Purpose: The objective of this study was to develop growth/no growth (G/NG) model to predict minimum concentrations of NaCl and NaNO2 to control S. aureus in low-sodium conditions.
Methods: A mixture of S. aureus strains NCCP10826, ATCC13565, ATCC14458, ATCC23235 and ATCC27664 was inoculated in nutrient broth formulated with NaCl (0, 0.25, 0.5, 0.75, 1.0, 1.25, 1.5, and 1.75%) and NaNO2 (0, 15, 30, 45, 60, 75, 90, 105, and 120 ppm). The plates were then incubated at 4, 7, 10, 12, and 15°C for up to 80 days under aerobic and anaerobic conditions. Growth responses [growth (1) or no growth (0)] were then determined every 24 h by turbidity. The growth response data were analyzed to select significant parameters (P< 0.05) by a stepwise selection method, which were used to calculate minimum concentrations of NaCl and NaNO2 to inhibit S. aureus growth. The performance of developed G/NG models were eventually validated with observed growth responses.
Results: Under anaerobic storage, S. aureus growth was not observed. However, S. aureus growth was observed only at 10 - 15°C in aerobic storage. For single application of NaNO2, S. aureus growth increased at higher NaNO2 concentration at 10 - 15°C. Minimum concentrations of NaCl in combination of NaNO2 decreased (P < 0.05) to inhibit S. aureus growth at 10 - 15°C, as NaNO2 concentration increased. A concordance percentage between observed and predicted growth responses was about 88%.
Significance: This result indicates that the developed models should be useful in calculating minimum concentrations of NaCl and NaNO2 combinations to inhibit S. aureus growth in processed meat products.