Inactivation of Salmonella on Fresh-cut Cantaloupes and Strawberries Using Citric Acid and Ultraviolet-C

Introduction: Fresh-cut fruits are frequently contaminated with various microorganisms during processing and have been implicated with several foodborne illness outbreaks including salmonellosis. Both ultraviolet-C (UV-C) and organic acids have been reported to reduce microbial loads on fresh produce.

Purpose: This study evaluated the effectiveness of citric acid, UV-C, and a combined citric acid and UV-C treatment for reducing Salmonella counts on fresh-cut cantaloupes and strawberries.

Methods: Fresh-cut cantaloupe cubes (pH 6.3) and strawberry halves (pH 3.4) were spot inoculated with 10 μl (10⁹ CFU/ml) of a bacterial cocktail containing four serotypes of Salmonella. After drying for 45 min, inoculated fruit samples were treated with 2% citric acid for 10 min, UV-C (1,200 Joules) for 5 min, or 2% citric acid for 10 min followed by UVC (1,200 Joules) for 5 min. To determine the effectiveness of these treatments, viable Salmonella counts were determined using Xylose Lysine Deoxycholate agar.

Results: The 2% citric acid treatment did not significantly reduce Salmonella counts on the two fruit samples. The UV-C treatment caused about 1.0 log reduction of Salmonella on both fruits. Treating cantaloupe samples with citric acid prior to UV-C did not enhance the effect of UV-C on Salmonella.  However, treating strawberry samples with citric acid first followed by UV-C treatment resulted in >3 log reduction of Salmonella.

Significance: The study suggests that the combined treatment of 2% citric acid and UV-C was effective in reducing Salmonella on the surface of strawberry and it could be potentially used to inactivate Salmonella on other similar fresh cut produce to improve food safety.