Dehydrated fruits have been the subject of manufacturer recalls due to contamination with Salmonella. Scientists at USDA ARS (Wyndmoor, Pennsylvania) have investigated the survival of Salmonella on apple slices of six apple cultivars after dehydration and also following treatment with antimicrobial solutions (0.5%, w/w) and dehydration.
Samples of six apple cultivars (Envy, Gala, Red Delicious, Fuji, Pink Lady, Granny Smith) were cored and sliced into 0.4-cm rings, halved, inoculated with a five-strain composite of desiccation-resistant Salmonella, and dehydrated at 60°C for 5 h. First results showed that Salmonella survival on apple cultivars was correlated to apple pH. Salmonella survival on Envy, Gala, Red Delicious, Fuji, Pink Lady, and Granny Smith was 5.92, 5.58, 4.83, 4.68, 4.45, and 3.84 log CFU, respectively. "There was significantly greater Salmonella inactivation on Granny Smith, Pink Lady, and Fuji apples than on Gala and Envy" the scientists say.
Subsequently, Gala apple slices were treated in 0.5% solutions of one of eight antimicrobial rinses for 2 min and then dehydrated. Survival of Salmonella on Gala apple slices following dehydration was 5.58 log CFU for the untreated control and 4.76, 3.90, 3.29, 3.13, 2.89, 2.83, 2.64, and 0.0 log CFU for those treated with potassium sorbate, sodium benzoate, ascorbic acid, propionic acid, lactic acid, citric acid, fumaric acid, and sodium bisulfate, respectively. Pre-treatment of apple slices with either fumaric acid or sodium bisulfate before dehydration led to lower significantly Salmonella survival.
Cultivar choice and antimicrobial treatments are fundamental to inactivate Salmonella in dried apples. "Lower apple pH was statistically correlated with decreasing survival of Salmonella following dehydration. Fumaric acid or sodium bisulfate inactivated Salmonella more than other treatments. This study may provide methodology applicable to the food industry for enhancing the inactivation of Salmonella during the dehydration of apple slices," the scientists conclude.
Source: Gurtler J., Keller S., Fan X., Olanya M., Jin T., Camp M., 'Survival of Salmonella during Apple Dehydration as Affected by Apple Cultivar and Antimicrobial Pre-treatment', 2020, Journal of Food Protection, Vol. 83 (5), pages 902–909.