Release of beta-casomorphins 5 and 7 during simulated gastro-intestinal digestion of bovine beta-casein variants and milk-based infant formulas

The release of beta-casomorphin-5 (BCM5) and beta-casomorphin-7 (BCM7) was investigated during simulated gastro-intestinal digestion (SGID) of bovine b-casein variants (n = 3), commercial milk-based infant formulas (n = 6) and experimental infant formulas (n = 3). SGID included pepsin digestion at pH 2.0, 3.0 and 4.0 and further hydrolysis with Corolase PPTM. beta-Casein (b-CN) variants were extracted from raw milks coming from cows of Holstein-Friesian and Jersey breeds. Genomic DNA was isolated from milk and the b-CN genotype was determined by a PCR-based method. Phenotype at protein level was determined by capillary zone electrophoresis in order to ascertain the level of gene expression. Recognition and quantification of BCMs involved HPLC coupled to tandem MS. Regardless of the pH, BCM7 generated from variants A1 and B of b-CN (5–176 mmol/mol casein) the highest amount being released during SGID of form B. As expected, the peptide was not released from variant A2 at any steps of SGID. BCM5 was not formed in hydrolysates irrespective of either the genetic variant or the pH value during SGID. Variants A1, A2 and B of b-CN were present in all the commercial infant formulae (IFs) submitted to SGID. Accordingly, 16–297 nmol BCM7 were released from 800 ml IF, i.e. the daily recommended intake for infant. Industrial indirect-UHT treatments (156 °C x 6–9 s) did not modify release of BCM7 and, during SGID, comparable peptide amounts formed in raw formulation and final heat-treated IFs.