Predisposing Factors Contributing to Spoilage of Soy Sauce by Aspergillus ochraceus
2008
Sumague, Ma. Josie V. | Mabesa, Reynaldo C. | Dizon, Erlinda I. | Carpio, Ernesto V. | Roxas, Ninfa P.
The study investigated the factors that predispose soy sauce to spoilage by Aspergillus ochraceus (e. g., dilution, inoculum, incubation temperature and incubation period). Determinants of spoilage monitored were viable count of A. ochraceus, pH, lactic acid content and sodium chloride content of soy sauce. Dilution, inoculum and incubation temperature significantly affected the viable count and pH of soy sauce inoculated with A. ochraceus at 95% level of confidence. Dilution, inoculum, temperature and incubation period significantly affected the lactic acid content and sodium chloride content of soy sauce inoculated with A. ochraceus at 95% confidence level. Among the factors studied, dilution and inoculum were the most important factors that affected all the determinants of soy sauce spoilage. These factors were most responsible for predisposing soy sauce to spoilage. Optimum spoilage conditions of soy sauce by A. ochraceus were found at a dilution range of 58-63% and inoculum of 14-17%. Under these conditions, soy sauce had a viable count of 7 (log10 CFU mL-1) A. ochraceus, pH of 5.7-5.8, 0.5-0.6% lactic acid and 7.0-8.0% sodium chloride. The multiplication of A. ochraceus in diluted soy sauce indicated that this microorganism is a slight to moderate halophile. Soy sauce in the original unaltered state is very stable. It has to be diluted to 53-63% to trigger its spoilage by A. ochraceus. Furthermore, it had to be inoculated with very high levels of inoculum than what may be normally encountered in nature for it to spoil. This indicates that the combined effect of sodium chloride and lactic acid concentration was effective in preserving soy sauce.
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