Liberation of eicosapentaenoic acid and degradation of the major cell wall polysaccharide porphyran by fermentation of nori, the dried thalli of Pyropia yezoensis, with koji

Abstract

In this study, dried sheets of nori, shredded and processed thalli of the red alga Pyropia yezoensis, were fermented with either barley, rice or soybean koji. High-performance liquid chromatographic analyses of the lipid extracts of the fermented products indicated that the fermentation of nori with all kinds of tested koji released free fatty acids, including the eicosapentaenoic acid, from ester lipids. We found that approximately half of the eicosapentaenoic acid in nori had been released as the free fatty acid at up to 4 weeks of fermentation at 30 °C and more than 65% at 8 to12 weeks in the fermented products with barley and rice koji. We also demonstrated the degradation of porphyran, a major cell wall polysaccharide of nori, by gel chromatography on Sephacryl S-300 HR of hot water extracts of the fermented products of nori with barley koji. Approximately two-third of porphyran had been degraded to porphyran oligosaccharides up to 6 weeks of fermentation. Fermentation of nori with koji may bring out the potential health-promoting functions of nori.