Abstract
Variation between bovine A1-or A2-type β-caseins are suggested to affect beta-casomorphin-7 (BCM-7) formation, which may affect health. Studies assessing BCM-7 formation often use raw milk, but processing of milk is known to affect digestion. Using in vitro digestion and stable-isotope assisted peptide quantification, we reveal that BCM-7 is formed under intestinal conditions from both A1-and A2-type milk. Moreover, formation of BCM-7 was affected by industrial relevant heating in both A1 and A2 milk. Further studies with a large number of single A1-and A2-type cows are needed to elaborate if amounts of BCM-7 formed are different between A1 and A2 milk. Both longer and shorter BCM peptide sequences that may display similar activities should be taking into account as a longer BCM-7 containing peptide (BCM-7 +2) could also be detected in A2 milk intestinal digesta.
Highlights
Different genetic variants of b-casein in bovine milk have been postulated to affect health outcomes differentially (Bell, Grochoski, & Clarke, 2006; Brooke-Taylor, Dwyer, Woodford, & Kost, 2017; Küllenberg de Gaudry et al, 2019)
Milk from 6 previously genotyped b-casein A1-type and from 6 b-casein A2-type Holstein-Friesian cows collected from a single herd was blended together to form representative A1-type and A2type milk samples, respectively, and to control for possible cow-tocow difference as observed in previous studies assessing the formation of BCM-7 from single cows (Cieslinska et al, 2007; Nguyen et al, 2021)
Simulated in vitro digestion of milk and direct stable isotopelabel assisted peptide quantification reveals that BCM-7 can be formed from both A1 and A2 milk
Summary
Different genetic variants of b-casein in bovine milk have been postulated to affect health outcomes differentially (Bell, Grochoski, & Clarke, 2006; Brooke-Taylor, Dwyer, Woodford, & Kost, 2017; Küllenberg de Gaudry et al, 2019). Since the 1970s, an opioid-like activity has been assigned to milk, to a casein digest fraction (Teschemacher, Brantl, & Haarmann, 1978) Both in vitro and in vivo studies localised this activity to the N-terminal region of b-casein containing the BCM-7 sequence from which several bioactive sequences with different activities can be formed (Teschemacher et al, 1978; Thiruvengadam, Venkidasamy, Thirupathi, Chung, & Subramanian, 2021). Samples for peptide quantification were taken upon completion of the gastric phase by applying Pepstatin A (SigmaeAldrich) to stop the enzymatic reactions and after completing simulated intestinal digestion by applying Pefabloc (SigmaeAldrich) to stop the enzymatic reactions
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