Occurence of beta-casomorphins 5 and 7 in commercial dairy products and in their digests following in vitro simulated gastro-intestinal digestion

The occurrence of b-casomorphin-5 (BCM5) and b-casomorphin-7 (BCM7) was investigated in commercial dairy products and in their digests, following in vitro simulated gastro-intestinal digestion (SGID), by means of HPLC–MS. The analysed dairy products were as follows: 10 cheeses (Gorgonzola, Caprino, Brie, Taleggio, Gouda, Fontina, Cheddar and Grana Padano 10-, 15- or 25-m ripened); 4 samples of drinking milk (unprocessed, pasteurised, UHT and in bottle-sterilised); 2 yoghurts and 4 fermented milks containing probiotics; 7 infant formulas; and 4 dried milk-derivatives (skim milk powder, calcium caseinate and milk protein concentrates). b-Casomorphin-5 was not detected in dairy products, either prior to or after SGID. b-Casomorphin-7 was detected only in cheeses with the exception of Taleggio, Caprino and Grana Padano samples. Peptide amount was in the range 0.01–0.15 mg kg-1 the highest level being recovered in Brie sample. Following SGID, BCM7 formed in all dairy samples or increased up to 21.77 mg kg-1 in digests of cheeses. The peptide level ranged from 0.29 to 1.23 mg kg-1 in fermented milks and from 3.46 to 22.18 mg kg-1 in dried milk-derivatives. Digests of commercial infant formulas contained BCM7 at concentrations of 0.04–0.21 mg l-1. For the first time, this work reports quantitative values for BCM5 and BCM7 in a range of dairy products providing evidence that, during processing, only proteolytic systems involved in manufacturing and ripening of cheese can potentially hydrolyse b-CN to BCM7. Nevertheless, formation or further release of BCM7 is mainly promoted by the action of gastrointestinal proteinases during in vitro digestion irrespective of the type of dairy product.