Effect of Ripening Stage and Storage Temperature on the Survival and Internalization of Salmonella Typhimurium in ‘Maradol’ Papaya Fruit

Recent foodborne outbreaks by Salmonella Typhimurium associated with the consumption of ‘Maradol’ papaya have prompted an assessment of the pathogen’s behavior with regard to the fruit. The objective of this research was to assess the survival and possible internalization of S. Typhimurium in inoculated ‘Maradol’ papaya harvested at two maturity stages and stored for various days at 11 °C and 24 °C. The physicochemical analysis on fruit included firmness (N), total soluble solids (%), and pH. The location of S. Typhimurium in fruit exocarp and mesocarp tissues was observed using confocal laser scanning microscopy (CLSM). Results indicated that the high temperature (24 °C) was the most important factor for the survival of S. Typhimurium. At this same temperature, it was the variable firmness that was the most affected, regardless of storage days, whether inoculated or not. The principal component analysis (PCA) separated the data into two components that explained 57% of the variance. PC1 linked higher S. Typhimurium populations with declining firmness, TSS, and exocarp pH were found in fruit stored at 24 °C, whereas PC2 was associated with moderate physicochemical changes at 11 °C. The CLSM observations confirmed superficial colonization of the bacteria on papaya fruit rather than an internalization but only at 24 °C, regardless of ripening stage throughout the 7 days sampling period. Maintaining the cold chain is essential to mitigate the risk of salmonellosis in papaya.