A comparison of the in vitro ACE inhibitory capacity of dairy and plant proteins

Bovine milk proteins and their peptides have been shown to exert Angiotensin-Converting Enzyme inhibitory (ACEi) activity in vivo and in vitro, after gastro-intestinal digestion. To gain insight into dairy proteins digestion pattern and bioactive potential, a set of dairy proteins consisting of a range of casein and whey-based products and plant proteins including those derived from soya, peas and wheat was sequentially hydrolysed in simulated human physiological conditions. The total digesta was filtered using 3kDa membrane, in order to mimic the intestinal absorption. A permeate (absorbed fraction) and a retentate (intestinal fraction) were obtained. ACEi activity was measured as the ability of protein fractions (pre-digested, gastric, permeate and retentate) to decrease the hydrolysis of furanacroloyl-Phe-Glu-Glu (FAPGG) synthetic substrate for ACE enzyme. Results showed that permeate and retentate of dairy proteins exerted a significant ACEi activity (27.05 \ub1 2.99%; P< 0.05) compared with the pre-digested dairy proteins (16.26 \ub1 1.53%). In particular, among dairy proteins tested, permeate of whey protein isolate and whey protein hydrolysed samples showed the highest ACEi capacity. Conversely, an opposite trend was observed for plant proteins. Plant protein permeate exhibited the lowest ACEi activity (16.52 \ub1 2.92%), compared with the all the other fractions. The ACEi results support the growing evidence that bioactive peptides within dairy and plant proteins are encrypted in an inactive form within parent protein sequences with hydrolysis needed for activity to be realized. The comparison of the in vitro effect of dairy and plant proteins performed in this study could provide valuable knowledge regarding their different bioactivities, promoting their use in the formulation of functional foods