FORMATION OF THE CHARACTERISTIC AROMA COMPONENTS OF MISO BY YEASTS AND THERMAL DEGRADATION OF THESE COMPONENTS

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HEMF(4-hydroxy-2(or 5)-ethyl-5(or 2)-methy1-3(2H)-furanone) was confirmed to contribute remarkably to sensory evaluation of rice-miso aroma from the results of chemical and statistical analyzes.The relationship between the formation of HEMF and the growth of yeasts in miso was investigated, comparing miso to which precultured-yeasts(Zygosaccharomyces rouxii) were added with miso to which they were not added. In yeast-added miso, HEMF was not detected by the 7th day after the preparation although the number of yeast cells was 1.6X10^5 cell/g. In miso without yeast, 0.06 ppm HEMF was detected when the number of yeast cells was 2.2X10^3 cell/g. The pH levels when HEMP was detected in these misos were 5.57 and 5.59 respectively. These results suggest that in miso containing a high concentration of reducing sugar and NaCl, HEMF was produced when the pH level fell to less than 5.6.HEMF was reported to be unstable when it was purified. Methionol was reported to contribute to the unpleasent odor produced by heating of miso. The meckanisms of the change of aroma in miso by heating were investigated with regard to HEMF and Methionol. The concentration of HEMF in the heated miso suspension decreased in the initial time of heating. The concentration of HEMF in the HEMF-added model solution decreased in the initial time of heating, to. 2-Propanone and 2,3-hexandione were confirmed to be produced from the HEMF-added model solution by heating. The concentration of Methionol in the heated miso suspension did not changed. Methional was identified in the heated miso suspension. Methional was not able to be detected in the Methionol-added model solution which was heated. Methional which was identified in the heated miso suspension was confirmed to be not product from Methonol in miso suspension.