A major problem in camel productivity is the high mortality rate of camel calves in the first 3 months. The causes for mortality are mainly poor management practice and infectious diseases. The purpose of this research, carried out on a ranch in Kenya, was to determine the immunoglobulin G (IgG) concentration in camel colostrum as well as the extent of the calves' passive immunization by maternal antibodies. IgG concentration in colostrum and in the serum of the calf were measured during the first 3 d of life. Evaluation was carried out by comparing the respective values with those for horses and cattle. The average IgG concentration in the camel colostrum was higher than that found in literature for horses and cattle. IgG concentration in the serum of the camel calves reached its maximum 24 h after birth. In 39% of the examined calves, this maximum concentration was below 4 g/l, which is considered to be the critical value in horses and cattle. 61% of the calves achieved an IgG concentration of over 4 g/l. Since there is no correlation between IgG level in colostrum and early mortality, the results indicate that low colostrum intake during the first 24 h of life and not low IgG concentration in colostrum is presumably one of the main causes of early calf mortality. Therefore, it was recommended that the care of the newborn calves by herdsmen should be improved.

The somatic cell count of milk is routinely determined by the fluoro-opto-electronic method and sometimes by the direct epifluorescent filter technique (DEFT). This paper investigates the potential of solid phase cytometry (SPC), a novel technique combining aspects of both the fluoro-opto-electronic method and epifluorescence microscopy for somatic cell counting. In SPC, cells are retained on a membrane filter, fluorescently labelled and automatically detected on the entire membrane filter by means of a laser scanning instrument (ChemScan). Fluorescent spots can be visually inspected by an epifluorescence microscope with a computer-driven moving stage. The performance of SPC was compared with that of the fluoro-opto-electronic method using a Fossomatic 360 instrument for 68 milk samples with varying somatic cell counts (103–106/ml). The sample throughput and repeatability of SPC were inferior to those of the Fossomatic method and statistical analysis of the method comparison data using the approach of J. M. Bland & D. G. Altman (The Lancet 1986 February 8 pp 307–310) revealed a poor comparability between the two methods. Moreover, problems of milk filterability and the interference of fluorescent particles presently hamper the routine application of SPC. Nevertheless, this method represents the first example of the application of SPC to milk.

Cows managed for extended lactations of 16 months duration were milked on a half-udder basis twice or thrice daily, commencing in lactation week 9. Mammary epithelial integrity (assessed by milk sodium[ratio ]potassium ratio) was greater in the half-udder which was milked thrice daily. This difference was evident throughout the lactation but became greater after week 41. Milk protein composition was assessed during late lactation (52±3 weeks). Casein number (casein as a proportion of total protein) was significantly higher in half-udders milked thrice daily, as were the relative amounts of α- and β-caseins, whilst those of κ- and γ-caseins were reduced. Two days of inverted milking frequency (i.e. thrice-milked udder halves now milked twice, and vice versa) only partly reversed these differences. We concluded that thrice-daily milking will help to prevent or ameliorate the usual decline in milk processing quality associated with late lactation. Part of this effect is due simply to reduced exposure to proteolytic enzymes as a result of decreased storage time in the udder, but part is due to a better maintenance of epithelial tight junction integrity as lactation advances, which restricts leakage of proteolytic enzymes from serum into milk.

To test the hypothesis that the availability of glucose or its precursors can influence the response of milk protein concentration to the intravenous infusion of amino acids, five cows were used in a 5 × 5 Latin square design with period lengths of 7 d. The five treatments were the basal diet of grass silage ad lib. plus 5 kg/d of a cereal-based supplement containing feather meal (Basal); Basal plus 4 g/d histidine, 8 g/d methionine and 26 g/d lysine (4H); Basal plus 8 g/d histidine, 8 g/d methionine and 26 g/d lysine (8H); and these two amino acid mixtures together with 600 g/d of glucose (4HG and 8HG respectively). Earlier experiments with this basal diet had shown that histidine was first-limiting for secretion of milk protein, followed by methionine and lysine. The yield of milk protein was increased progressively with the amount of histidine infused. The efficiency of transfer of histidine into milk protein was 0·42 for the 4H and 4HG and 0·35 for the 8H and 8HG treatments, and the concentration of milk protein was increased over Basal by all infusion treatments. However, milk protein concentrations were higher, and lactose concentrations in the milk were lower, in the absence of added glucose. Concentrations of insulin in blood plasma were not affected by treatment. It is concluded that, with the treatments without added glucose, a shortage of glucose prevented an increase in lactose secretion, and hence limited the increase in milk yield, leading to an increased concentration of protein in the milk.

The efficiency of reversed-phase HPLC, capillary electrophoresis (CE), PAGE and isoelectric focusing with immunoblotting in separating ovine caseins has been evaluated. The assessment was carried out by employing electrospray ionization–mass spectrometry (ESI–MS) and matrix-assisted laser desorption ionization–time of flight as reference tools for identifying protein components. Ovine casein was fractionated by HPLC into four major peaks. With ESI–MS, each peak contained components belonging to only one of the four casein families. On-line liquid chromatography–ESI–MS allowed us to determine each fraction's composition by detecting thirteen αs1-, eleven αs2-, seven β-, and three κ-casein (CN) components. The αs1-CN and αs2-CN consisted of eight and two protein chains respectively of lengths differing through the deletion of one or more peptide sequences; they were also discretely phosphorylated as κ-CN and β-CN. By CE at pH 2·5, each casein fraction was as heterogeneous as that resulting from ESI–MS for the single HPLC-derived fractions. The separation of αs1-CN and αs2-CN proved to be excellent, with the exception of a co-migration of κ0-CN with a minor αs1-CN component and of a glycosylated κ-CN form with low-phosphorylated αs1-CN and β-CN components. Dephosphorylation of whole casein was used to reduce the heterogeneity of the native fractions and by applying currently used analytical techniques it was possible to visualize the protein moiety difference along the CE profile. CE, HPLC, and immunoblotting were all equally capable of effecting an accurate separation of the four dephosphorylated casein families. The spectra obtained by ESI–MS directly on dephosphorylated whole ovine casein samples contained the signals of the four casein families and the relative αs1-CN variants, the non-allelic αs1-CN and αs2-CN forms, dimeric κ-CN and other newly formed peptides. We suggest using this procedure for rapid characterization of whole casein.

In this work the purification and the complete primary structure of κ-casein from equine milk are reported for the first time. Mares' milk casein was separated by RP-HPLC into four fractions. Complete primary sequence was obtained by sequence analysis of the protein in the fastest eluting peak isolated by chromatography. This sequence was 95% identical to that reported for the C-terminal portion of the zebras' κ-casein and showed high similarity with κ-caseins from sources other than Equidae, confirming that this protein was indeed κ-casein in equine milk. The presence of post-translational modifications in equine κ-casein was investigated by mass spectroscopy, after enzymic dephosphorylation. Two main components were found, the smaller component being more abundant. Equine κ-casein was recognized by a lectin specific for one of the glucosidic bonds in the saccharide moiety of bovine κ-casein. Sequence comparison with prevision studies showed that the distribution of charged and hydrophobic regions in equine κ-casein was similar, but not identical, to that found in the bovine protein; these regions are associated with the role of κ-casein in the formation and stabilization of the micellar structure of casein in milk.

The aim of this research was to study the effects of the CSN1AG allele on the main rennet coagulation properties of milk. The study was carried out on individual milk samples with low αs1-casein obtained from 19 Italian Brown cows heterozygous for the CSN1AG allele (seventeen CSN1A BG and two CSN1A CG) from four herds in the province of Parma (Italy). Control cows (sixteen CSN1A BB and three CSN1A BC) giving milk with normal αs1-casein levels were chosen from within the same herds in order to establish pairs of cows with identical environment and management conditions, and comparable lactation stages and numbers. Individual milk samples from single pairs of cows with somatic cell counts and lactose and chloride levels within the normal ranges were collected and analysed in parallel. Rennet coagulation properties of milk were analysed using Formagraph and Gel Tester. Milk from low αs1-casein cows was characterized by lower casein content, lower titratable acidity and a higher proportion of κ-casein in total casein. The clotting time of this milk was ∼ 23% lower than that obtained with milk from normal αs1-casein cows. Rennet curd from low αs1-casein milk was obtained more rapidly and had a higher final firmness: curd-firming time was ∼ 35% lower and curd firmness measured 30 min after rennet addition was ∼ 27 % higher compared with that for normal αs1-casein milk. In addition, curd from low αs1-casein milk had a higher resistance to compression. These results suggest that, although a role for the CSN2 locus cannot be definitely excluded, the CSN1AG allele can considerably affect the main rennet coagulation properties of milk.

Proteolysis of sodium caseinate solution (24·5 g/l) induced by heat treatment at 120 °C at different pH values was studied by measuring nitrogen content and relative fluorescence intensity in the 4% trichloroacetic acid filtrates. The low molar mass peptides corresponding to the soluble nitrogen were identified using liquid chromatography/tandem mass spectrometry. Increase in proteolysis, deduced from the increase in soluble nitrogen content, was observed with heating time (10, 20 and 30 min) and pH (6·0, 7·0, 8·0 and 9·0). The fluorescence measurements showed that the release of peptides containing tryptophan was minimal at pH ∼ 7·0. In parallel, eighteen low molar mass peptides were characterized, of which four came from κ-casein, nine from β-casein and five from αs1-casein. Peptides were preferentially released under alkaline conditions.

The effect of β-lactoglobulin and heat-induced precipitation of calcium phosphate on the pH dependence and mechanism of thermal coagulation of milk throughout the pH range 6·3–7·3 was studied using serum protein-free milk and sodium caseinate as models for micellar and non-micellar milk protein systems respectively. It appears that the specific effect of β-lactoglobulin at the pH of maximum stability may be related to its ability to chelate calcium. The effect of β-lactoglobulin at the pH of minimum stability does not appear to be directly related to heat-induced dissociation of κ-casein or micellar integrity but may be due to its ability to sensitize casein micelles to heat-induced precipitation of calcium phosphate, by increasing micellar hydrophobicity. The extent of heat-induced precipitation of calcium phosphate, as a function of pH, is an inverse reflection of the pH dependence of heat stability. Micellar integrity appears to play a critical role in the heat stability of milk but for reasons not previously appreciated.

A detailed kinetic study of alkaline phosphatase, lactoperoxidase and β-lactoglobulin was carried out in the context of identifying intrinsic time–temperature indicators for controlling the heat processing of milk. The heat inactivation or denaturation of alkaline phosphatase, lactoperoxidase and β-lactoglobulin under isothermal conditions was found to follow first order kinetics. Experimental results were analysed using both a two step linear regression and a one step non-linear regression method. Results obtained using the two statistical techniques were comparable, but the 95% confidence interval for the predicted values was smaller when the one step non-linear regression method was used, indicating its superiority for estimating kinetic parameters. Thermal inactivation of alkaline phosphatase and lactoperoxidase was characterized by z values of 5·3 deg C (D60 °C = 24·6 min) and 4·3 deg C (D71 °C = 38·6 min) respectively. For the denaturation of β-lactoglobulin we found z values of 7·9 deg C (D75 °C = 49·9 min) in the temperature range 70–80 °C and 24·2 deg C (D85 °C = 3·53 min) in the range 83-95 °C. Dref and z were evaluated under dynamic temperature conditions. To estimate the statistical accuracy of the parameters, 90% joint confidence regions were constructed.

Many psychrotrophic bacteria contaminating raw milk produce phospholipase that withstands pasteurization and UHT treatments. This enzyme acts on the milk fat globule membrane and exposes triacylglycerides to the action of lipase. Phospholipase production by various isolates of Pseudomonas was investigated. The isolates were cultured aerobically at 8 °C in nutrient broth, McKellar's minimal salts medium, Chrisope's medium, and skim milk. Each strain produced phospholipase during the 50 h incubation. Enzyme production varied significantly (P < 0·001) with strain and growth medium. Strains varied significantly (P < 0·001) in their enzyme production in each medium and during the incubation time as well. Strain, incubation time, and the growth medium significantly influenced (P < 0·001) heat stability of the enzyme activity. Pasteurization reduced the activity, but did not eliminate it in skim milk.

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.

The ability of Listeria monocytogenes to grow at low temperatures and increase to hazardous levels during storage of dairy products is of great concern to the dairy industry. List. monocytogenes was detected in 3·6% of 774 cows' milk samples from 114 farms in Central Spain (Gaya et al. 1998). Ewes' and goats' milks produced in Spain had contamination levels of 2·2 and 2·6% respectively (Rodríguez et al. 1994; Gaya et al. 1996). List. monocytogenes may survive during the manufacture and ripening of most cheese varieties, with higher risk in soft surface-ripened cheeses owing to the rise in pH during ripening (Maisnier-Patin et al. 1992; Giraffa & Carminati, 1997).

The efficacy with which actively growing bacteriocin-producing cultures inhibit List. monocytogenes in some cheese varieties has been demonstrated. Nisin-producing starters inhibited List. monocytogenes V7 in Camembert cheese (Maisnier-Patin et al. 1992) and List. innocua BL86/26 in raw ewes' milk Manchego cheese (Rodríguez et al. 1998). A lacticin 3147-producing starter culture (McAuliffe et al. 1999) reduced List. monocytogenes Scott A levels in cottage cheese. Inoculation of milk with enterocin AS-48-producing Enterococcus faecalis INIA 4 inhibited List. monocytogenes strains Ohio and Scott A during the manufacture and ripening of Manchego cheese (Nuñez et al. 1997).

Semi-hard cheese varieties from raw or pasteurized cows' milk mixed with different proportions of ewes' and/or goats' milk represent ∼ 50% of Spanish cheese production. The objective of the present work was to evaluate the antilisterial activity of three bacteriocin-producing lactic acid bacteria strains isolated from milk (Rodríguez et al. 2000) during the manufacture and ripening of a semi-hard cheese manufactured from raw milk.

Lactic acid bacteria (LAB) play an important role in food fermentation, as the products obtained with their aid are characterized by hygienic safety, storage stability and attractive sensory properties. A major aim of the research in this field is the selection of LAB strains that could be used. Hence it is very important to be able to apply a reliable method to distinguish a particular strain specifically and unambiguously, which allows studies of population dynamics of mixed cultures and monitoring starter strains during fermentation (Ramos & Harlander, 1990).

Molecular methods are a powerful alternative to the traditional differentiation of bacteria. A highly reproducible method for characterizing and distinguishing closely related strains, is represented by REA-PFGE (restriction endonuclease analysis by pulsed-field gel electrophoresis) performed by infrequently cutting endonucleases. Genetic differentiation of strains in several species of LAB has been successfully performed by this technique (Moschetti et al. 1997; Villani et al. 1997) obtaining very clear and reproducible restriction patterns (Moschetti et al. 1998).

In this study selected inoculated strains (lactococci or lactobacilli) were monitored by REA-PFGE during the whole process of water-buffalo ‘cacioricotta’ cheese-making. This product is a typical and traditional cheese in southern Italy produced from cow, goat, ewe or water-buffalo milk. The original technology of this preparation permits the recovery of whey proteins due to the high heat treatment of whole milk employed, allowing interesting yields to be achieved in terms of cheese. The use of starters is not common in traditional technology but low acid protection of the final product suggested the use of LAB as starter (Emaldi et al. 1987).

Two main genetic variants of κ-casein, A and B, are found in Holstein cows. A positive association between the κ-casein B genetic variant and milk characteristics of economic importance have been reported (reviews: Creamer & Harris, 1997; Ng-Kwai-Hang, 1998). This can be explained, at least in part, by a higher κ-casein content of the casein in milk of cows having the κ-casein B genetic variant (Donnelly et al. 1984; Law, 1993). We have recently reported the presence of a differential allele-specific expression of the κ-casein gene in Holstein cows by comparing the content of allele-A and allele-B specific mRNA in the mammocytes of lactating cows genotyped κ-casein AB (Robitaille & Petitclerc, 2000). For some cows, the A- and B-specific κ-casein gene alleles were expressed in a similar manner. These cows are named HH here to indicate that they were homozygous for κ-casein gene expression. The other group of cows, cows HL, presented a differential allele specific expression of the κ-casein gene allele B which was overexpressed compared to allele A. The genetic polymorphism governing this differential allele-specific expression of the κ-casein gene is likely to affect the physico-chemical properties of casein micelles and, hence, the technological properties of milk, as κ-casein is considered to be the stabilizing component of the milk micelles. The objective of the study was to evaluate the effect of this expression polymorphism of the κ-casein gene on milk ethanol stability.

β-Lactoglobulin (β-lg), which is found in the milk of several mammal species, is the most abundant protein in bovine whey (McKenzie, 1971). The interaction properties of β-lg with a large variety of small hydrophobic ligands have been extensively studied (Sawyer et al. 1998). β-Lg belongs to the super-family of hydrophobic molecule transporters called the lipocalins, which characteristically bind hydrophobic ligands inside a central calyx (Godovac-Zimmermann, 1988; Perez et al. 1989; Brownlow et al. 1997; Wu et al. 1997; Qin et al. 1998).

At present, whey protein concentrates containing a high percentage of β-lg are commercially available in a very large quantity, but most of the processes used in milk technology involve heat-treatments that are known to affect the initial conformational state of β-lg. Such conformational changes have consequences for both the physicochemical and functional properties in food systems, including a decrease in the availability of lysine, due to Maillard reactions (Léonil et al. 1997) and a decrease in the affinity constant for binding to retinol (Laligant et al. 1991) and to flavour compounds (O'Neil & Kinsella, 1988). In the field of protein-volatile compound interactions, we have recently reported a significant enhancement of foaming properties of β-lg solutions (50 mM-NaCl, pH 6) in the presence of aroma compounds such as isoamyl acetate (Marin & Relkin, 1999), benzaldehyde (BZA; Marin & Relkin, 2000) and vanillin (Relkin & Vermersh, 2000). The observed increase in foaming properties of β-lg was postulated to be due to formation of surface active complexes between β-lg and aroma compounds.

In the present work we have investigated the interaction between a β-lg concentrate (prepared by ultra-diafiltration on an industrial scale) and BZA; particularly, evidence was sought for the presence of covalently bound monomers, dimers and lactolated monomers.