Isolation of Aspergillus oryzae and New Aroma Production for Soy Sauce

Abstract

Aspergillus oryzae is member of flavi group, used in fermentation of oriental foods for centuries. The purpose of this study is to isolate and characterize Aspergillus oryzae strain for using in soy sauce production with specific aroma, depending on local plants as thyme and dill. The isolates were cultured on Potato Dextrose Agar (PDA), Aspergillus flavus and parasiticus Agar (AFPA) was used to differentiate the isolates from Aspergillus flavus and Aspergillus parasiticus depended on the reverse color. C Zapeck Yeast Extract Agar (CYA) was used in identification. The preparation of the soy sauce was carried out by two stages. The first was Koji, which was prepared by mixing isolates and reference strains with steamed soybeans and crushed millet for three days. The second was the brine, which consisted of koji and salt solution. This stage was maintained for three months at 30°C by continuing stirring. The brine, then, was filtered, pasteurized and aroma plants were added. The enzymes of A. oryzae had the essential role in the fermentation process in addition to the lactic acid bacteria, Z. rouxii and C. versitils. The results of analysis of soy sauce showed that the pH was 4.16, 4.65, 4.25, the concentration of ethanol was 0.11%, 0.57%,0.92% (v/v), NaCl concentration was 14.04%, 16.38%, 15.4% (w/v) and Ca concentration was 123, 127, 102 (mg/100g) for the reference, rice isolate and soybean isolate, respectively. In addition, ash contents, total solids and moisture of our product were closed to the commercial one. The color of the soy sauce was dark brown with thyme and dill aroma. It can be concluded that the quantity of water was very critical in the fungus growth. Through the brine fermentation, proteins and carbohydrates were decomposed into their fragments a process accompanied by production of many flavors. The addition of dill and thyme were gave a specific aroma to the final product. The high salt concentration was very necessary to prevent any decay in the product.