Reduction of histamine in fish sauces by rice bran nuka

Fish sauce products often contain a quantity (>1000 mg/L) of histamine (Hm). We investigated the Hm-reducing activity of 39 traditional fermented food products, including fish- and radish-nukazuke (fermented food with rice bran (nuka)), radish- and turnip-kojizuke (fermented food with malted rice (koji)), miso (fermented soy paste), natto and yogurt, in fish sauce products. The nuka-paste portion of radish-nukazuke showed the highest Hm-reducing activity. The addition of the nuka-paste (20%, w/v) to sardine fish sauce (iwashi-ishiru) reduced the Hm content to about 600–700 mg/L from 1200 mg/L. The Hm-reducing activity of nuka-paste was regarded as water-soluble, heat tolerant, and of high molecular weight. Although raw-nuka showed the Hm-reducing activity, the fermentation process slightly increased the activity of the raw-nuka and their extract solution. These results indicated that nuka, a byproduct of rice polishing, could be utilized for Hm reduction of fermented fish products.