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 ( p NPG) 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 ( p NP) released from hydrolysis of p NPG 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.