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UV light and ultrasound to inactivate bacteria in fresh-cut produce

Scientists of Environmental Microbiology Unit at Patras University (Greece) and of Quality Control Department of Ministry of Rural Development and Food at Patras have investigated the effect of two disinfection non-thermal treatments, UV light and Ultrasound (US), on bacterial decontamination and color in fresh-cut lettuce and strawberry. Mainly, the scientists have evaluated the efficacy of UV and US on the sanitation of inoculated lettuce and strawberry with a mix of Escherichia coli, Listeria innocua, Salmonella Enteritidis and Staphylococcus aureus.

The UV treatment was performed at an intensity of 2 mW/cm2 testing 5 dosages: 1.2, 2.4, 3.6, 5.4, and 7.2 J/cm2 for 10, 20, 30, 45, and 60 minutes. Sample temperature was monitored to ensure that it was at 25°C also at the end of the longest exposure time. The US treatment was performed at a frequency of 37 kHz for 10, 20, 30, 45, and 60 minutes.

Results showed that UV treatment on fresh-cut lettuce 
significantly reduced the populations of E. coli, L. innocua, S. Enteritidis, and S. aureus by 1.75, 1.27, 1.39 e 1.21 log CFU/g, respectively. In addition, the populations of E. coli and S. Enteritidis were reduced by over 2 log CFU/g using US treatment. Significant reduction of all bacteria was reached after 20 min by UV light and after 30 min by US treatment.

In strawberries, the UV treatment was less effective than US because UV reduced bacteria only by 1-1.4 log CFU/g, while US reduced the population of E. coli, S. aureus, S. Enteritidis, and L. innocua by 3.04, 2.41, 5.52, and 6.12 log CFU/g, respectively. Significant reduction of all bacteria was reached between 10 and 30 min by UV light and between 30 and 45 min by US.

As regards the overall appearance, firmness, and color, UV light and US treatment applied for a maximum exposure time of 45 min do not 
negatively affect the product quality.

Being UV light and ultrasound non-thermal, safe, non-toxic, and environmental friendly technologies, the results suggest their application in fresh-cut industry as potential and effective alternatives to the traditional chemical sanitizers, such as chlorine and hydrogen peroxide, which are widely used in the minimal processing.

Source: Birmpa A., Sfika V., Vantarakis A., "Ultraviolet light and Ultrasound as non-thermal treatments for the inactivation of microorganisms in fresh ready-to-eat foods", International Journal of Food Microbiology, 2013, FOOD-06226. Further info:

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