In miso, due to the substantial presence of genistein, flazin is often overlapped and masked by genistein in HPLC analysis. Flazin in the miso extracts could be resolved with genistein through medium-pressure liquid chromatography run under a nonacidified methanol-water system and subsequently fractionated by semipreparative HPLC and identified by NMR spectroscopic analysis. As referenced, flazin was detected in all 11 locally marketed miso products, with contents ranging from 3.5 to 124.8 μg/g. In lab-made miso fermented at 28 and 37 °C for 8 weeks, flazin formed faster at 37 °C than at 28 °C. Based on the time-dependent HPLC chromatographic changes of the miso extracts during fermentation, the presence of tryptophan-derived ß-carboline intermediates was deduced. Tryptophan was then supplemented for miso fermentation, and four peak substances were targeted for isolation by sophisticated approaches. Four ß-carbolines were purified and instrumentally identified, i.e., P1: 1-(1,3,4,5-tetrahydroxypentyl)-9H- pyrido[3,4-b]indole, P2 (diastereomer of P1): 1-(1*,3,4,5-tetrahydroxypentyl)- 9H-pyrido[3,4-b]indole, and Miso 101: 1-(1,3,4,5-tetrahydroxypentyl)-9H- pyrido[3,4-b]indole 3-carboxylic acid, and Miso 111 (diastereomer of Miso 101): 1-(1*,3,4,5-tetrahydroxypentyl)-9H-pyrido[3,4-b]indole 3-carboxylic acid. Each of the purified β-carbolines along with tryptophan and flazin exhibited varied ABTS·+ scavenging and xanthine oxidase inhibitory activities.
Keywords: flazin; miso; tryptophan; xanthine oxidase inhibition; β-carbolines.