β-CN-5P and β-CN-4P components of bovine milk proteose–peptone: Large scale preparation and influence on the growth of cariogenic microorganisms

Abstract

Indigenous proteolytic activity in milk, mostly due to plasmin, gives rise to many casein-derived peptides that subsequently are found in the proteose–peptone fraction of milk where they comprise 10% or more of the total whey protein. Prominent amongst proteose–peptone components are β-CN-5P (β-casein residues, 1–105/107) and β-CN-4P (β-casein residues 1–28). Many peptides have potentially valuable functional or biological properties that differ from those of the parent proteins, and this paper describes simple, rapid and cost-effective preparation of these two milk peptide components in a high degree of purity, and in gramme quantities, for evaluation of such properties. The purification process was more efficient if β-casein was used as starting material. In this work, we prepared 46 g of β-casein from sodium caseinate in a simple rapid DEAE-cellulose ion-exchange chromatography stage. This was followed by in vitro hydrolysis with plasmin and precipitation and gel filtration steps to yield 4.8 g of highly purified β-CN-5P and 1.2 g of β-CN-4P. Utilising either unfractionated sodium caseinate, or milk itself, as starting material was satisfactory but gave less purified material containing other peptide impurities. Peptides similar to these proteose–peptone components have been implicated in the protective effects of milk and dairy products against dental caries in teeth. The mechanism(s) by which this protection occurs is unclear, but some antibiotics are peptides. However, we have found that, even at peptide concentrations as high as 0.5 mg/ml, neither β-CN-5P nor β-CN-4P had any effect on the in vitro growth of cariogenic Streptococcus mutans bacteria, ruling out a simple antibiotic mechanism.