Using a combined starter of Aspergillus oryzae and Saccharomyces cerevisiae microorganisms to produce soy sauce by natural fermentation

The development of soy sauce is actual by the growing interest in soy products, which can replace animal protein. Aspergillus oryzae are traditionally used to produce sauce by fermentation method. Recent research has approved that using combinations of microorganisms can reduce fermentation time and improve the nutritional value of the product. The aim of this study is to develop a soy sauce recipe using a combined starter of Aspergillus oryzae and Saccharomyces cerevisiae. The objects of the study are: soy sauce samples prepared using the different quantities of combined starter. During the fermentation there were carried out the following measurements: visual observations of the quantity of soluble solids by refractometry method and the ethanol content by a hydrometer. The optimal amount of starter was determined by studying the physicochemical parameters (pH, soluble solids content, titratable acidity, and antioxidant activity) and organoleptic properties (appearance, consistency, taste, aroma, and overall taste and aroma assessment) of the obtained samples. Based on scientific literature, it was suggested that the addition of Saccharomyces cerevisiae to start the fermentation process would possibly reduce the period of fermentation. Observations during fermentation confirmed the hypothesis. In this investigation the period of fermentation lasted 30 days. The pH, titratable acidity, and solids content of the sauce is related with GOST R 58434 "Soy Sauces." The obtained samples have high antioxidant activity of 10.46 mmol/L, which we explain by the use of Saccharomyces cerevisiae. The sample containing 3% of the total amount (15 grams) of starter has received the best organoleptic rating. The results highlighted the potential of the combined use of Aspergillus oryzae and Saccharomyces cerevisiae for making soy sauce.