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Evaluation of angiotensin I-converting enzyme inhibitory activity after in vitro digestion of soy protein isolate

University of British Columbia

The generation of angiotensin I-converting enzyme (ACE) inhibitory activity in soy protein isolate (SPI) was determined after sequential digestion with pepsin and pancreatin using batch or dynamic model digestion systems. During batch digestion, higher ACE inhibitory activity was measured after the first 40 and 60 minutes of pepsin digestion (E:S = 1:25, pH 2, 37°C) than after subsequent digestion with pancreatin (E:S = 1:25, pH 7.5, 37°C, 120 min). At the end of 180 minutes of batch digestion, IC5 0 values of 0.28 + 0.04, 0.30 + 0.02, and 0.36 ± 0.01 mg/mL were determined for unheated SPI, blanched (100°C, 10 min)-pasteurized (75°C, 15 s) SPI, and blanched (100°C, 10 min)-sterilized (121°C, 20 min) SPI, respectively. In general, similar trends were observed during dynamic model digestion. However, both the degree of hydrolysis and the ACE inhibitory activity were influenced in the dynamic system by controlling pH and transit time between stomach and duodenum reactors to simulate conditions in the upper gastrointestinal tract. During the first 30 minutes of dynamic model digestion, significantly (p<0.05) higher ACE inhibitory activity was generated from unheated SPI after sequential digestion in both reactors compared to after peptic digestion - only in the stomach reactor. However, after 90 minutes, subsequent digestion by pancreatin of unheated SPI and blanched-sterilized SPI in the duodenum reactor resulted in significantly (p<0.05) lower ACE inhibitory activity compared to the corresponding peptic digests. At that time, IC50 values for unheated SPI, blanched-pasteurized SPI, and blanched-sterilized SPI were 0.38 + 0.01, 0.37 + 0.02, and 0.44 + 0.02 mg/mL, respectively. For both batch and dynamic digestion, heat processing of SPI by blanching and sterilizing decreased the ACE inhibitory activity of resulting soy digests. Chromatographic fractionation of unheated SPI digest resulted in IC50 values of active fractions ranging from 0.13 + 0.03 to 0.93 + 0.08 mg/mL. Although many of the fractions showed ACE inhibition, peptides with lower molecular weights and higher hydrophobicity were most active. This study suggests the potential generation of peptides with ACE inhibitory activity upon physiological digestion of soy protein, including products that have been subjected to heat processing.

Text

2009-12-10

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http://hdl.handle.net/2429/16336

Food Science

University of British Columbia

UBCV

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