Characterization of microorganisms involved in the second stage of soy sauce fermentation (moromi) and studies on the shelf life of soy sauce.

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Microorganisms play an important role in the fermentation of soy sauce. The aim of this study was to identify and characterize the microorganisms that are involved in the second stage of soy sauce fermentation and the shelf life studied. The microorganisms were identified using biochemical and Analytical Profile Identification (API) system. The pattern of distribution of total microbial numbers, lactic acid bacteria, yeast and fungi were similar as their numbers generally decreased with time. During the fermentation, lactic acid bacteria (numbers) were the most dominant followed by yeasts (numbers) and fungi (numbers). Twenty strains of lactic acid bacteria were isolated from the soy sauce mash during moromi fermentation and these were observed mostly in the first three weeks of fermentation. Tetragenococcus halophilus (also known as Pediococcus halophilus) had the highest number, followed by Lactococcus lactis, Lactobacillus delbrueckii, Lactobacillus plantarum and Lactobacillus acidophilus respectively. Two of the lactics could not be identified. Twenty-five strains of yeasts and molds were also isolated during moromi fermentation. The predominant yeast strain was Zygosaccharomyces rouxii (Z. rouxii), which was followed by Trichosporon mucoides, Cryptococcus humicolus, Cryptococcus laurentii, Candida ciferrii, Pichia ohmeri and Candida famata respectively. No significant changes were observed in microbial load, colour, moisture content, pH, and all the sensory attributes (colour, saltiness, pungency, umami and overall acceptability) of the locally produced soy sauce over the six months storage under room temperature. These results indicate that soy sauce can locally be produced by using starter culture to shorten the moromi stage fermentation and can stay on the shelf for more than six months.
A thesis submitted to the Department of Biochemistry and Biotechnology, Kwame Nkrumah University of Science and Technology, Kumasi, in partial fulfilment of the requirements for the award of Msc. Food Science and Technology.