Growth of Salmonella spp. in the Peel and in the Pulp of Avocado (Persea americana)

Introduction: The occurrence of cases and outbreaks of foodborne illness associated with the consumption of fruit have been reported in the last years. Data from epidemiological investigations indicate that Salmonella is the main etiological agent associated with foodborne disease outbreaks involving fruits. Avocado is a tropical fruit produced in Brazil, whose consumption and exports have increased in recent years. Despite this, no data on the behavior and on the growth kinetics parameters of Salmonella in this fruit are found in the literature. This fact is of great concern, since it is known that the low acid fruits constitute optimal substrates for the multiplication of microorganisms, especially pathogens.

Purpose: To determine the growth kinetic parameters (maximum growth rate, µ; lag time; λ and maximum population, κ) of Salmonella spp. on the peel and in the pulp of avocado at 10, 15, 20 and 30°C. 

Methods: Samples of peel and pulp of avocado were inoculated with a cocktail of three strains of Salmonella spp. (Salmonella Typhimurium, Salmonella Enteritidis and Salmonella Montevideo) (10² to 10³ CFU/g) and further stored at 10, 15, 20 and 30°C. Sampling was carried out at different intervals and count was done using MLCB agar incubated at 37°C/ 24 h. The growth kinetic parameters were obtained by fitting the experimental data to Baranyi model using the DMFit software. The growth kinetic parameters of S. enterica were checked for significant statistical differences (P≤0.05) employing one-factor analysis of variances (ANOVA) followed by Skott-Knott test.

Results: The growth kinetic parameters indicated that Salmonella was able to grow on the peel and pulp of avocado from 10 to 30°C, presenting significant different λ and κ at 30°C (P<0.05). µ does not seem be influenced by substrate of growth (pulp or peel).

Significance: The results showed that avocado comprise substrates that allow the growth of pathogens such as Salmonella, both in the pulp and also in the peel, offering risk to public health.