Modeling the growth/no-growth boundaries of Clostridium sporogenes JCM1416 in “requeijão cremoso” as a function of pH and concentration of sodium chloride and nisin

In this study, predictive models were developed to assess the growth response of Clostridium sporogenes JCM1416 in “requeijão cremoso” as affected by pH, sodium chloride and nisin. A complete factorial design was performed using different formulations “requeijão cremoso”: pH (5.2, 5.6 and 6.0), sodium chloride (0.5, 0.75, 1.0, 1.25 and 1.5%) and nisin (0.0, 5.0, 7.5, 10.0 and 12.5mg/kg) totalizing 75 conditions. Packs with 150g of requeijão cremoso were inoculated with 103 spores/g following storage at 10 °C for up to 60 days. The counts of C. sporogenes JCM1416 were performed on TPGY agar on day zero and at the end point of storage after a heat shock (80 °C for 12 min). The formulations that allowed an increase in the population of C. sporogenes JCM1416 of >1 log CFU/g were assigned the value of 1 (growth), and the formulations in which the increase was <l log CFU/g were assigned 0 (no growth). Overall, the growth of C. sporogenes JCM1416 was inhibited by the increase of pH, salt concentration and nisin. Probability of growth was drastically reduced from 36% to 0% in “requeijão cremoso” formulations with pH= 5.2 and pH= 6.0, respectively. Similar behavior was also observed when salt concentration was increased. For instance, the increase in NaCl concentration from 0.5% to 1.5% led to a reduction in the probability of growth of C. sporogenes JCM1416 from 60% to 0%. Increasing of nisin concentration (0 to 12.5mg/kg) was effective in inhibiting the growth of C. sporogenes JCM1416 on “requeijão cresmoso” only when the formation had pH 5.2 and salt concentration up to 1.0%. In formulations with pH 6.0, C. sporogenes JCM1416 growth was inhibited even in the absence of nisin, highlighting its critical role in the inhibition of this bacterium and for the development of robust “requeijão cremoso” formulations.