Upgrading collagenous smooth hound by-products: Effect of hydrolysis conditions, in vitro gastrointestinal digestion and encapsulation on bioactive properties

Abstract

Collagenous by-products derived from smooth hound (Mustelus mustelus) were studied using trypsin hydrolysis to obtain protein hydrolysates with ACE (angiotensin converting enzyme) and/or PEP (prolyl endopeptidase)-inhibitory activities. Most of the hydrolysates were mainly composed of short peptides. A response surface methodology (RSM) was used to optimize the conditions of hydrolysis (pH 7, 8 or 9, and temperatures of 35, 45 or 55ºC), which led to a higher degree of hydrolysis (DH=3.4%), as well as to an increase in ACE and PEP-inhibitory activities (maximal inhibitions of 68.1 and 81.7%, respectively). According to the model used, neither hydrolysis temperature nor pH in the ranges studied had a significant effect on DH, whereas PEP-inhibitory activity was significantly affected by both factors. pH had a significant effect on ACE-inhibitory activity. Optimum conditions of hydrolysis to obtain maximum activity differed for the two activities: 35ºC/pH 7 for PEP-inhibitory activity and 45.9ºC/pH 9 for ACE-inhibitory activity. The results suggested that these biological activities were influenced by peptide sequence rather than peptide length. This was also confirmed by the amino acid composition and molecular weight (MW) profiles. The ACE-inhibitory activity of the most potent hydrolysate was evaluated after in vitro gastrointestinal digestion. The results showed a worsening of the activity, which was related to small peptide losses and to the appearance of new low MW peptides.Hydrolysate encapsulation using an alginate-whey protein isolate microsphere improved the ACE-inhibitory activity (IC50=0.24 mg/ml).