| Summary: | Biologically active peptides are found in the amino acid sequence of bacterial, fungal, plant and animal proteins. They are among the most potent pharmacologically active agents. Examples are venom toxin (mellitin), hormones (oxytoxin), opioids (beta-endorphin) and enzyme inhibitors (hirudin). These bioactive peptides are released from proteins by enzymatic proteolysis by processes such as gastrointestinal digestion or food processing. === Soybeans were fermented with Bacillus subtilis ATCC 41332 and Rhizopus oligosporus NRRL 2710 to produce tempeh and natto, respectively. Samples were taken throughout the fermentation and analysed for biochemical changes. Protease activity and ammonia production detected in the early stage of the tempeh preparation suggested that protein was used as a carbon source during that period and contributed to a rise in pH. Bacillus subtilis did not produce ammonia and maintained a constant pH throughout the fermentation. The total peptides produced were at a maximum at the end of the fermentation cycles. Angiotensin-converting enzyme inhibitory activity increased throughout both fermentations. A method was developed to monitor the production of biogenic amines throughout the fermentation. The levels of biogenic amines increased dramatically as the fermentation proceeded until maturity was achieved. In the tempeh fermentation, the polyamines levels rose from the initial 19 ppm to final concentration of 862 ppm, with the largest increase in histamine (616 ppm) followed by putrescine (204 ppm). These compounds also contributed to the pH rise from 3.8 to 6.8 in 24 h. In the Bacillus fermentation, the total polyamines at the end of the fermentation was 110 ppm with the largest increase in putrescine, followed by cadaverine. === Soy hydrolysate and the soy fermented foods, natto and tempeh, were deglycosylated and treated with proteolytic enzymes (plasma proteases, kidney homogenate, pronase, pepsin, thermolysin, trypsin, chymotrypsin and proteinase K) to produce oligopeptides. Several peptides were isolated, purified and characterized. The peptides had a range of biological activities---angiotensin converting enzyme inhibitory, antithrombotic, surface tension, antibacterial, anti-oxidant and insulin-modulating activities. Three potent ACE inhibitors, three thrombin inhibitors, five peptides with surface-active properties and one peptide with antibacterial activity were identified. They were all derived from glycinin and were found in the plasma protease digest, the kidney homogenate digest and the pronase digest of fermented foods. Another sequence ELLVYLL possessed good surface active properties but its precursor could not be identified. However, it was analogous to a peptide produced by Bacillus subtilis , and was probably synthesized during fermentation. Peptide analogs were synthesized and evaluated. They showed similar activities. Other sequences of known inhibitors, TPKDFEEIPEE, FPRGGG and DFEEIPEEL, were found to be competitive substrates for ACE.
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