fat content in the Piedmontese.

Thirty Holstein cows in mid-lactation (158±20 DIM) were given a total mixed ration based on grass silage, maize silage and rolled barley. After a preliminary period of 1 week, this diet was supplemented with nothing (control), unprotected fish oil (3.7% of dry matter, DM), or two levels of glutaraldehyde-protected microcapsules of fish oil (1.5% and 3.0% of DM, respectively). Unprotected and protected supplements contained, respectively, 74% and 58% of DM as lipids. Cows given the unprotected supplement reduced their feed intake by >25%. Consequently, these cows lost body weight and produced less milk. DM intake, body weight, and milk yield were unaffected by protected fish oil. Fish oil reduced both milk fat and protein percentages, and decreased the proportion of short-chain fatty acids, stearic, and oleic acids in milk fat. Milk trans C18[ratio ]1 fatty acids increased in cows given both unprotected and protected fish oil. Milk fat content of very-long-chain n3 polyunsaturated fatty acids, including C20[ratio ]5 and C22[ratio ]6, increased with fish oil in the diet. Accordingly, the peroxide index increased and a taste panel was able to detect unusual taste in milk from cows consuming the higher level of protected fish oil and disliked the milk from cows given unprotected fish oil. In conclusion, when lactating cows consumed fish oil, milk concentration of long-chain n3 fatty acids increased and mammary de novo synthesis of fatty acids decreased, but milk yield and milk protein content were reduced, and the milk was more susceptible to oxidation and its taste was adversely affected.

1. Using the capillary technique previously described, examination has been made of various factors in relation to the reactivation of raw milk phosphatase. Of these, ageing of the raw milk was found to affect considerably the level of reactivation, this increasing as the bacteriological quality of the milk deteriorated.

2. It has been found that absence of air and the presence of reducing conditions in the raw milk increases the reactivation obtained.

3. The influence of reducing conditions on the reactivation of a bacterial phosphatase has been demonstrated.

Phytanic acid, 3,7,11,15-tetramethylhexadecanoic acid, which hitherto had been isolated and identified from several natural sources including butterfat, ox perinephric fat and cow plasma, has now been found present in small amounts (2·9%) in the total fatty acids extracted from the rumen bacteria of a fistulated dairy cow fed a diet of clover-grass hay. This C20 multibranched fatty acid was not detected in the dietary clover-grass hay, and it is considered to have been derived from phytol by enzymic activity of the rumen bacteria.

In the present work, 67 strains of Lactobacillus helveticus isolated from whey starter cultures and cheeses were identified and grouped by genotypic and phenotypic methods. Strains were identified by sugar fermentation pattern, by cell-wall protein profile, and by probe hybridisation. Phenotypic diversity was evaluated by a chemometric model taking into account biochemical characteristics (i.e. acidifying and peptidase activities) of technological interest. Genotypic diversity was evidenced by RAPD-PCR, which provided strain-specific patterns and revealed the occurrence of different strains. The RAPD-PCR profiles were clustered according to their similarities; the groups obtained, together with the cell-wall protein profiling and the chemometric information, could be sometimes correlated with the type of cheese and/or dairy niches used as sources of strains. A computerised analysis of genotypic and phenotypic information could be successfully applied for rapid and reliable differentiation and characterisation of Lb. helveticus isolates occurring in different dairy products.