The importance of the furanones HDMF and HEMF in the flavour profile of Japanese barley miso and their production during fermentation

All 13 samples of Japanese barley miso accepted for the Kumamoto Prefecture Miso Competition of 1995 were assessed by tasting and by GC analysis using FID, SIM and olfactometric detection. Forty three compounds were separated by GC, of which 15 had a detectable aroma. Consideration of the chemical and sensory analyses of this latter group showed that only the two furanones, 4-hydroxy-2,5-dimethyl-3(2H)-furanone (HDMF) and 4-hydroxy-2(or 5)-ethyl-5(or 2)-methyl-3(2H)-furanone (HEMF), correlated significantly with the quality of miso flavour (P < 0.05). Experimental fermentations of salted barley koji and full barley miso mash with Zygosaccharomyces rouxii resulted in alcoholic fermentation in all cases investigated. In contrast, production of the three furanones, HMMF (4-hydroxy-5-monomethyl-3(2H)-furanone), HDMF and HEMF, was very sensitive to the conditions used. Negligible amounts were found in the absence of soy beans and the highest levels occurred when the full mash was incubated at 37°C for 14 days before inoculation of the yeast. When pre-incubation was carried out, the concentration of HMMF was maximal at the end of mashing and declined during fermentation whilst the amount of both HEMF and HDMF increased. The time courses were consistent with synthesis of HEMF, and then HDMF, by the yeast from HMMF.