Abstract
Thymol (THY), a generally recognized as safe (GRAS) compound found in thyme oil, has inhibitory effects against foodborne pathogens including Salmonella. Hydrogen peroxide (H2O2) is another GRAS agent to effectively inactivate Salmonella. The aim of the current study was to develop a GRAS wash solution containing THY (or H2O2) and other GRAS antimicrobials (organic acids and food surfactants) that would effectively reduce Salmonella enterica on grape tomatoes and minimize cross-contamination in washing water. A systematic approach including minimum inhibitory concentration and minimum bactericidal concentration tests, inhibition zone tests, and small-scale and scaled-up tomato washing tests was used to develop such wash solutions. Grape tomatoes surface-inoculated with S. enterica Typhimurium were washed with selected solutions containing combination of 0.2 mg/ml THY, 5 % sodium dodecyl sulfate (SDS) and 2 mg/ml acetic acid (AA), 800 ppm H2O2, combination of 200 ppm H2O2 with 4 % SDS, or 200 ppm chlorine for 2 min. THY 0.2 mg/ml + SDS 5 % + AA 2 mg/ml, 800 ppm H2O2, or 200 ppm chlorine achieved around 7.5 log reductions of Salmonella on the tomatoes as compared to the control in tests involving 10 or 100 g tomatoes. More than 5.0 log reductions in the spent washing solutions (0.2 mg/ml THY + SDS 5 % + 2 mg/ml AA; 800 ppm H2O2) was observed. None of these antimicrobial washes changed the color, pH, texture, sensory quality of the tomatoes during 16-day storage at 4 and 22 °C. These treatments also achieved a 1.3 log reduction of total aerobic bacteria. Thus, washing with 0.2 mg/ml THY + SDS 5 % + 2 mg/ml AA and 800 ppm H2O2 as alternative to chlorine-based washing could be an effective method to inactivate Salmonella on tomatoes and reduce the transmission of pathogens from tomatoes to washing solutions.
Published Version
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