Optimization of Formula of NaCl, pH and aw in Low-salt Soy Sauce against Zygosaccharomyces rouxii using Experimental Mixture Design

Introduction:  Processed foods with low contents of salt have been highly required due to current trend of healthy diet. Non-acid sauces that contain reduced salt have difficulties to meet requirements not only for better qualities but also stable shelf life at room temperature at the same time. However, it could be possible to solve those defects effectively by optimization of microbial growth factor formula like pH, a_w, salt contents simultaneously with applying statistical experimental method.

Purpose:  Purpose of this study was development of statistical regression model against Zygosaccharomyces rouxii in low-salt soy sauce by optimization of 3 kinds of key microbial growth factor such as NaCl, pH, a_wusing experimental mixture design to achieve stable shelf life at room temperature.

Methods:  Target product was low-salt soy sauce distributed at room temperature and target strain was Zygosaccharomyces rouxii KCCM11300 which is the most resistant to NaCl, a_w and pH out of tested strains. Strain was cultured in broth of low-salt soy sauce adjusted with NaCl (for NaCl 3.2~5.2%), acetic acid (for pH 4.0~5.0) and glycerol (for a_w 0.88~0.93) for 4, 7, 10, 14 days and enumerated their loads in each day. The experimental design was applied using Design Expert^® 8.0 software.

Results:  Model equation was obtained to optimize inhibitory interaction against Zygosaccharomyces rouxii KCCM11300 by adjusting NaCl, pH and a_w. According to this model, Zygosaccharomyces rouxii KCCM11300 could be inhibited in the condition of NaCl 5.0 % with pH 4.27, a_w 0.900 and with pH 4.30 and a_w 0.891, respectively, that it had been recorded same inhibitory pattern only using 15% of NaCl. Under these conditions, experimental data was closely identified with predicted model. Applied model was cubic mixture model with 0.94 of R².

Significance:  By using proposed equation, it could be highly expected that microbial spoilage in non-acid and low-salt sauces can be protected effectively to provide long shelf life at room temperature. This approach to reduce spoilage in low-salt sauces might be applied to develop other liquid types of foods as well as soy sauces.