Predisposing Factors Contributing to Spoilage of Soy Sauce by Bacillus circulans
Ma. Josie V. Sumague1*, Reynaldo C. Mabesa1, Erlinda I. Dizon1,
Ernesto V. Carpio1, and Ninfa P. Roxas2
1Food Science Cluster and 2Animal and Dairy Sciences Cluster,
College of Agriculture, University of the Philippines Los Baños, College, Laguna
This study investigated the factors that predispose soy sauce to spoilage by Bacillus circulans. Factors studied that would likely spoil soy sauce were dilution, inoculum, incubation temperature, and incubation period. Determinants of spoilage monitored were viable cell count of B. circulans, pH, titratable acidity, and sodium chloride content of soy sauce. Dilution, inoculum, and incubation temperature significantly affected the viable cell count and pH of soy sauce inoculated with B. circulans at 95% level of confidence. Dilution, inoculum, temperature, and incubation period significantly affected the titratable acidity, and sodium chloride content of soy sauce inoculated with B. circulans at 95% confidence level. Dilution and inoculum were the most important factors that affected all the determinants of soy sauce spoilage. Optimum conditions for spoilage of soy sauce by B. circulans were found in the range of 70-80% dilution and 14-18% inoculum. Under these conditions, soy sauce has viable cell count of 8 (log CFU/mL), pH of 5.7-6.5, 0.2-0.4% titratable acidity, and 4.0-6.0% sodium chloride content. The multiplication of B. circulans in diluted soy sauce indicated that this microorganism is slight to moderate halophile. Soy sauce in the original unaltered state was very stable.
Soy sauce is a light brown to black liquid with a meat- like, salty flavor produced from soybeans with or without wheat by means of two stages of fermentation (Steinkraus 1983). Sodium chloride (18%) is added to soy sauce as preservative to inhibit spoilage microorganisms. However, soy sauce can also be spoiled by salt loving microorganisms called halophiles.
Halophiles are microorganisms that require certain amount of sodium chloride for their growth. These microorganisms are classified according to the amount of salt necessary for their growth. Slight halophiles grow optimally in media containing 2-5% salt, moderate halophiles in media containing 5-20% salt, and extreme halophiles in media containing 20-30% salt (Baross & Lenovich 1992).
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