FORMATION BY YEAST OF AROMA COMPONENTS SPECIFIC TO MISO AND EFFECT OF AROMA COMPONENTS ON THE CHANGES OF AROMA IN MISO SOUP BY HEATING

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4-Hydroxy-2 (or 5)-ethyl-5 (or 2)-methyl-3(2H)-furanone (HEHF) which was first identified by the author as an aroma component of red salty rice miso (fermented soybean paste), has a strong, sweet cake-like aroma with a threshold value of less than 0.04 ppb. It is a unique compound and is abundant in red salty rice miso and shoyu (soysauce). The formation of HEMF by yeast was examined in an attempt to investigate its mechanism and involved factors. HEMF formation was promoted by yeast cultivation in a heat-sterllized medium which included glucose, ribose, and a nitrogenous compound such as an amino acid. It is suggested that HEMF was formed during the cultivation of yeast by using a precursor of HEMF which may have been produced by the amino-corbonyl reaction of pentose with amino acids during heating.Halophilic yeast Z.rouxil, grown in a heat sterilized medium containing ribose and glycine in buffer solution of KH_2PO_4 and MgSO_4・7H_2O, forms appreciable amount of aroma compound HEMF in the medium. The precursor of HEMF was considered to be formed stably in buffer solution of KH_2PO_4 and MgSO_4・7H_2O. The concentration of ribose in medium was considered to appropriate from 20 mmol to 300 mmol. These results were indicated probably that HEMF was formed from amino-carbonyl reaction product heated ribose and glycine, and acetaldehyde or similar reactive substance to acetaldehyde formed by yeast.The changes of aroma in miso soup by heating were evaluated with the odor-descriptive terms of food products developed by Shimoda et al.. The mechanisms of the changes of aroma in miso soup by heating were investigated by the method of Gas Chromatography-Olfactometry. By comparison of the flavor dilution (FD) factor of each aroma component in raw and heated miso, the changes were considered that HEMF decomposed and methional was formed newly by heating.