Perlolyrine Formation and Isoflavones Hydrolysis During Miso Fermentation Affected by Tryptophan and Tryptamine

Perlolyrine and flazin are bioactive β-carbolines belonging to naturally occurring alkaloids. In this study, perlolyrine was first isolated and identified in miso fermented at 50°C for 8 weeks. As affected by tryptophan and tryptamine-supplemented for fermentation and based on standard curves constructed by the isolated perlolyrine and flazin, perlolyrine ca. 0.83 mg/g miso was formed in both, whereas flazin ca. 3.9 mg/g miso was produced in the tryptophan-supplemented miso. As assessed and noticed spontaneously, hydrolysis of the miso isoflavones was potently inhibited by supplemented tryptamine. This inhibitory effect was also observed in hydrolysis of a soy-isoflavone isolate as a substrate by rice koji extract or almond β-glucosidase. In a model investigation, para-nitrophenyl-β-d-glucopyranoside (pNPG) was extensively hydrolyzed by β-glucosidase (in phosphate-buffered saline [PBS], pH 7.4) in the presence of tryptophan, but the reaction was inhibited by tryptamine in a dose-dependent manner. In quantification of para-nitrophenol (pNP) released from hydrolysis of pNPG at various concentrations, it shows that the electrostatic status attributed to different isoelectric points of tryptamine and tryptophan may exhibit mixed-competitive hindrance or blockage of the β-glucosidase-like activity originating from rice koji and result in varied effects on miso isoflavones hydrolysis. PRACTICAL APPLICATIONS: This study marks the first successful isolation and identification of perlolyrine and flazin-both are naturally occurring bioactive alkaloids-in miso. Miso fermentation is not only a traditional process in production of the historical fermented food but also identified as a carrier-food enriched with β-carbolines. Spectacularly, formation of these compounds could be enhanced by supplementation of tryptophan for miso fermentation.