Caseinomacropeptide (CMP) is derived from the chymosin cleavage of κ-casein during cheese production. This study developed gels from CMPs, which were isolated by different ultrafiltration systems, and whey protein isolate (WPI), and studied their rheological and ultrastructural characteristics. The 30% WPI gel showed high elastic modulus (G′) values and stronger structure than the other samples with CMP. Another gel, with 50% protein, 30% WPI and 20% CMP sample isolated from the 30 kDa retentate, had a weaker structure and lower G′ value. The third gel, with 30% WPI and 20% CMP sample from the 5 kDa retentate derived from the 30 kDa retentate, presented intermediate structural strength. Despite the increase in protein concentration from the addition of CMP, there was a decrease in the strength of the gel network. Different CMP isolation processes also contributed to differences in the microscopic analysis of gel structures with the same protein content.

Bovine κ-casein glycomacropeptide (GMP) is a sialic acid containing glycopeptide having many biological activities. The study described in this research communication was undertaken to determine whether sialic acid rich glycopeptide can be produced from GMP by proteinase treatment. A sample of GMP was hydrolyzed with papain, and the obtained hydrolysate was chromatographed on a column of diethylaminoethyl-Sephacel to obtain a glycopeptide fraction (GPF). This product accounted for average 48.1% dry weight of GMP or 81.1% total recovered sialic acid from GMP. The content of sialic acid (expressed as % dry weight) was 1.7 times higher in GPF (22.6) than in unhydrolyzed GMP (13.4). Major differences in amino acid composition between GPF and GMP were found in the contents (mol%) of: lysine (<1 and 4.5, respectively), serine (20.3 and 10.3, approximately twice higher in GPF), asparagine/aspartic acid and isoleucine. The contents of the last two amino acids were approximately twice lower in GPF. On gel filtration chromatography with Sephacryl S-100, GMP was eluted as a single peak with elution volume similar to that of dimeric β-lactoglobulin (36.6 kDa) whereas GPF was eluted in two peaks both with elution volumes greater than that of α-lactalbumin (14.2 kDa). These peak fractions containing high (fraction I) and low (fraction II) molecular size glycopeptides gave different sialic acid to peptide ratio, which was 1.7 times higher in fraction I than in fraction II. Results of size exclusion HPLC on Superdex-75 were consistent with those of gel filtlation chromatography. On cellulose acetate electrophoresis, the mobility of GPF relative to that of GMP as 1.0 was found to average 1.2, suggesting a higher negative charge density in GPF than in GMP. It was concluded that papain digestion of GMP is an efficient method to produce glycopeptide with high sialic acid content.

Bovine κ-casein glycomacropeptide (GMP) found in cheese whey is a sialylated phosphorylated peptide which is thought to be a potential ingredient for functional food as well as dietetic food. This study was undertaken to determine whether high purity GMP can be isolated from soluble whey fraction (SWF) using column chromatography on food grade anion exchange resin and chitin as an adsorbent. Samples of commercially available anion exchange resin (resin A, resin B and resin C) and those of chitin (chitin A, chitin B and chitin C) were examined in this experiment. The GMP fraction obtained from each column was analyzed for amino acid composition which reflects the purity of the peptide. Major findings for commercial anion exchange resin were that: (1) the proportion of GMP monitored as sialic acid in total recovered sialic acid was similar among the three samples of resin accounting for average 78% of recovered sialic acid; (2) the GMP fraction from resin A or resin B contained undetectable level of contaminating amino acids including phenylalanine, histidine, arginine and tyrosine; (3) the GMP fraction from resin C contained small amounts (<1 mol%) of contaminating amino acids, arginine, phenylalanine and tyrosine; and (4) the GMP binding capacity expressed as mg/100 mg dry weight of resin was more than 2.5 times higher in resin C (average 22.9) than in resin A or resin B with no difference between resin A and resin B averaging 8.7. Results obtained for chitin A, chitin B and chitin C were in general similar to those found with resin A and resin B. Since chitin has a remarkable GMP binding capacity averaging 8.6 mg/100 mg dry weight of chitin, it may be a useful adsorbent for whey fractionation. Further research is needed to develop an efficient inexpensive method to purify GMP.

Bovine κ-casein glycomacropeptide (GMP) found in sweet whey is a 64 amino acid residue glycopeptide, which does not contain phenylalanine or other aromatic amino acids. There is, however, little information available concerning isolation of phenylalanine free GMP from sweet whey. In the study reported in this Research Communication, GMP was purified from three samples of sweet whey protein products (SWPP) by a procedure involving: (1) precipitation of protein by heat treatment; (2) precipitation of protein by pH shift to 4·6; and (3) diethylaminoethyl (DEAE)-Sephacel anion exchange chromatography of soluble portion of each sample obtained after removal of protein precipitates. The total protein precipitated with both heat treatment and pH shift accounted for average 61% of dry weight of SWPP. The GMP fraction obtained by DEAE-Sephacel chromatography accounted for average 7·5% of dry weight of SWPP. Amino acid analysis showed that there was no detectable level of phenylalanine in GMP fractions from all samples examined. The present method may help develop large scale methods of production of GMP.

Milk protein-derived peptides have been reported to have potential benefits for reducing the risk of type 2 diabetes. However, what the active components are and whether intact peptides exert this bioactivity has received little investigation in human subjects. Furthermore, potentially useful bioactive peptides can be limited by low bioavailability. Various peptides have been identified in the gastrointestinal tract and bloodstream after milk-protein ingestion, providing valuable insights into their potential bioavailability. However, these studies are currently limited and the structure and sequence of milk peptides exerting bioactivity for glycaemic management has received little investigation in human subjects. The present article reviews the bioavailability of milk protein-derived peptides in human studies to date, and examines the evidence on milk proteins and glycaemic management, including potential mechanisms of action. Areas in need of advancement are identified. Only by establishing the bioavailability of milk protein-derived peptides, the active components and the mechanistic pathways involved can the benefits of milk proteins for the prevention or management of type 2 diabetes be fully realised in future.

Probiotic Lactobacillus and Bifidobacterium species are generally fastidious bacteria and require rich media for propagation. In milk-based media, they grow poorly, and nitrogen supplementation is required to produce high bacterial biomass levels. It has been reported that caseinomacropeptide (CMP), a 7-kDa peptide released from κ-casein during renneting or gastric digestion, exhibits some growth-promoting activity for lactobacilli and bifidobacteria. During the digestive process, peptides derived from CMP are detected in the intestinal lumen The aim of this study was to evaluate the effects of peptic and tryptic digests of CMP on probiotic lactic acid bacteria growth in de Man, Rogosa and Sharpe broth (MRS) and in milk during fermentation at 37 °C under anaerobic conditions. The study showed that pepsin-treated CMP used as supplements at 0·5 g/l can promote the growth of probiotics even in peptone-rich environments such as MRS. The effect was strain-dependent and evident for the strains that grow poorly in MRS, with an improvement of >1·5 times (P<0·05) by addition of pepsin-treated CMP. Trypsin-treated CMP was much less efficient as growth promoter. Moreover, pepsin-treated CMP was effective in promoting the growth in milk of all probiotic lactic acid bacteria tested, with biomass levels being improved significantly, by 1·7 to 2·6 times (P<0·05), depending on the strain. Thus, supplementation of MRS and of milk with pepsin-treated CMP would be advantageous for the production of high biomass levels for Bifidobacteria and Lactobacilli.

This work studied the behaviour of caseinomacropeptide (CMP) in a whey protein fractionation process based on the selective precipitation of α-lactalbumin (α-la) in an acid medium. Three different acids (hydrochloric, citric and lactic) and different operating conditions (protein concentration, temperature and pH) were considered to perform the precipitation step. Under the optimised precipitation conditions obtained for α-la (pH 4, 55°C, initial α-la concentration around 12 g/l) CMP presents quite similar behaviour to that observed for β-lactoglobulin (β-lg), namely remaining in the supernatant fraction. However, at a lower pH value (3·5) the amount of precipitated CMP increases up to 72% when citric acid is added. This behaviour could be due to the fact that CMP is close to its isoelectric point, which allows a supernatant fraction enriched in β-lg that is almost free from the rest of proteins in sweet whey.