Incidence and growth of Salmonella enterica on the peel and pulp of avocado (Persea americana) and custard apple (Annona squamosa)

The aim of this study was to assess the incidence and to estimate the growth kinetic parameters (maximum growth rate, mu; lag time, lambda; and maximum population, kappa) of Salmonella on the peel and pulp of avocado (Persea americana var. americana) and custard apple (Annona squamosa L.) as affected by temperature (10-30 degrees C). The incidence of Salmonella was assessed on the peel and pulp of the fruits (n = 200 of each fruit), separately, totalizing 800 analyses. Only three samples of custard apple pulp were positive for Salmonella enterica and the three isolates recovered belonged to serotype S. Typhimurium. Salmonella was not recovered from avocado and custard apple peels and from avocado pulp. Generally, the substrate (pulp or peel) of growth did not affect mu values of S. enterica (p > 0.05). Very similar mu values were found for S. enterica inoculated in custard apple and avocado. S. enterica presented the highest lambda in the peel of the fruits. The growth of S. enterica resulted in larger lambda in custard apple in comparison to avocado. For example, the lambda of S. enterica in the pulp of custard apple and avocado were 47.0 +/- 0.78 h and 10.0 +/- 3.78 h, respectively. The lowest values of kappa were obtained at the lower storage temperature conditions (10 degrees C). For instance, kappa values of 3.7 +/- 0.06 log CFU/g and 2.9 +/- 0.03 log CFU/g were obtained from the growth of S. enterica in avocado and custard apple pulps at 10 degrees C (p < 0.05), respectively. On the other hand, at 30 degrees C, kappa values were 6.5 +/- 0.25 log CFU/g and 6.5 +/- 0.05 log CFU/g, respectively. Significantly higher kappa were obtained from the growth of S. enterica in the pulp than in the peel of the fruits (p < 0.05). For instance, the growth of S. enterica in the pulp of avocada led to a kappa value of 6.5 +/- 0.25 log CFU/g, while in the peel led to a kappa value of 4.6 +/- 023 log CFU/g (p < 0.05). In general, growth kinetic parameters indicated that avocado comprises a better substrate than custard apple for the growth of S. enterica. The square root model fitted to the data obtained in this study and to the growth data available in the literature for other tropical low acid fruits indicated high variability in mu and lambda of Salmonella. The results obtained in this study show that whole low acid tropical fruits can harbor Salmonella, and that this foodborne pathogen can not only survive but also grow both on the peel and pulp of low acid tropical fruits, such as avocado and custard apple. (C) 2016 Elsevier B.V. All rights reserved.