In this study, the chemical composition, proteolysis and in vitro angiotensin-converting enzyme-(ACE)-inhibitory and antioxidant activities of white cheeses made using probiotic adjunct cultures (Bifidobacterium bifidum DSMZ 20456 and Lactobacillus acidophilus DSMZ 20079) were investigated. The cheeses were ripened in a vacuum package or brine for 120 d at 4 °C. The cheese samples maintained the probiotic characteristics of the viable cells as >106 cfu/g even after ripening for 120 d. The proteolysis degrees in terms of water-soluble nitrogen/total nitrogen (WSN/TN), trichloroacetic acid-soluble nitrogen/total nitrogen (TCA-SN/TN) and phosphotungstic acid-soluble nitrogen/total nitrogen (PTA-SN/TN) values in the cheeses increased throughout the ripening. The highest levels of proteolysis were found in cheese made using Lb. acidophilus DSMZ 20079 and ripened in a vacuum package. ACE-inhibitory activity of the water soluble extracts (WSEs) of the cheeses increased significantly (P < 0·05) throughout the ripening (IC50 values 82·78–140·99 μg/ml). Use of Lb. acidophilus DSMZ 20079 and packaging under vacuum significantly increased the percentage of ACE inhibiting activity. WSEs had DPPH scavenging activity (the IC50 values were 2·41–5·39 mg/ml and the inhibition values were 5·10–10·38%), increasing up to 60 d ripening. In the present study, it was observed that Lb. acidophilus DSMZ 20079 was more effective than Bifido. bifidum DSMZ 20456 in terms of the cheese characteristics investigated.

Lactose could not be detected in the urine of non-lactating cows but was invariably found, though usually in low concentration, in the urine of lactating cows; the highest values were observed with cows of high lactation number. Towards the end of an extended milking interval of 39 h, the lactose concentration in the blood and the excretion of lactose in urine increased markedly, but on milking there was a rapid return to original values. Lactosuria was observed in pregnant cows from about 20 days before parturition, and at parturition there was a temporary, marked increase in the excretion of lactose in urine.

β-Lactoglobulin (β-lg) in aqueous solution under pressure showed a marked depolarization of intrinsic fluorescence assigned to a gradually increased rotational diffusion of tryptophyl moieties in pressure-unfolded states. The corresponding change in anisotropy provided a new and more accurate method for determining denaturation volume which, for β-lg in neutral aqueous solution with ionic strength 0·16 (NaCl) at 25 °C, was ΔV°=−73 (SE 3) ml mol−1, corresponding to half denaturation at 123 MPa. The pressure unfolding led to exposure of hydrophobic regions to the protein–water interface that could be probed by fluorescence intensity of a β-lg–1-anilinonaphthalene-8-sulphonic acid (ANS) complex with 1:1 stoichiometry, as determined by Job's method of continuous variation. The unfolding of β-lg impaired the binding capacity of the inner calyx, with a reduction in binding capacity of 50% at 50 MPa, as shown by decreasing cis- parinaric acid fluorescence, decreasing anisotropy and decreasing radiationless energy transfer from tryptophans to this probe with increasing pressure. The pressure-induced reversible exposure of hydrophobic groups to the protein–water interface may, at least partly, explain the initial aggregation reactions, evident from increased Rayleigh scattering from ∼50 MPa, prior to irreversible pressure-induced gel formation of β-lg. Using results from this and previous studies, we propose a three step pressure denaturation model for β-lg for neutral solution at ambient temperature, including an initial pressure-melted state (up to 50 MPa) with partial collapse of the inner calyx and solvent exposure of the free thiol group, followed by a reversible denaturation with exposure of hydrophobic regions (half denaturation at 123 MPa) and with irreversible denaturation with thiol–disulphide exchange becoming increasingly important at higher pressures. Effects of pressure on β-lg, as measured by fluorescence depolarization, were found for the reversible denaturation steps to be similar to the effects of chemical denaturants but different with respect to shift in ANS emission maxima.

The objective of this research was to determine the effect of exopolysaccharide (EPS) production by lactic acid bacteria on the microstructure and rheology of Karish cheese, a soft acid coagulated cheese made using skim milk. An EPS-producing strain of Streptococcus thermophilus, and its EPS non-producing genetic variant were used to make comparable batches of the cheese. EPS in cheese was visualized by cryo-SEM as a large, dense, filamentous mass. Cheese made with the EPS non-producing culture was characterized by a dense protein network with smaller pores compared to that prepared with the EPS-producing culture. High elastic and viscous moduli measured by dynamic rheology were observed for EPS negative cheese and was attributed to its dense protein network. Creep test experiments demonstrated that cheese prepared with the EPS non-producing strain was more rigid and recovered its deformation, while cheese made using the EPS producing culture was more deformable. These results indicate that EPS-producing cultures can improve the physical properties of Karish cheese by reducing undesirable rigidity.

The homogenization of milk and cream with a piston-type homogenizer has been studied. An examination has been made of the influences upon the mean fat globule diameters of changes in milk fat content, flow rate and homogenization temperature. The results are discussed in terms of the variations in the parameters q and P0 of the empirical equation d = (P0/P)q relating the globule diameter d to applied pressure P.

The effects of the addition of either 5 or 10% ‘oleic acid’ (78% pure) or 10% of a mixture of saturated fatty acids (64% palmitic acid, 31% stearic acid) to the dietary concentrate mixture on the yield and composition of the milk and milk fat and on the pattern of fermentation in the rumen were investigated in a feeding experiment with 8 cows in mid-lactation. The concentrate mixtures were given with a high-roughage diet that supplied 9·1 kg of hay/day.

The addition of 5% ‘oleic acid’ to the concentrate mixture resulted in increased yields of milk and solids-not-fat (SNF); the percentage of fat in the milk was decreased but the yield of milk fat was unaltered. The addition of 10% ‘oleic acid’ to the concentrate mixture decreased both the yield and percentage of fat in the milk. In contrast, the concentrate mixture containing 10% of the mixture of saturated fatty acids increased the yield of milk fat.

When the concentrate mixture containing 5% ‘oleic acid’ was given to the cows, the yields and percentages of the fatty acids from 4:0 to 16:0 (except 12:0) in the milk fat were decreased, but the yields and percentages of 18:0 and 18:1 were increased. Similar but more pronounced effects on the yields and percentages of the fatty acids from 4:0 to 16:0 (except 12:0) in the milk fat were observed when the cows were given the concentrate mixture containing 10% ‘oleic acid’, but under these dietary conditions the yield and percentage of only 18:1 in the milk fat were increased. The addition of the mixture of saturated fatty acids to the concentrate mixture decreased the percentages of the fatty acids from 4:0 to 14:0 (except 12:0) in the milk fat but decreased the yields of only 10:0 and 14:0; the yields and percentages of 16:0 and 18:1 were increased.

When the cows were given the concentrate mixture containing 5% ‘oleic acid’ there was a small but significant decrease in the acetic acid:propionic acid ratio in the rumen liquor. A similar but more pronounced change in the acetic acid:propionic acid ratio in the rumen liquor was observed when the cows were given the concentrate mixture containing 10% ‘oleic acid’, but in this instance there was a significant reduction in the concentration of total volatile fatty acids in the rumen liquor. Apart from a small increase in the relative proportion of propionic acid, the addition of the mixture of saturated fatty acids to the concentrate mixture had no effect on the concentrations of volatile fatty acids in the rumen liquor.

Kefir is a refreshing fermented milk with a slightly acidic taste obtained by incubating milk with kefir grains (Saloff-Coste, 1996). Kefir grains are a complex mixture of lactic acid bacteria and yeasts in a strong and specific association. They are characterized by an irregular form, a folded and uneven surface and a white or slightly yellow colour. They are tough and resilient and have a characteristic acid taste (Bottazzi et al. 1994). The basic microflora contains lactococci, homofermentative and heterofermentative lactobacilli, yeasts and acetic acid bacteria (Bottazzi et al. 1994; Rea et al. 1996). Among the yeasts isolated from grains and identified are Candida kefir, Saccharomyces cerevisiae, Sac. delbrueckii, Cand. holmii, Sac. unisporus and Sac. lipolytica (Angulo et al. 1993; Marshall, 1993; Garrote et al. 1997). Lactobacillus brevis, Lb. viridescens, Lb. casei, Lb. kefir, Lb. kefiranofaciens, Lb. kefirgranum, Lb. parakefir, Leuconostoc spp. and Lactococcus lactis are among the lactic acid bacteria present in the grains (Marshall et al. 1984; Toba et al. 1991; Takizawa et al. 1994; Garrote et al. 1997). The mixed microflora of yeasts and bacteria is held together by a matrix containing (g/kg dry weight) protein 340, polysaccharide 470 (Ottogalli et al. 1973).

The study of kefir grains in milk has been centred on the characteristics of the polysaccharide produced by lactobacilli within the grain (Yokoi et al. 1991). This polysaccharide, named kefiran, is composed of glucose and galactose (Yokoi et al. 1991). It has been suggested that proteins are incorporated from the growth media (Bassette & Acosta 1988), but no details about structure and composition are available.

Soyabeans are an important component of the diet in many countries and have been used to obtain fermented products such as sogurt (Mann, 1991). Special attention has been given to the growth of, and sugar utilization by, Bifidobacterium spp., Lb. delbrueckii subsp. bulgaricus and Streptococcus thermophilus in soya milk (Buono et al. 1990; Murti et al. 1993; Ankenman Granata & Morr, 1996). To our knowledge, there have been no attempts to ferment soya milk with kefir grains.

The aim of this study was to investigate the growth of kefir grains in soya milk and the composition of these grains, focusing on the matrix proteins.

1. Commercial samples of milk of Swiss origin, sterilized by rapid heating to high temperatures, developed a positive phosphatase reaction on storage.

2. The optimum temperatures of storage for the development of this positive phosphatase reaction was 30° C.

3. These commercial samples were sterile when received and remained sterile during storage.

4. The developed phosphatase is apparently identical with the normal alkaline phosphatase of raw milk as judged by (a) heat stability, (b) pH optimum and rate of hydrolysis at different pHs, (c) comparison of results by Kay-Graham and Aschaffenburg & Mullen tests.

Two trials were conducted to investigate the effect of pre-milking teat dipping (PMTD) on mastitis caused by environmentally associated pathogens. The first trial showed considerable variation in effect between herds, so a second, larger trial was conducted. In this second trial a comparison of the rate of clinical mastitis was made between nine matched pairs of dairy herds over 24 weeks of the winter housed period. All herds were near the national average incidence of mastitis before the trial. One member of each pair used their normal method of udder preparation throughout the trial and disinfected all teats after milking with an iodophor disinfectant. In the other nine herds the preparation of all teats, at all milkings, included dipping in a 0·25% available iodine disinfectant, which was left on the teat for 30 s. Every teat was then wiped with a paper towel before cluster attachment. There was no difference in the overall rate of mastitis or the incidence of mastitis caused by any particular type or group of pathogens between the trial groups of herds. Both groups showed a reduction in mastitis compared with the previous winter. Although there were apparent benefits in some pairs of herds there was no overall benefit. In comparison with the previous winter the control herds reported a greater reduction in mastitis than the PMTD herds. The effect of trial supervision on normal practice gave a benefit which overwhelmed any effect of PMTD. There appeared to be no effect of PMTD on the total bacterial count, cell count or iodine content of bulk tank milk. There appears to be no justification for wholesale use of PMTD although most farms and risk groups could benefit from better attention to conventional mastitis control.

The effect of homogenization on the heat stability characteristics of milk was examined. The heat stability of homogenized milk, as determined by the time taken for protein clots to form when heated at 140 °C, was reduced with increasing pressure in the range 3·5–34·5 MPa. The heat stability of homogenized milks was greater for samples obtained in the summer months than for those obtained in the winter. The general destabilizing effect of homogenization could be partly offset by 2-stage homogenization (20·7 MPa followed by 3·5 MPa), addition of phosphate stabilizers (0·08% w/v) or homogenization at a high temperature (65 °C). Whilst homogenized and unhomogenized milks reacted similarly to the addition of Ca, phosphate stabilizers, sulphydryl-blocking and oxidizing agents, the effects of season, addition of urea or formaldehyde were different for homogenized milk.

Whole cells of Lactobacillus delbrueckii subsp. bulgaricus CNRZ 397 (Lb. bulgaricus CNRZ 397) are able to hydrolyse α- and β-caseins. We have isolated a mutant of Lb. bulgaricus altered for growth in milk and unable to hydrolyse α- or β-casein. Normal growth was restored by adding amino acids or tryptone to milk. No significant difference between the peptidase activities of parent and mutant strains was observed. The cell surface caseinolytic activities of three lactobacilli species and Lactococcus lactis subsp. lactis (Lc. lactis) were compared. As expected, the characteristics of the cell surface proteinase activity of Lb. casei were similar to those of Lc. lactis. We showed that the cleavage specificities of the cell surface proteinase activities from lactobacilli were species-dependent and at least three types of activity were distinguished. The regulation of the biosynthesis of cell surface proteinase activities was medium-dependent and different within the Lactobacillus genus and even within the Lb. delbrueckii species. In contrast to Lb. bulgaricus, the cell surface proteinase activity of Lb. lactis was totally inhibited in a medium rich in peptides or amino acids. In contrast, the cell surface of Lb. helveticus probably displayed two proteinases with different cleavage specificities and with a biosynthesis regulation sensitive to different medium components.

Some media available for the isolation and enumeration of starter cultures employed for the manufacture of cheese, yogurt and bio-yogurt were examined. Reddy's medium or a modification of Elliker's medium was found to be most satisfactory for Lactococcus spp., while trypticase phytone yeast (TPY) agar with a mixture of antibiotics proved suitable for the discrete enumeration of Bifidobacterium spp. The inclusion of Prussian blue (PB) in reinforced clostridial medium or tryptone proteose peptone yeast extract (TPPY) agar gave excellent differential counts for the starter bacteria in yogurt even when the culture was imbalanced, while TPPY (PB) agar allowed the visible separation of all four of the organisms that might be found in a typical bio-yogurt, namely Lactobacillus delbrueckii subsp. bulgaricus, Streptococcus thermophilus, a, Bifidobacterium sp. and Lb. acidophilus. It was noted that variation among different strains of any given species could change the expected reactions, so for quality control purposes the suggested media may need to be modified to cope with the specific cultures in use.

Gelation is a significant operation in dairy processing. Protein gelation can be affected by several factors such as temperature, pH, or enzyme addition. Recently, the use of ultrasonication has been shown to have a significant impact on the formation of whey protein gels. In this work, the effect of ultrasonication on the gelation of casein systems was investigated. Gels were formed by the addition of 7·6 mm Tetra Sodium Pyro Phosphate (TSPP) to 5 wt% micellar casein (MC) solutions. Sonication at 20 KHz and 31 W for up to 30 min changed the surface hydrophobicity of the proteins, whereas surface charge was unaltered. Sonication before the addition of TSPP formed a firm gel with a fine protein network and low syneresis. Conversely, sonication after TSPP addition led to an inconsistent weak-gel-like structure with high syneresis. Gel strength in both cases increased significantly after short sonication times, while the viscoelastic properties were less affected. Overall, the results showed that ultrasonication can have a significant effect on the final gel properties of casein systems.

1. The detailed udder health records of 530 lactations have been analysed on a monthly and lactation basis, so that separate studies of the first infection rate, re-infection rate, total new infection rate and total infection and mastitis incidence for both cows and quarters could be made. These data have been used to study the relationship of stage of lactation, age and season of the year with udder infection and mastitis.

2. With advancing lactation there was a decline in the rate of first infection, reinfection, total new infection and in mastitis in infected cows and quarters.

3. In early lactation there was a marked tendency for infected cows and quarters to develop clinical symptoms.

4. During the last 4 months of lactation there was no significant rise either in infection or in mastitis.

5. There was an increase in infection and mastitis with advancing age, but infected older cows were not more liable to develop clinical symptoms than younger cows.

6. There was an indication that the longer a quarter was free from infection the greater were its chances of remaining so.

7. No major seasonal trends were found in the incidence of udder infection and mastitis, although the incidence was slightly higher in the summer months.

The phenomenon of rennet hysteresis in heated milk is essentially due to reversible heat-induced changes of calcium phosphate equilibrium which affect the second or calcium ion stage of the rennet coagulation. The phenomenon is shown not only by heated milk but also by all heated caseinate systems provided they contain sufficient calcium to permit of coagulation with rennet and enough phosphate to ensure some degree of colloidal phosphate precipitation during the heating process; its occurrence does not require the presence of micellar casein or of β-lactoglobulin, or the initial presence of colloidal phosphate. Nevertheless, rennet hysteresis is greatly increased in these heated systems if β-lactoglobulin is present owing to the formation of a calcium caseinate/β-lactoglobulin complex which in its renneted condition is much less sensitive to calcium ions than is calcium para-caseinate. The resulting relative prolongation of the second stage of the rennet coagulation renders this phenomenon more apparent by increasing the proportion of the total time occupied by the hysteresis effect.

The material surrounding the fat globules in commercial pasteurized homogenized milk was isolated by centrifugation of the freeze – thaw extract of the fat globules through a 52·5% (w/v) sucrose solution in simulated milk ultrafiltrate. The purified membrane material contained higher neutral lipid levels than fresh raw milk fat globule membrane (MFGM) material. Caseins and whey proteins, mainly β-lactoglobulin (β-lg) were found to be the major protein components of homogenized milk membrane material. Native MFGM polypeptides comprised only a small proportion of the total protein in these membranes. The total amount of membrane material isolated from homogenized milk was substantially higher than that from fresh raw milk. Analysis of homogenized milk membrane material by linear sucrose density gradient centrifugation showed a different pattern to that found with other milks, indicating the presence of new lipoprotein complexes. Commercial ultra heat treated (UHT) milks were also examined, but it was difficult to obtain isolated MFGM material free from core fat. However, fat globule fractions were isolated from these products by high speed centrifugation and these were analysed intact. Membrane material in these milks contained caseins and whey proteins (mainly β-1g). Natural MFGM polypeptides were present at extremely low levels. Phospholipid levels in UHT milk membranes were greatly reduced compared with membrane material isolated from other milks.

1. Four test organisms were used for the microbiological assay of vitamin B6. The test organisms and the forms of vitamin B6 active for them were: Saccharomyces carlsbergensis 4228 (pyridoxine, pyridoxamine and pyridoxal), Streptococcus faecalis R ATCC8043 and Str. faecium Ø51 (pyridoxamine and pyridoxal), and Lactobacillus casei ATCC7469 (pyridoxal).

2. By simultaneous assay of the test material with the four organisms the amounts of pyridoxine, pyridoxamine and pyridoxal present were determined. The differential assay technique has been improved by the use of Str. faecium, which is more specific for measuring total pyridoxamine plus pyridoxal, instead of Str. faecalis.

3. The optimum conditions for measuring vitamin B6 in milk were studied and the differential assay technique was applied in an investigation of the effect of heat on the vitamin B6 activity of milk.

4. It was found that pyridoxal accounted for about 80% of the vitamin B6 activity of raw milk, the other 20% being due to pyridoxamine.

5. In the manufacture of evaporated milk there was a marked fall in the pyridoxal and a slight increase in the pyridoxamine content. The overall loss was some 60%.

6. On storage of evaporated and of sterilized liquid milk at room temperature there was a further loss of vitamin B6 activity. Most of the residual activity in stored evaporated milk appeared to be due to a substance other than pyridoxal or pyridoxamine, possibly pyridoxine.

The present study aimed to assess the effect of information about organic production on Pecorino cheese liking and consumer willingness to pay. Mean scores of perceived liking were similar for organic cheese (OC) and conventional cheese (CC). Expected liking scores were higher for OC than for CC (P<0·001). For OC the expected liking was significantly higher (P<0·001) than the perceived liking expressed in blind conditions (negative disconfirmation), whereas for CC the expected liking was significantly lower (P<0·001) than the perceived liking expressed in blind conditions (positive disconfirmation). Consumers assimilated their liking for OC in the direction of expectations, as the difference actual vs. perceived liking was significant (P<0·001). However the assimilation was not complete, as also the difference actual liking vs. expected liking was significant (P<0·001). Consumers showed a willingness to pay OC (mean±se=4·20±0·13 €/100 g) higher than the local retail price for conventional (1·90 €/100 g) and even organic cheese (3·00 €/100 g). We conclude that the information about organic farming can be a major determinant of cheese liking and consumer willingness to pay, thus providing a potential tool for product differentiation, particularly for small scale and traditional farms.

The host–phage reactions of 20 strains of lactic streptococci currently used in cheese manufacture, and the phages active on them, were studied under a variety of conditions. The phages of the lactic streptococci conformed in their behaviour with the general behaviour of phages for other bacterial species. The burst size of phages which attack one strain of starter culture varied widely and also varied when one phage attacked different host strains. The burst size of a phage was also influenced by the host on which it was previously propagated. An increase of temperature from 30 to 37 °C the latent period, but it increased, decreased, or had no effect on the burst size. This increase in temperature also usually decreased the percentage adsorption of phage. Rennet at a concentration of 0·02 % significantly reduced the percentage adsorption of phage in sterile reconstituted milk and also in tryptone yeast-extract broth.

The overall objective of this study was to evaluate agreement between rectal (RT) and vaginal temperature (VT) measured with the same temperature loggers in dairy cows. Three experiments were conducted. The study began with a validation in vitro of 24 temperature loggers comparing them to a calibrated liquid-in-glass thermometer as a reference method. The association and agreement between the 24 temperature loggers with the reference method was r=0·996 (P<0·001) with a negligible coefficient of variance (0·005) between the loggers. In-vivo temperature loggers were tested in 11 healthy post-partum cows (Experiment 2) and 12 early post-partum cows with greater body temperature (Experiment 3). Temperature loggers were set to record VT and RT at 1-min intervals. To prevent rectal and vaginal straining and potential expulsion of temperature logger an epidural injection of 2·5 ml of 2% Procain was administered. Association between RT and VT was r=0·92 (P<0·001; Experiment 2) and r=0·94 (P<0·001; Experiment 3) with a negligible difference of −0·1 and 0·01 °C. Bland-Altman plots demonstrated agreement between RT and VT for healthy and early post-partum cows with greater body temperature in Experiments 2 and 3, respectively. Furthermore the intra-class correlation coefficient between RT and VT measured with identical loggers within cows of Experiments 2 and 3 also demonstrated greater agreements (P<0·001). Therefore, continuous VT monitoring with temperature loggers can be used as a measure of body temperature in dairy cows.