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

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 degrees C). The observed data were fitted to the Gompertz and Baranyi models. Growth rate (mu(max)) and lag time (lambda) 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. mu(max) decreased, whereas lambda 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. (C) 2012 Elsevier Ltd. All rights reserved.