Isolation and Identification of Aspergillus oryzae and the Production of Soy Sauce with New Aroma

Abstract

Soy sauce is a dark brown salty liquid with a peculiar and a meaty taste. It is the chief savory-seasoning agent used in Oriental cookery, but it is becoming increasingly popular in many other regions of the world. The purpose of this study was to isolate Aspergillus oryzae strain from contaminated rice, soybean and wheat for using in soy sauce production with new aroma of thyme and dill. Samples of rice, soybeans and wheat assumed to be contaminated with Aspergillus oryzae were used in the isolation. Pure cultures obtained by culturing and subculturing on Potato Dextrose Agar (PDA) were maintained on PDA slant. All isolates were inoculated on Aspergillus flavus and Parasiticus agar (AFPA) medium to differentiate them from Aspergillus flavus and Aspergillus parasiticus based on reverse color. These isolates and the reference strain were inoculated on Czapack Yeast Extract Agar (CYA) and the macroscopic characteristics amongst these strains were compared. Slide cultures for these strains were prepared and their microscopic characteristics were compared. The preparation of the soy sauce was carried out by two stages. The first stage was Koji, which was prepared by mixing the isolates and the reference strain separately with steamed soybeans and the crushed millet was incubated for three days. The second stage involved the preparation of brine which consists of a koji and salt solution. The obtained data were analyzed using SPSS program. The results of analysis of soy sauce encouraged the use of the isolates, especially the rice isolate in soy sauce production and the addition of dill or thyme gave a specific aroma to the final product.