Submitted to: Postharvest Biology and Technology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/8/2014
Publication Date: 6/2/2014
Publication URL: http://handle.nal.usda.gov/10113/58856
Citation: Yan, R., Mattheis, J.P., Gurtler, J., Sites, J.E., Fan, X. 2014. UV-C inactivation of Escherichia coli and dose uniformity on apricot fruit in a commercial setting. Postharvest Biology and Technology. doi.org/10.1016/j.postharvbio.2014.04.005. Interpretive Summary: Tree-ripe peaches and apricots cannot tolerate washes due to their advanced ripeness and softness. A non-aqueous intervention technology is needed to enhance the microbial safety of this type of fruits. The efficacy of a UV-C treatment system in inactivating a surrogate of E. coli O157:H7 and maintaining apricot fruit quality was tested in a commercial setting. Results showed that apricot fruits were tolerant to high doses of UV-C without significant changes in fruit quality and efforts are needed to ensure fruit receiving uniform UV-C exposure for inactivating bacteria. The information is valuable for the fruit industry to modify the UV-C system for the production of safer and high quality fruit.
Technical Abstract: The efficacy of a UV-C treatment system (two treatment chambers connected by an inclined belt to rotate apricots between chambers) was tested in a commercial setting. Escherichia coli ATCC 25922, used as a surrogate for E. coli O157:H7 to determine the system’s antimicrobial efficacy, was inoculated onto fruit surfaces at a population of 6.8 log CFU/fruit. Fruit quality was evaluated (1) over 10 days storage at 20 C and (2) for 3 weeks at 2 C plus 3 days storage at 20 C. UV-C dosage was evaluated by attaching film dosimeters to six fixed locations on each apricot. Results suggested that firmness, soluble solids content, and titratable acidity of the fruit were not affected by two doses of UV-C (viz., 127 and 254 mJ/cm2 average doses). Even though instrumental color measurement indicated that L* values of the shaded side of the fruit were lower than those of non-treated fruits, no visible changes to surface color were observed. Reduction of inoculated E. coli ATCC 25922 populations (i.e., 0.5-0.7 logs) on the apricot fruit by UV-C treatment was not statistically significant. There were large variations in UV-C doses among varying apricot surface locations. Approximately 1/3 of apricots had individual surfaces receiving less than 20 mJ/cm2 UV-C exposure, even though fruits received, on average, more than 100 mJ/cm2. Low reductions of E. coli may be attributed, in part, to non-uniform UV-C exposure. Our results suggest that apricot fruits were tolerant to high doses of UV-C without significant changes in fruit quality. This study also demonstrates the need of using a fruit rotation device more capable of delivering uniform UV-C dosage to the surface of apricots for inactivating bacteria in a commercial setting.