A sample of milk fat was fractionated into high, medium and low molecular weight triglycerides by silicic acid column chromatography. Each fraction was further separated by silver ion adsorption thin-layer chromatography into triglyceride classes which were subjected to stereospecific analysis. Trans-monoene fatty acids were incorporated into triglycerides in the same manner as their cis-isomer. The specific positional distribution for fatty acids in intact milk fat triglycerides was not always maintained in the molecular weight fractions or in the various classes of unsaturation. The significance of these findings is discussed in relation to biosynthetic mechanisms for milk fat synthesis.

Some strains of commercial cheese starters were obtained in higher yield after batch culture in whey-based media supplemented with soy peptones than in those supplemented with papain digested skim-milk. The soy peptones contained a greater proportion of small peptides than did the skim-milk digest. Also the average size of peptides was lower (3·4–3·9 residues) in soy preparations than in the milk digest (6·8). Small peptides isolated from the soy peptones were utilized by growing starters more completely than the equivalent peptides isolated from the papain digested milk. These observations may account for the difference in cell yields with soy and milk-digest peptones.

β-Casein is highly resistant to proteolysis in Cheddar cheese. A decrease in NaCl concentration reduced its resistance, but even in the absence of salt the amount of proteolysis of β-casein was slight. Proteolysis in Cheddar cheese increased when the moisture levels were raised by adding water. The relative susceptibility of β-casein to proteolysis by rennin was reduced considerably when the concentration of a sodium caseinate solution was raised from 10 to 20%. Sequestering the Ca2+ by means of EDTA had no significant effect on proteolysis of β-casein. It would appear that the resistance of β-casein to proteolysis is due to the substrate rather than the enzyme and it is suggested that the reduced relative susceptibility to proteolysis is due to some concentration-dependent physical change in the casein molecule which renders the β-casein inaccessible. The salt concentration would also appear to influence this change.

Cheddar-cheese flavour is largely independent of rennet concentration and it is possible to manufacture cheese of satisfactory quality using half-normal rennet levels.

Twelve multiparous British Friesian cows in early (40±23 d in milk; n=6) or late (216±17 d in milk; n=6) lactation were used to study the effects of milking frequency on yield, udder volume and milk storage within the udder. After a 2 week control period of twice daily milking, diagonally opposed udder halves within a cow were milked once or twice daily for 3 weeks. Milk yield was 28–38% lower from the halves that were milked once daily than from halves that were milked twice daily. The loss of milk yield, expressed as a decrease in the relative milk yield quotient (an index that accounts for pretreatment differences), was greater for cows in early than in late lactation (0·59 v. 0·68). Empty udder-half volume was not decreased by once daily milking, suggesting that no cell loss occurred. Instead, once daily milking reduced the secretion efficiency (units of milk per unit of empty udder-half volume) by 46 and 27% respectively in early and late lactation; thus, at least part of the loss was due to reduced metabolic activity of the mammary epithelium. There were positive correlations between the relative milk yield quotient and the proportion (r=0·804) or volume (r=0·644) of cisternal milk in the glands that were milked once daily. These results confirm that, during extended milking intervals, milk loss was smallest for cows that stored a larger proportion of milk in the gland cistern.

The effect of freeze-drying on viability and probiotic properties of a microbial mixture containing selected bacterial and yeast strains isolated from kefir grains (Lactobacillus kefir, Lactobacillus plantarum, Lactococcus lactis, Saccharomyces cerevisiae and Kluyveromyces marxianus) was studied. The microorganisms were selected according to their potentially probiotic properties in vitro already reported. Two types of formulations were performed, a microbial mixture (MM) suspended in milk and a milk product fermented with MM (FMM). To test the effect of storage on viability of microorganisms, MM and FMM were freeze-dried and maintained at 4°C for six months. After 180 days of storage at 4°C, freeze-dried MM showed better survival rates for each strain than freeze-dried FMM. The addition of sugars (trehalose or sucrose) did not improve the survival rates of any of the microorganisms after freeze-drying. Freeze-drying did not affect the capacity of MM to inhibit growth of Shigella sonnei in vitro, since the co-incubation of this pathogen with freeze-dried MM produced a decrease of 2 log in Shigella viability. The safety of freeze-dried MM was tested in mice and non-translocation of microorganisms to liver or spleen was observed in BALB/c mice feed ad libitum during 7 or 20 days. To our knowledge, this is the first report about the effect of freeze-drying on viability, in vitro probiotic properties and microbial translocation of a mixture containing different strains of both bacteria and yeasts isolated from kefir.

The aim of the study was to identify the species of Enterobacteriaceae present in Montasio cheese and to assess their potential to produce biogenic amines. Plate count methods and an Enterobacterial Repetitive Intergenic Consensus Polymerase Chain Reaction (ERIC-PCR) approach, combined with 16S rDNA sequencing, were used to investigate the Enterobacteriaceae community present during the cheesemaking and ripening of 6 batches of Montasio cheese. Additionally, the potential decarboxylation abilities of selected bacterial isolates were qualitatively and quantitatively assessed against tyrosine, histidine, ornithine and lysine. The most predominant species detected during cheese manufacturing and ripening were Enterobacter cloacae, Escherichia coli and Hafnia alvei. The non-limiting physico-chemical conditions (pH, NaCl% and aw) during ripening were probably the cause of the presence of detectable levels of Enterobacteriaceae up to 120 d of ripening. The HPLC test showed that cadaverine and putrescine were the amines produced in higher amounts by almost all isolates, indicating that the presence of these amines in cheese can be linked to the presence of high counts of Enterobacteriaceae. 44 isolates produced low amounts of histamine (<300 ppm), and four isolates produced more than 1000 ppm of this amine. Only 9 isolates, belonging to the species Citrobacter freundii, Esch. coli and Raoultella ornithinolytica, appeared to produce tyramine. These data provided new information regarding the decarboxylase activity of some Enterobacteriaceae species, including Pantoea agglomerans, Esch. fergusonii and R. ornithinolytica.

1. A study has been made of the interrelationships between persistency and maximum yield as components of the lactation curve, and of the importance of environment and heredity in determining the shape of the lactation curve of Ayrshire cows.

2. Persistency was defined as the linear constant of the exponential curve expressed as a percentage, maximum yield as the highest 30-day yield as calculated from the records, and total yield as the yield of milk from 15 days to 8½ months after calving.

3. The study was based on milk records computed by the official method of the Scottish Milk Records Association. The data used in much of the work was obtained from five herds of Ayrshire cows and involved 2392 lactations during the period 1920–39.

4. In an exploratory test involving 100 lactations it was found that the exponential curve fitted ninety-five of the lactation curves and that the fit was improved in forty-eight of these ninety-five curves by using the parabolic exponential curve. Five of the lactations were too erratic to be fitted by any simple mathematical curve.

Micelles reconstituted from urea-treated milk by exhaustive dialysis against bulk milk were similar to native micelles with respect to colloidal phosphate: casein ratio, ethanol stability, heat stability and susceptibility to first-stage rennin action. Reconstituted micelles were considerably smaller than native micelles as indicated by turbidity, sedimentation and viscosity, had shorter second-stage rennet coagulation times, were unstable to [Ca2+] > 20 mM and had reduced base-binding capacity. It is suggested that the induced Ca sensitivity is due to unfavourable alterations in the micellar κ-casein coat arising from the decrease in average micelle size and can be offset by increasing the κ-casein complement of the system or by increasing the degree of aggregation by slowly raising the [Ca2+] level.

A method has been developed for quantitative determination of para-κ-casein, involving spectrophotometric scanning of stained protein bands following polyacrylamide gel electrophoresis. The rate of hydrolysis of κ-casein in skim-milk at pH 6·6 and 30 °C was compared with that in EDTA-treated skim-milk under the same conditions. This showed that at the visually observed clotting time, at least 90% of the total κ-casein in milk had been hydrolysed. The time course of the reaction was consistent with all the κ-casein molecules being hydrolysed with the same efficiency. The results strongly suggest that essentially all of the κ-casein in milk is equally accessible to rennet action. This is consistent with the casein micelle being porous, or having all the κ-casein on the surface.

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.

Due to increasing public concern regarding separation of the dairy cow and calf within the first days after birth, alternative systems, where cows and calves stay in contact for an extended period, are receiving increasing interest from a broad array of researchers and other stakeholders. With more research in the area, there is a risk of inconsistencies emerging in the use of terminology. To create a better consensus in further discussions, the aim of this Research Reflection is to provide definitions and propose a common terminology for cow-calf contact in dairy production. We also suggest definitions for various systems allowing cow-calf contact and describe the distinct phases of cow-calf contact systems.

Although there has been little study of the origin of intramammary infection (IMI) in goats, a common view is that most bacterial infection in goats occurs during milking. In the present study, the dynamics of occurrence of udder infection during and between lactations in three Anglo-Nubian goat farms in Israel was monitored. Coagulase-negative staphylococci were the predominant bacteria in the IMIs. We found that about 15% of the yearling does were already infected with bacteria when they joined the flock, whereas about 8% of the goats that dried-off returned with new IMIs. Moreover, virtually none of the goats acquired infection during lactation. Thus, our study showed that the aetiology of IMI in goats is very similar to that in dairy cows. A preventive treatment during the dry period should, therefore, be considered as an effective means of reducing the current rate of bacterial infections in goats.

Indigenous L-lactate dehydrogenase (LDH) in milk originates mainly from somatic cells, leucocytes and invading microorganisms. Its activity may be used for detection of mastitis. However, existing methods to measure LDH activity in milk both need pretreatment of the samples and still suffer from methodological problems. The present paper describes a fast, reliable method for determination of LDH activity, suitable for milk samples. The method is based on fluorometric determination of enzyme kinetics when L-lactate is converted to pyruvate. The assay uses raw milk without pretreatment and the method is easily adjustable to large-scale analyses on micro assay plates. Detection is based on (straight line) linear response within 4–7 min of initiation of the reaction. A substrate concentration of 35 mM in the reaction mixture was considered to be optimal for the assay. Intra plate assay precision was approx. 6% (CV) and the inter plate precision approx. 10%. Known inhibitors of LDH activity (oxidative direction), i.e., oxalic acid, oxamate, and pyruvate, were tested in different concentrations in order to verify the specificity of the response. The detailed kinetics of samples analysed indicated that the isoenzyme composition may have differed between milk samples, and that this composition may have been altered in high activity samples.

Plant oils in the diet are known to alter milk fat composition owing to changes in the supply of fatty acid precursors and/or activity of lipogenic enzymes in the mammary gland. Thirteen mid-lactating Alpine goats were used in a 3×3 Latin square design with 28-d periods to evaluate possible mechanisms regulating milk fat synthesis and fatty acid composition on grass hay-based diets containing none (H) or 55 g/kg diet dry matter of sunflower-seed oil (HSO) or linseed oil (HLO). Inclusion of oils in the diet had no effect on milk yield but enhanced (P<0·05) milk fat secretion. Compared with the control, HLO and HSO decreased (P<0·05) C10–C16 secretion and increased (P<0·05) C18 output in milk, responses that were accompanied by reductions in milk fat cis-9 14:1/14:0, cis-9 18:1/18:0 and cis-9, trans-11 18:2/cis-9 18:1 concentration ratios. Plant oil supplements decreased (P<0·05) mammary stearoyl-CoA desaturase (SCD) activity but had no effect on SCD mRNA. Treatments had no effect on glucose-6-phosphate dehydrogenase, malic enzyme and glycerol-3-phosphate dehydrogenase activity, or mRNA abundance and/or activity of lipoprotein lipase, acetyl-CoA carboxylase and fatty acid synthase in mammary, hepatic or adipose tissue. The results provided little support for milk fatty acid secretion responses to HLO and HSO being mediated via changes in mammary, hepatic or adipose mRNA abundance or in the activity of key lipogenic enzymes. In conclusion, plant oils in the diet enhance milk fat synthesis, alter milk fatty acid composition and specifically inhibit mammary SCD activity in the goat. Furthermore, the results suggest that the regulation of mammary lipogenesis in response to plant oils appears related to factors other than altered mammary gene expression or potential lipogenic enzyme activity.

A method is described for determining H2S, methanethiol and dimethyl sulphide in Cheddar-cheese headspace. Cheeses ranging in age from 2 to 12 months were analysed using a gas chromatograph equipped with a photometric detector. These cheeses were presented to a trained flavour panel for the assessment of quality and intensity of Cheddar cheese flavour.

An attempt is made to correlate the concentration of sulphur compounds in the headspace with the average flavour scores. The results suggest that the flavour intensity of the cheese is related to the concentration of methanethiol in the headspace.

To improve acid clotting properties, enzymic dephosphorylation of caseins with calf intestinal alkaline phosphatase (CAP) or potato acid phosphatase (PAP) was investigated. Greater dephosphorylation was achieved using αs1- or β-casein as substrates, compared to whole casein or skim milk. Electrophoresis of PAP-modified caseins revealed bands with lower mobility and a multibanded pattern in the β-casein region which was similar to that of human β-casein. On the other hand, CAP modification produced electrophoretic bands having lower mobility of the β-casein component, but with higher mobility in the αs1-casein component as well as increased net negative charge in the CAP-casein. PAP-casein formed a fine dispersion upon acidification to pH 4. with a microstructure similar to that of acidified human casein. Greater initial rates of hydrolysis by pepsin at pH 4 were observed for both CAP- and PAP-modified caseins, compared to bovine and human caseins. The rate and extent of hydrolysis remained high for CAP-casein but tended to level off with PAP-casein during sequential digestion with pepsin and pancreatin. There may be advantages in the use of partial dephosphorylation to improve acid clotting and digestibility properties of bovine casein for infant feeding.

In addition to a control diet, lactating cows were offered saturated fatty acid mixtures in three forms, free acids, free triglycerides and protected triglycerides, i.e. triglyceride encapsulated within a protein matrix which was cross linked by exposure to formaldehyde. Relative to the control diet, all three supplements increased milk yield. However, only the free fatty acids gave rise to increased yields of the three major milk components. The free fat and the protected fat caused significant increases only in the lactose yield. The different effects of the supplements on the yield of milk fat are suggested to be due to the types of long chain acid reaching the mammary gland rather than to any change in rumen activity. Changes in the concentrations of the soluble multivalent ionic constituents of the milks were consistent with this conclusion.

Samples of commercially processed ultra-high-temperature (UHT) milk were stored at 4, 20, 30 and 37°C for up to 2 years or until gelation occurred.

The stability of the proteins to ethanol, calcium ions and rennet decreased with time of storage. However, preliminary autoclaving of the UHT milk induced a high degree of stability.

The extent of protein decomposition that had occurred in the UHT milk samples depended on the time and temperature of storage. There was negligible decomposition when the samples had been autoclaved before storage at 4 and 20°C. Storage at 37°C led to significant decomposition.

UHT milk samples gelled after being stored for 13 months at 4, 20 and 30°C, but not at 37°C. The autoclaved milk was still fluid after being stored for 2 years at these temperatures.

The time of onset of gelation did not depend on the degree of protein breakdown, and it seemed therefore that proteolysis was not the primary cause of gelation on storage.

It was concluded that the proteins in UHT milk underwent several changes on storage that were apparently independent of each other and led ultimately to coagulation of the milk. These changes included proteolysis, and a progressive loss of stability under conditions that favoured aggregation of the casein micelles.

Hispánico cheese, a semi-hard Spanish variety, was manufactured from a mixture of pasteurized cows' and ewes' milks (4[ratio ]1) using a commercial mesophilic LD-type starter comprising Lactococcus lactis subsp. cremoris, Lc. lactis subsp. lactis, Lc. lactis subsp. lactis var diacetylactis and Leuconostoc mesenteroides subsp. cremoris. Varying amounts (0–1·0 g/kg) of an Enterococcus faecalis INIA 4 culture in milk were added as a bacteriocin-producing adjunct. Differences in pH between cheeses manufactured with and without the bacteriocin producer did not exceed 0·11 pH units. Starter lactococci lost viability more rapidly in cheeses made with the bacteriocin producer, which reached counts of up to 6×107 cfu/g during ripening. Aminopeptidase activity in 1-d-old cheese made from milk inoculated with 1·0 g bacteriocin-producing culture/kg was twice that in control cheese. Degrees of overall proteolysis and levels of total free amino acids in 45-d-old cheese made with 1·0 g bacteriocin-producing culture/kg were 1·80-fold and 2·17-fold those in control cheese of the same age. Inoculating milk with 1·0 g/kg bacteriocin-producing culture reduced the level of hydrophobic peptides in the resultant cheese, increased the concentrations of 3-methyl-1-butanal, diacetyl and acetoin, and resulted in the highest scores for flavour quality and flavour intensity throughout ripening.

Whey protein hydrolysates were generated at different total solids (TS) levels (50–300 g/l) using the commercially available proteolytic preparation Debitrase™ HYW20, while enzyme to substrate ratio, pH and temperature were maintained constant. Hydrolysis proceeded at a faster rate at lower TS reaching a degree of hydrolysis (DH) of 16·6% at 300 g TS/l, compared with a DH of 22·7% at 50 g TS/l after 6 h hydrolysis. The slower breakdown of intact whey proteins at high TS was quantified by gel-permeation HPLC. Reversed-phase (RP) HPLC of hydrolysate samples of equivalent DH (~15%) generated at different TS levels indicated that certain hydrophobic peptide peaks were present at higher levels in hydrolysates generated at low TS. Sensory evaluation showed that hydrolysates with equivalent DH values were significantly (P<0·0005) less bitter when generated at 300 g TS/l (mean bitterness score=25·4%) than hydrolysates generated at 50 g TS/l (mean bitterness score=39·9%). A specific hydrophobic peptide peak present at higher concentrations in hydrolysates generated at low TS was isolated and identified as β-lactoglobulin f(43–57), a fragment having the physical and chemical characteristics of a bitter peptide.