Abstract
Microorganisms play an important role in the fermentation of soy sauce as they produce flavoring compounds which contribute to the desired taste and quality of soy sauce. The aim of this study was to isolate and identify halophilic microorganisms that are involved in the first stage (Koji) and second stage (Moromi) of soy sauce fermentation. In this study, soy sauce samples were collected from a local company located in Johor Bahru. The microorganisms were identified using Analytical Profile Identification (API) system and 16s ribosomal RNA (bacteria)/Internal Transcribed Spacer region (fungi and yeast) sequencing. In the koji fermentation, one fungus was isolated and identified as Aspergillus oryzae. During the moromi fermentation, one lactic acid bacteria and two yeasts were identified, including Tetragenococcus halophilus, Candida versatilis and Candida etchellsii. These halophilic microorganisms can be used as starter culture in moromi stage to shorten the fermentation period.
Highlights
Soy sauce is a traditional fermented food that has been widely used as a seasoning agent with a salty taste in Asian and European countries
Halophilic lactic acid bacteria and yeasts were grown on MRS media and MEA media, respectively, and counted within 30-300 colony forming unit (CFU)/mL
As the salt concentration increases to 10%, most of the mesophilic bacteria could not tolerate with such salinity, incapable to survive
Summary
Soy sauce is a traditional fermented food that has been widely used as a seasoning agent with a salty taste in Asian and European countries. Soy sauce is made through natural fermentation with combination of soybean, wheat flour and salt. These combinations will produce an aromatic flavor, make it suitable for seasoning and coloring agent in cooking due to its salty and umami taste. The process of making soy sauce involved two steps: Koji fermentation and Moromi fermentation. Koji fermentation process includes the combinations of soybean, wheat flour, and inoculation of spore (Aspergillus oryzae). During Koji fermentation, the mold produces proteolytic and amylolytic enzymes through enzymatic reaction which later hydrolyze the soybeans into simpler forms. The hydrolyzed substrate will be utilized by the natural microorganisms including yeasts and lactic acid bacteria, and this is reflected by the decrease in pH value during moromi fermentation. The breakdown products will be converted into volatile compounds that are responsible for the development of aroma and flavor of the soy sauce
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