Hexose, sialic acid and sialyllactose concentrations in the milk of dairy and non-dairy breed cows

It has been suggested that the ratio of lactose to milk oligosaccharides in mammalian milk/colostrum is based on the ratio of expression of a-lactalbumin and glycosyltransferases in the mammary epithelial cells. It has also been suggested that the high secretion of milk in dairy breed cows has been acquired by a high expression of a-lactalbumin expression. As there is a large difference of milk secretion level between dairy and non dairy breed cows, there may be a difference in the ratio of lactose to milk oligosaccharides in milks between dairy and non dairy breed cows. In this study, the concentrations of hexose, sialic acid as well as sialyllactoses, which are representative bovine milk oligosaccharides, were determined in the milks of dairy and non dairy breed cows. The concentration of hexose was significantly higher in the milks of non dairy breed cows than that of dairy breed cows, but there were no significant differences with respect to sialic acid and sialyllactose. The significant difference of the ratio of the concentrations of 3'- and 6'-sialyllactose to total hexose in milk was not observed between dairy and non dairy cows.

DNA-based analysis of protein variants reveals different genetic variability of the paralogous equine ß-lactoglobulin genes LGB1 and LGB2

The genetic variability of milk protein genes may influence the nutritive value or processing and functional properties of the milk. While numerous protein variants are known in ruminants, knowledge about milk protein variability in horses is still limited. Mare's milk is, however, produced for human consumption in many countries. Beta-lactoglobulin belonging to the protein family of lipocalins, which are known as common food- and airborne allergens, is a major whey protein. It is absent from human milk and thus a key agent in provoking cow's milk protein allergy. Mare's milk is, however, usually better tolerated by most affected people. Several functions of β-lactoglobulin have been discussed, but its ultimate physiological role remains unclear. In the current study, the open reading frames of the two equine β-lactoglobulin paralogues LGB1 and LGB2 were re-sequenced in 249 horses belonging to 14 different breeds in order to predict the existence of protein variants at the DNA-level. Thereby, only a single signal peptide variant of LGB1, but 10 different putative protein variants of LGB2 were identified. In horses, both genes are expressed and in such this is a striking previously unknown difference in genetic variability between the two genes. It can be assumed that LGB1 is the ancestral paralogue, which has an essential function causing a high selection pressure. As horses have very low milk fat content this unknown function might well be related to vitamin-uptake. Further studies are, however, needed, to elucidate the properties of the different gene products.

Evidence of native starch degradation with human small intestinal maltase-glucoamylase (recombinant)

Action of human small intestinal brush border carbohydrate digesting enzymes is thought to involve only final hydrolysis reactions of oligosaccharides to monosaccharides. In vitro starch digestibility assays use fungal amyloglucosidase to provide this function. In this study, recombinant N-terminal subunit enzyme of human small intestinal maltase-glucoamylase (rhMGAM-N) was used to explore digestion of native starches from different botanical sources. The susceptibilities to enzyme hydrolysis varied among the starches. The rate and extent of hydrolysis of amylomaize-5 and amylomaize-7 into glucose were greater than for other starches. Such was not observed with fungal amyloglucosidase or pancreatic alpha-amylase. The degradation of native starch granules showed a surface furrowed pattern in random, radial, or tree-like arrangements that differed substantially from the erosion patterns of amyloglucosidase or alpha-amylase. The evidence of raw starch granule degradation with rhMGAM-N indicates that pancreatic alpha-amylase hydrolysis is not a requirement for native starch digestion in the human small intestine.

Human intestinal maltase-glucoamylase: crystal structure of the N-terminal catalytic subunit and basis of inhibition and substrate specificity

Human maltase-glucoamylase (MGAM) is one of the two enzymes responsible for catalyzing the last glucose-releasing step in starch digestion. MGAM is anchored to the small-intestinal brush-border epithelial cells and contains two homologous glycosyl hydrolase family 31 catalytic subunits: an N-terminal subunit (NtMGAM) found near the membrane-bound end and a C-terminal luminal subunit (CtMGAM). In this study, we report the crystal structure of the human NtMGAM subunit in its apo form (to 2.0 A) and in complex with acarbose (to 1.9 A). Structural analysis of the NtMGAM-acarbose complex reveals that acarbose is bound to the NtMGAM active site primarily through side-chain interactions with its acarvosine unit, and almost no interactions are made with its glycone rings. These observations, along with results from kinetic studies, suggest that the NtMGAM active site contains two primary sugar subsites and that NtMGAM and CtMGAM differ in their substrate specificities despite their structural relationship. Additional sequence analysis of the CtMGAM subunit suggests several features that could explain the higher affinity of the CtMGAM subunit for longer maltose oligosaccharides. The results provide a structural basis for the complementary roles of these glycosyl hydrolase family 31 subunits in the bioprocessing of complex starch structures into glucose.

Cholesterol transporters in lactating and nonlactating human mammary tissue

In mammals milk is the principal nutrient for neonates at birth. The basic milk composition is similar between different mammals, but the content of individual constituents such as lipids may differ significantly from one species to another. The milk fat fraction is mainly composed of triglycerides which account for more than 95% of the lipids found in human and bovine milk. Though sterols and in particular cholesterol, the predominant milk sterol, represent less than 0.5% of the total milk lipid fraction, they are of ultimate importance for biological processes such as the formation of biological membranes or as precursors for steroid hormone synthesis. Cholesterol found in milk originates either from blood uptake or from local synthesis. This chapter provides an overview of cholesterol exchanges between the blood, the mammary tissue and the milk. The current knowledge on the expression, localization and function of candidate cholesterol transporters in mammary tissues of human, murine and bovine origin is summarized. Different mechanisms of how cholesterol can be transferred via the mammary tissue into milk, and which active cholesterol transporters are likely to play a role in this process will be discussed.

Antimicrobial susceptibility of gram-positive udder pathogens from bovine mastitis milk in Switzerland

We evaluated the susceptibility of the gram-positive mastitis pathogens S. aureus, Str. uberis, Str. dysgalactiae, E. faecalis and L. garviae to antibiotics that are of epidemiological interest or are critically important for mastitis therapy and human medicine. Penicillin resistance was found to be most frequent in S. aureus, and nearly 5 % of the Str. uberis strains displayed a decreased susceptibility to this antibiotic. Resistance to aminoglycosides and macrolides was also detected in the strains tested. The detection of methicillin-resistant S. aureus (MRSA) and of a ciprofloxacin-resistant Str. dysgalactiae isolate corroborated the emergence of mastitis pathogens resistant to critically important antibiotics and underscores the importance of susceptibility testing prior to antibiotic therapy. The monitoring of antibiotic susceptibility patterns and antibiogram analyses are strongly recommended for targeted antimicrobial treatment and to avoid the unnecessary use of the latest generation of antibiotics.

Role of milk and meat products as vehicles for antibiotic-resistant bacteria

This subject is reviewed under the following headings: Microbial contamination of raw meat and raw milk; Antibiotic resistance of food-borne pathogens; Antibiotic resistance of commensal and potentially pathogenic bacteria as a new threat in food microbiology; Antibiotic-resistant staphylococci in fermented meat and [in] milk products; Antibiotic-resistant Enterococcus sp. in fermented meat and [in] milk products; Enterococci in farm animals and meat; Enterococci in fermented food; Molecular characterization of resistance of food-borne enterococci; and Further ecological and epidemiological considerations of resistant live bacteria in food. It is concluded that further research is needed, particularly into the possible transfer of the resistance of bacteria consumed in meat or milk products to the indigenous bacteria of the human consumer.