Effect of pH and storage conditions on Listeria monocytogenes growth inoculated into sapote mamey (Pouteria sapota (Jacq) H.E. Moore & Stearn) pulp

Abstract

Sapote mamey is a highly perishable tropical fruit when stored fresh, with a shelf life of 8–10 days at room temperature. Its agreeable taste and nutritional content are valuable characteristics which can be preserved as a pulp, normally at low temperatures, to maintain initial quality. However, this type of fresh product can potentially be a substrate for pathogenic microorganisms like Listeria monocytogenes, which can survive at refrigeration temperatures. The objectives of this investigation were to determine growth, survival conditions and then establish hurdles, of L. monocytogenes inoculated into mamey pulp under different levels of ascorbic acid (0, 250, and 500 mg/kg), pH (4.0, 4.5, and >5.0), and temperature (4 and 10 °C). The observed data were fitted to the Gompertz and Baranyi models. Growth rate (μmax) and lag time (λ) of L. monocytogenes were estimated using the modified Gompertz model given that it presented a better goodness of fit and accuracy in the modeling. Growth was favored at pH >5.0. μmax decreased, whereas λ increased, as the levels of ascorbic acid and temperature increased. A pH of 4.5 hinders but does not inhibit bacterial growth, while a pH of 4.0 inhibited growth of L. monocytogenes for 15 days at both storage temperatures.