β-casomorphin 7 (BCM7) is a bioactive peptide that is released during the digestion of some β-casein variants (A1 and B) present in cow’s milk. BCM7 has been linked to several health concerns such as gastrointestinal disorders. Thermal processing alters the composition of milk which in turn may affect its digestion thus affecting the amount of BCM7 that is released. Although filtered milk (this milk undergoes microfiltration and pasteurisation) is widely available from many UK retailers, there is no information about the effect of microfiltration on the release of this peptide. Most of the reported BCM7 quantification studies were based on isolated casein as opposed to whole milk and hence may not accurately represent commercially processed milk. When studying BCM7 formation in commercial milk, limiting protein purification before digestion is ideal as separating milk protein fractions may result in the loss of β-casein in the whey fraction.

This study aimed to understand the impact of microfiltration on BCM7 release after in vitro digestion (mimicking in vivo digestion) of semi-skimmed filtered milk compared to pasteurised milk and pasteurised Jersey milk (which does not contain A1 β-casein, the main source of BCM7). BCM7 peptide was quantified by LC/MS.

Results indicated that the β-casein variants present in milk rather than the milk treatments themselves are the key factors for the release of BCM7. Similar BCM7 levels were found in filtered and pasteurised milk samples, whereas Jersey milk released just half the amount.