Levels Of Α-lactalbumin Research Articles

How α -lactalbumin and β –casein level in infant formula influence the protein and minerals absorption properties by using Caco-2 cell model

This study investigated the differences in absorption of infant formula with different levels of α-lactalbumin (α-La) and β-casein (β-CN), and how α-La and β-CN (α+β) affect mineral absorption using the Caco-2 cell model. Compared to the control group, the free amino acid content transported to the basal side significantly increased in the fortification of α-La and β-CN, particularly in the α+β (high) group, which reached 11.343 μmol/L. Furthermore, fortification of α-La and β-CN upregulated the expression of the amino acid transporter SLC6A14 and the oligopeptide transporter PEPT1, in particular the expression of SLC6A14 in the α+β (high) group was 103% of that of the control group. In addition, fortification of α-La and β-CN enhanced the absorption of Ca, Mg, and Zn. The absorption rates of Ca, Mg, and Zn in α+β (high) group increased to 31.27%, 13.66%, and 58.59%, respectively, of which α-La contributed the most on Ca absorption. In conclusion, α-La and β-CN fortification not only increased the absorption of amino acids and peptides but also promoted the absorption of minerals, which provide evidence for the benefits of adjustment of α-La and β-CN in the infant formula.

Longitudinal changes in the bioactive proteins in human milk of the Chinese population: A systematic review.

This systematic review aimed at investigating longitudinal changes in human milk bioactive protein concentrations in Chinese population. Both English and Chinese databases were searched. The data were pooled into six defined lactation stages. Weighted means of protein concentrations in each stage and the statistical significance of means of different lactation stages were calculated. The data of 11 bioactive proteins were retrieved. Concentrations of sIgA, IgM, and IgG decreased sharply during the first 14 days of lactation. The levels of α‐lactalbumin, lactoferrin, and β‐casein also decreased throughout lactation. Conversely, lysozyme levels increased over lactation. The changing patterns of the serum albumin, osteopontin, and bile salt‐stimulated lipase (BSSL) were not conclusive. This study represents the most comprehensive summary of bioactive proteins in Chinese human milk. In the future, mass spectrometry‐based analysis of human milk proteomics may be used to investigate the longitudinal changes of many more bioactive proteins.

Effect of pH on heat stability of yak milk protein

Heat stability of yak milk protein reached a maximum at approximately pH 6.8 and was low at pH < 6.4 and pH > 7.0. At pH 6.4, the particle size of yak milk increased by approximately 20 and 25 nm when heated at 140 °C for 2 min and 120 °C for 10 min, respectively. The particle size of heated yak milk decreased markedly with increasing pH. The content of κ-casein dissociated from the casein micelles increased from 5.7% to 9.5% at pH 6.4–76.3% and 81.5% at pH 7.2 when yak milk was heated at 140 °C for 2 min and 120 °C for 10 min, respectively. The proteins αS1-casein and β-casein showed a much lesser extent of dissociation from the micelles than did κ-casein. The levels of α-lactalbumin and β-lactoglobulin in ultracentrifugal supernatants increased from pH 6.4 to pH 7.2 and decreased above pH 7.2.

Mammary cell activity and turnover in dairy cows treated with the prolactin-release inhibitor quinagolide and milked once daily

To assess the regulation of mammary cell activity, survival, and proliferation by prolactin (PRL), 5 Holstein cows in early lactation received daily i.m. injections of 1mg of quinagolide, a suppressor of PRL release, for 9 wk, whereas 4 control cows received the vehicle (water) only. During the last week of treatment, one udder half was milked once a day (1×) and the other twice a day (2×). Mammary biopsies were harvested 1 wk before and 4 and 8 wk after the start of quinagolide treatment. The quinagolide injections reduced milk yield and resulted in lower levels of κ-casein and α-lactalbumin mRNA in the mammary biopsies at wk 4 compared with the control cows. In the mammary tissue of the quinagolide-treated cows at wk 8 of treatment, cell proliferation (as determined by proliferating cell nuclear antigen labeling) was lower and apoptosis (as determined by the terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling assay) was higher than in the mammary tissue of the control cows. During differential milking, mammary epithelial cells (MEC) were extracted from the milk by centrifugation and purified by immunocytochemical binding to allow variations in the levels of mammary transcripts to be observed. After 9 wk of treatment, levels of α-lactalbumin and κ-casein mRNA were lower in the MEC isolated from milk of the quinagolide-treated cows. This effect was associated with lower PRL receptor mRNA levels and a tendency toward lower viability in the milk-isolated MEC from the 2×-milked glands. The decrease from 2× milking to 1× milking also downregulated α-lactalbumin and κ-casein transcripts in the milk-isolated MEC. Viability was higher for the MEC collected from the 1×-milked udder halves compared with the 2×-milked halves. In conclusion, the reduction in milk yield after chronic administration of the PRL-release inhibitor quinagolide is associated with a reduction in mammary cell activity, survival, and proliferation in lactating dairy cows. Reduced milking frequency was also associated with a decrease in MEC activity.

Preparation of ingredients containing an ACE-inhibitory peptide by tryptic hydrolysis of whey protein concentrates

This study describes the characterisation of whey protein hydrolysates obtained from tryptic hydrolysis to assess their application as ingredients with angiotensin-converting-enzyme (ACE) inhibitory action. The levels of α-lactalbumin ( α-la) and β-lactoglobulin ( β-lg) remaining after hydrolysis were quantified. Peptides were separated by RP-HPLC, and Ala-Leu-Pro-Met-His-Ile-Arg (ALPMHIR), the most potent β-lg-derived ACE-inhibitory peptide was monitored. A correlation curve was established for the production of this peptide as a function of hydrolysis time. Heat-induced gelation of hydrolysates was studied by small-deformation rheology. The gelation times and the strength of the final gels were highly dependent on the degree of hydrolysis. Smaller peptides liberated by hydrolysis contributed to the inability of whey protein hydrolysates to gel.

Secretion of whey acidic protein and cystatin is down regulated at mid-lactation in the red kangaroo ( Macropus rufus)

Milk collected from the red kangaroo ( Macropus rufus) between day 100 and 260 of lactation showed major changes in milk composition at around day 200 of lactation, the time at which the pouch young begins to temporarily exit the pouch and eat herbage. The carbohydrate content of milk declined abruptly at this time and although there was only a small increase in total protein content, SDS PAGE analysis of milk revealed asynchrony in the secretory pattern of individual proteins. The levels of α-lactalbumin, β-lactoglobulin, serum albumin and transferrin remain unchanged during lactation. In contrast, the protease inhibitor cystatin, and the putative protease inhibitor whey acidic protein (WAP) first appeared in milk at elevated concentrations after approximately 150 days of lactation and then ceased to be secreted at approximately 200 days. In addition, a major whey protein, late lactation protein, was first detected in milk around the time whey acidic protein and cystatin cease to be secreted and was present at least until day 260 of lactation. The co-ordinated, but asynchronous secretion of putative protease inhibitors in milk may have several roles during lactation including tissue remodelling in the mammary gland and protecting specific proteins in milk required for physiological development of the dependent young.

Effect of decreased milking frequency of cows in late lactation on milk somatic cell count, polymorphonuclear leucocyte numbers, composition and proteolytic activity.

The effects of reducing the frequency of milking of cows in late lactation on milk somatic cell count (SCC), polymorphonuclear leucocyte (PMN) content, chemical composition and proteolytic activity were investigated. Intermittent milking is frequently practised by Irish farmers in late lactation, and the objective of this study was to determine whether this procedure could be linked to altered quality of milk. Seventeen Holstein Friesian cows in late lactation (> 215 d in milk) were assigned to two treatment groups, and were either milked twice a day until drying-off (control group) or milked intermittently as the yield fell (test group). Milk composition and enzymic characteristics were measured on two occasions. At the first sampling, day 7, test cows were on once daily milking and at the second, day 15, the test cows were being milked every second day. Milk yields were significantly lower in test than control animals and decreased between days 7 and 15 in both groups. Milk SCC and PMN levels were increased on reducing milking frequency and, at day 15, the increase was not linked to decreased milk yield. Milk lactose levels were significantly decreased and pH, alpha-lactalbumin levels, plasmin activity and plasminogen activity significantly increased by reducing milking frequency. In conclusion, reduced frequency of milking in late lactation leads to the production of milk that is abnormal in character and this may be linked to reduced quality of dairy products manufactured from such milk.

Lactose synthetase activities in rat and mouse mammary glands

The activities of lactose synthetase (in the presence and absence of α-lactalbumin), galactosyltransferase and α-lactalbumin levels were determined in rat and mouse mammary glands during pregnancy, lactation and involution. In the rat, essentially none of the above activities were detected prior to parturition. This was followed by a sharp increase with the maximum occurring during late lactation and then by a rapid drop during involution. In the mouse, detectable levels of all the activities occurred at 15 days of pregnancy and these levels increased during pregnancy and reached a maximum level during early lactation and again sharp decreases occurred during involution. The study shows that mammary gland development occurs at an earlier date in the mouse than in the rat.

Lactose synthetase activity of α-lactalbumins from several species

The kinetics of the interaction of the A and B proteins of lactose synthetase was studied and found to conform to simple Langmuir adsorption theory. The affinity of the B proteins of six species for bovine A protein was measured, and the range of affinities was found to differ among species. Taking these factors into consideration, a procedure for utilizing the lactose synthetase reaction as the basis of a functional assay for α-lactalbumin is outlined. Finally, preliminary evidence for a correlation between lactose levels and α-lactalbumin levels in the milks of different species is presented.