Kefir is a traditional fermented milk originating many centuries ago in the Caucasian mountains. It is produced by fermentative activity of ‘kefir grains’ consisting mainly of lactococci, lactobacilli and yeasts in a protein–polysaccharide matrix. The grains contain a relatively stable and specific balance of microorganisms which exist in a complex symbiotic relationship. The grains grow in the process of kefir making only from pre-existing grains (Saloff-Coste, 1996). When kefir grains are allowed to grow in milk, microorganisms are shed from the grains into milk where they continue to multiply with the production of acid, flavour and physicochemical changes.

The traditional method of kefir making is currently by adding kefir grains directly as starter to milk that has been pasteurized and cooled to 20–25°C. After a period of fermentation lasting ∼24 h, the grains are removed by filtration and the beverage is ready for consumption (Saloff-Coste, 1996). Kefir from which the grains have been removed may be used as starter. However, this fermented milk cannot be used for subsequent inoculations to make an acceptable product, because the original balance of microorganisms has been disrupted (Kroger, 1993).

The complex microbiological composition of kefir grains explains why it is difficult to obtain starter with the optimal and constant composition necessary for a regular production of kefir of standard quality (Koroleva, 1988a). Studies have been undertaken to establish cultivation conditions[ratio ]grain[ratio ]milk ratio, cultivation temperature, period of time and conditions prior to separation of grains from the fermented milk, shaking conditions for agitation of milk with the grains in the course of fermentation, washing of kefir grains and so on. All these factors influence the microflora of the kefir starter and fermented milk. There are no rules about household manufacture of kefir. Different reports indicate a wide range of grain[ratio ]milk ratios for kefir making. Bottazzi & Bianchi (1980), Marshall & Cole (1985), Merin & Rosenthal (1986), Mann (1989), Hosono et al. (1990) and Kroger (1993) employed 20–50 g/l while Koroleva (1988a) employed 20–100 g kefir grain/l and Marshall et al. (1984) and Neve (1992) 50–100 g/l. Rea et al. (1996) used 1 g kefir grain/l as starter and 200 g starter in the form of kefir grains is recommended by Hansen for the fermentation of 1 l milk (Marshall & Cole, 1985). A critical control point in kefir manufacture to obtain a product with constant quality is the standardization of the kefir grain[ratio ]milk ratio. Koroleva (1988b) claimed that it is better to use kefir grains as starter for kefir production and, at the same time, to decrease the amount of inoculum.

The purpose of this study was to evaluate the effects of changes in the kefir grain[ratio ]milk ratio (quantity of kefir grains inoculated into the milk) on microflora composition, acidity, apparent viscosity and carbon dioxide content of fermented milk.

Accurately assessing the economic impacts of diseases and other factors that affect milk production requires that the demand for milk be taken into account. Because demand for milk in the USA is relatively inelastic (i.e., consumers generally purchase a somewhat fixed amount over a given time frame, regardless of fluctuations in price), consumers tend to reap much of the benefit of enhanced production. An examination of the economic impacts of Johne's disease indicated that reduced milk production, associated with the determination of dairy operations as Johne's-positive, reduced consumer surplus by $770 million ± $690 million, and resulted in a total loss of $200 million ± $160 million to the US economy in 1996. Most of the economic surplus lost by consumers was transferred to producers, whose economic surplus increased by $570 million ± $550 million as a result of the reduced milk production associated with Johne's disease. Uncertainty analysis showed that the estimated reduction in milk production on Johne's-positive dairy operations accounted for most of the uncertainty in the economic-impact estimates. If Johne's disease had not been present on US dairy operations, then an additional 580 million ±460 million kg of milk would have been produced, but the price would have fallen by 1·1±1·0 cents/kg, and the total value of the milk would have decreased by $580 million ± $560 million.

The contamination of pasteurized milk by Bacillus cereus during the filling process was studied in two dairy plants. Samples of pasteurized milk were taken at four different sites along the production line. The samples were stored at 7 °C for 7 d, or at 10 °C for 5 d, before plate counting and random selection of B. cereus isolates. Isolates of B. cereus were typed by the polymerase chain reaction (PCR)-based method randomly amplified polymorphic DNA (RAPD). Samples taken at three different sites between the pasteurizer and the filling machine were all holding similar low concentrations of B. cereus, while an increase of the B. cereus count was seen in the consumer packages. More B. cereus of different RAPD types was growing in the consumer packages than in samples taken just before the filling machine. Several RAPD types found in the consumer packages were not detected in the samples taken just before the filling machine.

Additions of potassium iodate to milk at 0·05 and 0·1 mM (10 and 20 ppm) before UHT treatment markedly reduced the rate at which pressure built up during processing. This permitted the use of longer processing times before unacceptable pressures were reached in the heat exchangers. Iodate reduced the amount of protein deposited, particularly in the higher temperature sections of the plant, but had no effect on the deposition of minerals. The more compact nature of the highly mineral deposits offered less resistance to the flow path. Reduction in the amount of protein deposited is likely to be caused by increased denaturation of β-lactoglobulin and oxidation of heat activated sulphydryl groups by the iodate, thus reducing the formation of high molecular weight polymers of sulphur-containing proteins at the heated surfaces. Increasing the level of sulphydryl groups in the milk through the addition of L-cysteine-HCl caused an increase in the amount of deposit formed during UHT treatment. Whilst little detrimental effect on the quality of the milk resulted from additions of iodate at 0·05 mM, milks with 01 mM-iodate became bitter during subsequent aseptic storage. Bitterness was a result of iodate-induced proteolysis of casein.

The influence of diet quality and stage of lactation on Cheddar cheese moisture and yield were segregated and the effects of other potential variables (cow breed, milk protein genotype, age and level of mastitis) were minimized. An experiment was conducted using milk of cows in mid lactation or late lactation fed on high or low quality diets. Increased moisture in cheese was largely due to the influence of cow diet. Milk from cows given high quality diets produced lower moisture cheese. Cheese yield was influenced by diet and stage of lactation. Cows in late lactation fed on high quality diets always gave milks yielding the most cheese. Fat and protein recovery in cheese was not influenced by diet or stage of lactation. The results suggest that low quality diets may induce changes in the complex interactions of milk proteins and other components that affect cheesemaking.

The effects of the isocaloric replacement of part of the dietary concentrate mixture by 5% lauric acid (99% pure) or by 10% of myristic (95% pure), palmitic (96% pure) or stearic (94% pure) on the yield and composition of milk fat was investigated in 2 feeding experiments with a total of 10 cows in mid-lactation. The concentrate mixtures were given with a high-roughage diet that supplied 9·1 or 7·7 kg hay/day in expts 1 and 2, respectively.

In expt 1 the inclusion of myristic acid in the diet decreased the yields of milk and solids-not-fat (SNF), but increased the percentage of fat in the milk without altering the fat yield. When stearic or palmitic acid was included in the diet there was an increase in milk fat yield; palmitic acid caused the greater increase. In expt 2 the inclusion of lauric acid in the diet did not appear to affect the yields of milk or SNF but it caused large reductions in the percentage of fat in the milk and in the yield of fat.

In expt 1 the inclusion of myristic acid increased the yields and percentages of 14:0, 14:1 and 16:1 in the milk fat and decreased the yields and percentages of the short-chain fatty acids (4:0–8:0), 16:0, 18:0 and 18:1. When palmitic acid was included in the diet there were increases in the yields and percentages of 16:0 and 16:1 in the milk fat and decreases in the yields and percentages of 10:0, 12:0, 14:0, 18:0 and 18:1. The inclusion of stearic acid in the diet increased the yields and percentages of 18:0 and 18:1 in the milk fat and decreased the yields and percentages of 12:0 and 16:0. In expt 2 the inclusion of lauric acid in the diet increased the yield and percentage of 12:0, and in 1 cow the content of 14:0 in the milk fat; there were reductions in the yields and percentages of all the other fatty acids in the milk fat. There was no evidence of any marked elongation of the carbon chains of 12:0 and 14:0 in the mammary gland to form 16:0 or 18:0.

In expt 1 the incorporation of myristic acid in the diet decreased the concentration of total steam-volatile fatty acids in rumen liquor. The inclusion of either myristic, palmitic or stearic acid in the diet had little effect on the relative proportions of the individual volatile acids in the rumen liquor. In expt 2 the addition of lauric acid to the diet reduced the acetic acid:propionic acid ratio in the rumen liquor.

After extended tryptic hydrolysis of large bovine casein micelles, a mineral-rich peptide fraction was recovered by ultracentrifugation. Its mineral part contained 72% of the colloidal Ca and 49% of the colloidal Pi originally present in the native micelle. Colloidal nitrogenous components were also present, amounting to 27% of the original N content. They contained most of the phosphopeptides and 82% of the micellar phosphoseryl residues. These tryptic peptides were characterized by reversed-phase HPLC on-line electrospray ion source–mass spectrometry analysis. Among the peptides produced 14 phosphopeptides were identified: αs2-CN(l–24), αs2-CN(1–21), αs1-CN(43–79), αs1-CN(35–79)7P, αs1-CN(35–79)8P, αs1-CN(37–79), αs1-CN(104–119), αs1-CN(104–124), β-CN(1–25), β-CN(1–28), β-CN(1–29), β-CN(30–97), β-CN(33–97) and β-CN(29–97). The proportion of the phosphopeptides interacting with colloidal calcium phosphate was correlated with their relative content of phosphoserine residues, since phosphopeptides containing more than four phos-phoserine residues were consistently present within this fraction. It also appeared that other types of peptides, some of them hydrophobic in nature, were also partly or completely present within the colloidal fraction, including αs1-CN(91–100), αs1-CN(152–193), αs1-CN(23–34), αs1-CN(125–193), αs1-CN(125–199), β-CN(177–209), β-CN( 184–209), β-CN(114–169) and β-CN(108–169). Their possible involvement in the micellar backbone is discussed.

Three groups of 12 lactating Comisana ewes were housed in separate rooms of the same building that contained straw-bedded pens with total areas of 12, 18 and 24 m2. The ewes were assigned to groups with different stocking densities: high (HSD, 1 m2/animal), medium (MSD, 1.5 m2/animal) or low (LSD, 2 m2/animal). The LSD treatment resulted in lower air concentrations of total microorganisms and coliform bacteria than the other two. Ewes in the LSD group gave greater yields of milk, total protein and fat than those in the other two groups. LSD treatment increased milk casein content and improved clotting time and clot firmness. LSD also resulted in ewes giving milk with lower somatic cell counts and smaller concentrations of mesophiles, psychrotrophs and faecal coliforms than MSD and HSD. Subclinical mastitis occurred in three ewes of the MSD group and four ewes of the HSD group, while no cases were recorded in the LSD group. These results indicate that stocking density is a critical factor in dairy sheep housing and suggest that a space allocation <2 m2/animal may adversely affect the performance and health of the lactating ewe.

In the later stages of the reaction between rennin and casein drastic viscometric methods are undesirable, but in the first stages there is a fall in viscosity which may be satisfactorily measured in an Ostwald viscometer. Using fat-free milk, the viscosity at first falls linearly with time. At low rennet concentrations (Ce) this may be said to constitute a zero-order reaction (constant k0). At higher rennet concentrations and after longer times, the reaction passes to first order (constant k1). After very long times it doubtless becomes more complex.

The values of k0 are proportional, over a considerable range, to the milk concentration (Cm), those of k1 being independent of Cm.

For pure rennin k0 and k1 are proportional to Ce, but for commercial rennets they vary as a power (N) of Ce and the value of N appears to measure the rennin purity. The potentialities of the method for assessing rennet activities are also discussed.

If the reduced viscosity (specific viscosity÷Cm) of fat-free milks is plotted against Cm, good straight lines are obtained which may be extrapolated to zero concentration to give a reliable value of intrinsic viscosity. The intrinsic viscosity falls progressively during the protein breakdown process but the slope of the curves (‘second order term’) remains unchanged.

Several media previously recommended for lactobacilli by other workers have been examined, but none was found to support good growth of all species. Experiments are described in which the optimum concentrations and combinations of various ingredients, particularly Tween 80, were determined. These resulted in the development of a practical medium which has proved satisfactory for the growth of all varieties of lactobacilli.

For its characteristics, donkey milk has been proposed as an alternative to goat or artificial milk to feed allergic infants. Therefore, it is important to increase our knowledge on health and immunological characteristics of donkey milk. Ten donkeys, bred as companion animals, were enrolled in this study and sampled once a month, for eight months. Milk (10 ml) was collected from each half udder for somatic cell count (SCC), bacteriological analysis and total bacteria count (TBC). The major pathogens were tested for antimicrobial susceptibility, and Staphylococcus aureus isolates were further genotyped by nanoarray analysis. Whey lysozyme and NAGase (NAG) activities were also assessed. Overall, 101 half-udder milk samples were taken. They showed very low values of TBC (<250 cfu/ml) and SCC (<50 000 cells/ml) and a minor prevalence of pathogens: Staph. aureus was isolated only from 5 milk samples (3 animals), Streptococcus equi from 2 samples and Str. equisimilis from a single sample. All the isolates were sensitive to all antibiotic classes used in veterinary medicine. None of the Staph. aureus isolates were shown to harbour genes coding for any enterotoxin, toxic-shock syndrome toxin or antibiotic resistance. Lysozyme levels were always very high (4000–5000 U/ml), while NAG values were mostly low (<50 U/ml), out of the last part of lactation. The results of this study confirmed the low prevalence of intramammary infections in donkey and the absence of food-borne pathogens, suggesting that donkey milk could be a safe food, if the mammary gland is healthy and the animals are milked in proper hygienic conditions.

Mixed cultures of different EPS-producing Streptococcus thermophilus strains in combination with a Lactobacillus delbrueckii subsp. bulgaricus strain with negligible EPS-production were used for yoghurt production. The yoghurt texture was characterised with respect to sensory, rheological and microstructural properties and the EPS-concentrations were determined. The cultures resulted in yoghurts with highly different texture properties, and positive interactions between certain Streptococcus thermophilus strains were observed. The underlying properties of yoghurt texture are multidimensional, but a number of microstructural characteristics were apparent in the yoghurts with the highest mouth thickness, creaminess and viscosity. A strong protein network, not too dense and with medium size pores containing EPS, seems associated with these properties. The presence of capsular polysaccharides (CPS) also appeared to be beneficial as did a combination of EPS types, which were distributed differently in the protein network (in serum pores, respectively in association with protein). Obviously, a certain concentration of EPS must be present to provide for these effects on yoghurt texture, but other factors than concentration per se seem more important.

Fouling from milk fluids is a severe industrial problem which reduces the efficiency of process plant. The chemistry of fouling has been thoroughly investigated but the sequence of events that occur is not yet clear. Deposit contains both protein and minerals. Experiments have been carried out to determine the sequence of events in the fouling of stainless steel surfaces at 96 °C from turbulent flows of whey. Contact times between 4 and 210 s have been studied, and surface analysis techniques used to detect the distribution of elements. The first layer of deposit, formed after 4 s of contact between the fluid and the surface (fluid temperature 68 and 73 °C), consisted mainly of protein and was identified by X-ray photoelectron spectroscopy analysis. There was a lag phase of up to 150 s for a fluid temperature of 73 °C before deposit aggregates were observed to adsorb on to the surface. These aggregates were identified as protein and Ca by X-ray elemental mapping. No P was found in any experiments for this exposure. After 60 min contact time, however, both Ca and P were found at the interface between deposit and the stainless steel surface, irrespective of the Ca and P content of the test fluid.

Parmigiano Reggiano is a hard, cooked cheese produced in specific areas of Northern Italy. The raw material is obtained by mixing the partly skimmed evening milk and whole morning milk. The mixture is then heated to 22°C, and natural whey starter is added at 28–30 g/l after 1–2 min, bringing the pH of the mixture to 6·2–6·3. After coagulation, which takes ∼15 min and occurs at 32–33°C owing to the addition of calf rennet powder, the curd is broken up for 2–4 min, cut into fragments and cooked at a temperature raised gradually to 42–44°C and then more quickly to 55–56°C over 10–15 min. The curd is left undisturbed, covered by the whey, for 40–60 min, then removed and placed inside a circular wooden mould. The cheese is held at ∼20°C for 3 d during which it is turned at frequent intervals to facilitate complete whey drainage. The cheese, which now has its typical shape and size, is then salted by immersion in brine (260–280 g NaCl/l at 16–17°C) for 20–24 d. During this period the cheese absorbs 15–18 g NaCl/kg and its weight decreases by 4%. During the subsequent period of ripening (12–24 months) in store rooms at 16–18°C and 85% moisture, the cheese is frequently turned. At the end of ripening the cheese is cylindrical in shape, with a slightly convex side, 0·22–0·24 m high, 0·40–0·45 m diam. weighs 35–36 kg, has 320–330 g fat/kg dry matter and a minutely granulated internal structure with small holes formed by the activity of some heterofermentative lactic acid bacteria.

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.

The aim was to determine whether administration of melatonin would alter the yield and composition of milk from grazing dairy cows in summer. Twelve sets of spring-calving identical twin Friesian cows were used in the experiment. In late-November (late spring), one twin from each set was given slow-release melatonin implants behind the ears (108 mg melatonin/cow). Two further implantations occurred at 4-weekly intervals to maintain increased circulating concentrations of melatonin for 12 weeks. The other twin served as a control. Milk yield and composition were measured twice prior to treatment and then four times over the following 12 weeks. Concentrations of melatonin, prolactin and insulin-like growth factor 1 (IGF-1) were measured in blood plasma twice before treatment and then either seven (melatonin and prolactin) or three (IGF-1) further times during the experiment. Management procedures for all cows were similar and cows grazed a daily pasture allowance of approximately 30 kg DM/cow as their sole feed source. In melatonin-treated cows there was a decrease in mean concentrations of prolactin in plasma, but concentrations of IGF-1 did not change. Melatonin reduced milk yield by 6 weeks after treatment and by the end of the 12-week experimental period milk yield in melatonin-treated cows had fallen by 23%. Melatonin also reduced concentrations of lactose in milk, but increased concentrations of fat, protein and casein, changes that were broadly similar to those that occur in late lactation in seasonally calving dairy cows. Thus, the results suggest that some of the variation in the volume and quality of milk throughout the season in New Zealand dairy systems may be due to changes in photoperiod mediated by increased concentrations of plasma melatonin in association with decreased concentrations of plasma prolactin.

The trypsin-inhibitor capacity of bovine milk was seen to increase in mastitits. This capacity showed good correlation with the California Mastitis Test score, somatic cell count (Coulter Counter method) and bovine serum albumin (BSA) content (radial immunodiffusion). The elevated antitrypsin level proved to be a safer indicator of mastitis than BSA alone. Using gel-filtration chromatography, the major trypsin-inhibitor activity of mastitic milk and plasma was eluted with BSA, indicating a similar mol. wt (70000). This fraction showed electrophoretic polymorphism. A large molecular weight fraction cross-reacted immunologically with human α2-macroglobulin. The antitrypsin activity in mastitic milk was clearly different from the principal activity in colostrum, which had a mol. wt of about 13000.

Numerous methods based on DNA analysis have been employed in the food industry to monitor adulterations of food products of animal origin. Among them the most frequently used are: polymerase chain reaction (PCR) amplification of a marker gene fragment(s) with universal primers, or amplification of DNA with species-specific primers. PCR-products of different origin can be discriminated by size, restriction fragment length polymorphism (RFLP) or single stranded conformational polymorphism (SSCP) analysis. These methods have been used for identification, and differentiation between, the animal origins of raw or heat-treated meat and meat products (Chikuni et al. 1994; Meyer et al. 1994, 1995; Zehner et al. 1998; Behrens et al. 1999; Guoli et al. 1999; Hopwood et al. 1999; Matsunaga et al. 1999; Wolf et al. 1999). These approaches are also applicable to the analysis of dairy products. However, adulterations of goats' milk and its products are traditionally tested by immunological and/or electrophoretic methods (Amigo et al. 1992; Levieux & Venien, 1994; Mimmo & Pagani, 1998). So far, only a few DNA-based techniques designed to detect the presence of bovine DNA in goats' milk have been described (Plath et al. 1997; Branciari et al. 2000). This paper presents a one-step PCR procedure for detection of adulteration of goats' milk with cows' milk. The method, employing bovine-specific primers for amplification of a 274 bp fragment of cytochrome b DNA, seems to be simple, fast, specific and sensitive.

Thirty-nine multiparous Holstein cows were used to measure the effect of propylene glycol treatment around parturition on milk yield, reproductive efficiency and some hormone and metabolite concentrations. Cows were assigned randomly to control (n = 19) or propylene glycol treated (n = 20) groups. Propylene glycol (300g) was administered directly mixed with the diet from day 10 prior to the expected calving date until parturition (day 0) and orally after dilution in 1 l water on days 3, 6, 9 and 12. Blood samples were collected on days −20, −5, 0, 3, 10, 25 and 50 while milk samples were taken weekly until 13 weeks post partum. Body condition scores, recorded on days −20, 15 and 50, were not affected by propylene glycol administration. Propylene glycol did not significantly affect milk yield or composition but linear somatic cell score measured from the first 13 weeks post partum was reduced by propylene glycol administration (P < 0·01). Moreover, propylene glycol reduced milk urea (−25 mg/l, P < 0·05), especially during the first 9 weeks post partum. Plasma insulin concentrations were similar in both groups during the experiment while insulin-like growth factor I (P < 0·05) and insulin-like growth factor-binding protein 3 (P < 0·001) levels were higher on days 10, 25 and 50 post partum in the propylene glycol group. Propylene glycol administration decreased plasma non-esterified fatty acid concentrations (P < 0·05 to P < 0·01) but increased total cholesterol levels (P < 0·01) after parturition while 3-hydroxy-butyrate levels were unaffected by the treatment. Changes in the hormone and metabolic concentrations after propylene glycol administration in the last few days of gestation and the first week of lactation seem to indicate that energy balance in the treated group was probably more positive than in the control group. There was also evidence that propylene glycol administration prevented fatty liver syndrome and hastened the resumption of oestrous cycles (P < 0·001).