ANGIOTENSIN-I-CONVERTING ENZYME INHIBITORY AND ANTIOXIDANT ACTIVITY OF TRYPTIC SPIRULINA PLATENSIS PROTEIN HYDROLYSATES: EFFECT OF HYDROLYSIS AND IN VITRO GASTROINTESTINAL DIGESTION

In this study, protein hydrolysates derived from  Spirulina platensis  protein (SPPHs) using trypsin were investigated in terms of angiotensin I-converting enzyme (ACE) inhibitory activity, antioxidant activity and total phenolic content (TPC) and subjected to an  in vitro  digestion model using human gastric and duodenal fluids. Moreover, the effects of hydrolysis time and enzyme/substrate (E/S) ratio on the degree of hydrolysis (DH) of the hydrolysates were determined. The maximum DH (%) was found as 25.03±0.89% with the combination of E/S ratio of 3:100, hydrolysis time of 8 hours (p<0.05). The highest ACE inhibitory activity value was observed as 21.79±1.52% for initial SPPHs, prepared within the hydrolysis conditions of E/S ratio of 3:100 and hydrolysis time of 8 h. In general, the increase in E/S ratio and hydrolysis time resulted in an increase in the DH and in an improved ACE inhibitory activity of both initial and the GI digested samples (p<0.05). After digestion by pepsin, TPC of the digests was in the range of 28.87±0.32 and 40.28±1.05mg caffeic acid equivalent/g dry weight. However, further digestion by pancreatin led TPC of the final GI digest between 19.85±1.24 and 29.00±1.00mg caffeic acid equivalent/g dry weight. Moreover, the antioxidant activity of further digested SPPHs by gastric and intestinal proteases remained generally stable after  in vitro  treatment.