This Research Communication aims to compare the effect of A1A2 and A2A2 cow milk diets on the biochemical and histological parameters of rats. The rats were divided into four groups and fed with a normal diet, A2 milk powder, A1A2 or A2A2 cow milk diets for 90 d. Blood glucose, kidney function, liver function and lipid profile were examined during the experimental period. The study showed an increase in the body weight of the A1A2 group whereas a slight decrease in the A2A2 group, and blood glucose levels increased from d 0 to day 90 in all experimental groups. However, none of these changes were found to be statistically insignificant (P > 0.05). Moreover, no significant changes were recorded in other parameters (serum glutamic pyruvic transferase and serum glutamic-oxaloacetic transaminase for liver function, bilirubin direct, cholesterol, triglycerides, creatinine and uric acid). The histology of the liver, kidney and pancreas also showed no changes in all groups. Overall, this study revealed no significant difference in the nutritional values of A1A2 and A2A2 milk types and hence equally beneficial for health. Although the present study showed no significant difference in the effect of both milk types in 90 d, further studies might be conducted to evaluate their longer term effects.

Despite the well-characterised mechanisms of amino acids (AA) regulation of milk protein synthesis in mammary glands (MG), the underlying specific AA regulatory machinery in bovine MG remains further elucidated. As methionine (Met) is one of the most important essential and limiting AA for dairy cows, it is crucial to expand how Met exerts its regulatory effects on dairy milk protein synthesis. Our previous work detected the potential regulatory role of seryl-tRNA synthetase (SARS) in essential AA (EAA)-stimulated bovine casein synthesis. Here, we investigated whether and how SARS participates in Met stimulation of casein production in bovine mammary epithelial cells (BMEC). With or without RNA interference against SARS, BMEC were treated with the medium in the absence (containing all other EAA and devoid of Met alone)/presence (containing 0·6 mm of Met in the medium devoid of Met alone) of Met. The protein abundance of β-casein and members of the mammalian target of rapamycin (mTOR) and general control nonderepressible 2 (GCN2) pathways was determined by immunoblot assay after 6 h treatment, the cell viability and cell cycle progression were determined by cell counting and propidium iodide-staining assay after 24 h treatment, and protein turnover was determined by l-[ring-3H5]phenylalanine isotope tracing assay after 48 h treatment. In the absence of Met, there was a general reduction in cell viability, total protein synthesis and β-casein production; in contrast, total protein degradation was enhanced. SARS knockdown strengthened these changes. Finally, SARS may work to promote Met-stimulated β-casein synthesis via affecting mTOR and GCN2 routes in BMEC.

The study reported in this Regional Research Communication aimed to analyse the genetic polymorphisms of β-casein in Chinese Holstein cows. β-casein has received considerable research interest in the dairy industry and animal breeding in recent years as a source not only of high quality protein, but also of bioactive peptides that may be linked to health effects. Morever, the polymorphic nature of β-casein and its association with milk production traits, composition, and quality also attracted several efforts in evaluating the allelic distribution of β-casein locus as a potential dairy trait marker. However, few data on beta-casein variants are available for the Chinese Holstein cow. In the present paper, one hundred and thirty three Holstein cows were included in the analysis. Results revealed the presence of 5 variants (A1, A2, A3, B and I), preponderance of the genotype A1A2 (0·353) and superiorities of A1/A2 alleles (0·432 and 0·459, respectively) in the population. Sequence analysis of β-casein gene in the cows showed four nucleotide changes in exon 7. Our study can provide reference and guidance for selection for superior milk for industrial applications and crossbreeding and genetic improvement programmes.

We recently reported the identification of a peptide from yoghurts with promising potential for intestinal health: the sequence (94-123) of bovine β-casein. This peptide, composed of 30 amino acid residues, maintains intestinal homoeostasis through production of the secreted mucin MUC2 and of the transmembrane-associated mucin MUC4. Our study aimed to search for the minimal sequence responsible for the biological activity of β-CN(94-123) by using several strategies based on (i) known bioactive peptides encrypted in β-CN(94-123), (ii) in silico prediction of peptides reactivity and (iii) digestion of β-CN(94-123) by enzymes of intestinal brush border membranes. The revealed sequences were tested in vitro on human intestinal mucus-producing HT29-MTX cells. We demonstrated that β-CN(108-113) (an ACE-inhibitory peptide) and β-CN(114-119) (an opioid peptide named neocasomorphin-6) up-regulated MUC4 expression whereas levels of the secreted mucins MUC2 and MUC5AC remained unchanged. The digestion of β-CN(94-123) by intestinal enzymes showed that the peptides β-CN(94-108) and β-CN(117-123) were present throughout 1·5 to 3 h of digestion, respectively. These two peptides raised MUC5AC expression while β-CN(117-123) also induced a decrease in the level of MUC2 mRNA and protein. In addition, this inhibitory effect was reproduced in airway epithelial cells. In conclusion, β-CN(94-123) is a multifunctional molecule but only the sequence of 30 amino acids has a stimulating effect on the production of MUC2, a crucial factor of intestinal protection.

The bovine β-casein (CSN2) gene has been shown to span a region of 8·5 kb, containing nine exons and eight intervening introns (Bonsing et al. 1988; Martin et al. 2002). The exons range in size from 24 to 498 bp; the introns, however, are much larger and account for 85% of the gene. Twelve genetic variants in the coding sequence of the β-casein gene have been reported (Farrell et al. 2004). The A2 allele of the β-casein gene has been associated with a higher milk production (Lin et al. 1986; Bech & Kristiansen, 1990) while the B variant has been associated with an increase in protein content and better cheesemaking properties (Marziali & Ng-Hang-Kwai, 1986). The β-casein gene codes for a protein of 209 amino acids with varying regions at codons 67, 106 and 122. The A1 variant differs from A2 at position 67, where a histidine replaces a proline (Lien et al. 1992). The β-casein A2 variant has histidine and the A3 variant has glycine at position 106 (Lien et al. 1992); the β-casein A2 variant has serine at position 122 and the β-casein B variant has arginine at this codon (Stewart et al. 1987; Damiani et al. 1992).

The goat calcium-sensitive caseins (αs1, β and αs2) represent, over many years, an excellent model for demonstrating that the major part of the variability observed in the content of these proteins in goat milk is mostly due to the presence of autosomal alleles at single structural loci (CSN1S1, CSN2 and CSN1S2 respectively) clustered on a 200 kb segment of chromosome 6; furthermore, CSN1S1 and CSN2 are convergently transcribed and are only 12 kb apart (Rijnkels, 2002).

The impact of dietary components on the immune system is gaining increased attention in the effort to develop safe food products, some even with health-promoting potential, as well as to improve the basic understanding of the immunomodulatory potential of common food components. In such studies, which are mainly based on experiments in vitro, it is important to be able to differentiate nonspecific activation of immune cells induced by dietary components from ex vivo restimulation of antigen-specific cells that might be present in cell cultures owing to prior dietary exposure to the antigens in cell donors. Focusing on the immunostimulatory potential of cows' milk proteins and peptides, we studied the impact of prior dietary exposure to cows' milk on proliferation of murine immune cells upon ex vivo stimulation with bovine milk proteins. Nonspecific proliferation induced by β-casein peptides was further assessed on cells from mice bred on a cows'-milk-free diet. Regarding the dietary effect, we found that prior oral intake of cows' milk proteins affected cell proliferation induced by culturing with cows' milk proteins in vitro, as spleen cells from mice fed a milk-containing diet showed a significantly greater proliferative response than did cells from mice bred on a cows'-milk-free diet. Studies of immune enhancing potentials of β-casein peptides showed that some peptides stimulate proliferation of immune cells nonspecifically. In conclusion, these findings stress the importance of employing immune cells from mice unexposed to cows' milk for studies of the immunomodulating capacity of cows' milk proteins and peptides, in order to rule out the interference caused by antigen-specific immune responses. By using such cells, we here show that some β-casein peptides possess the potential to induce proliferation in immune cells in a nonspecific manner.

Proteolysis of casein is the principal cause of textural changes and flavour development in ripened cheese (Fox & McSweeney, 1996). Caseins are degraded into small peptides and free amino acids during a complex process, described by Grappin et al. (1985) as a two-step scheme. Caseins are initially broken down into large, well characterised fragments. This initial step, called primary proteolysis, is catalysed principally by the residual coagulant (chymosin and pepsin), and to a variable extent by endogenous milk proteases, such as plasmin, cathepsin D, and possibly somatic cell proteinases. Enzymes originating from either rennet or milk are active in most ripened cheese varieties. However, their relative contributions vary substantially depending on manufacturing practices. For instance, in Swiss-type cheeses, cooking the curd extensively inactivates the coagulant, and simultaneously enhances plasmin activity, which therefore becomes predominant (Ollikainen & Kivela, 1989).