UV-C Inactivation of Bacteria Artificially Inoculated on Apricot Fruit in Laboratory and Commercial Settings

Introduction: Washes with chemical sanitizers such as chlorine are commonly used by the fresh produce industry to sanitize wash water and fresh produce.  Some soft fruit, such as tree-ripened apricots, cannot be washed with aqueous sanitizers, due to their innate softness and delicate surfaces. Non-aqueous interventions are needed to enhance microbial safety of this type of fruit.

Purpose: The objective of this study was to investigate the efficacy of ultraviolet-C (UV-C) light in inactivating Escherichia coli O157:H7, Salmonella spp. and E. coli ATCC 25922 on apricots in the laboratory, and in inactivating an E. coli surrogate at a commercial setting.  

Methods: Robada apricots were dip-inoculated with cocktails of 5 strains of E. coli O157:H7, 4 strains of Salmonella spp., and E. coli ATCC 25922.  UV-C treatment was conducted at an intensity of ~13 mW/cm².  Fruit was rotated during the UV-C treatment. The efficacy of a UV-C treatment system (two treatment chambers connected by an inclined belt to rotate apricots between chambers) was also tested in a commercial setting.

Results: Results showed that in the laboratory setting using the rotating device, UV-C at a dose of ~125 mJ/cm² reduced populations of E. coli O157:H7, Salmonella spp. and E. coli ATCC 25922 by 1.5, 2.1, and 1.8 log CFU/fruit, respectively.  Further increases in UV-C doses achieved higher reductions of the bacteria.  In the commercial setting, the reductions of E. coli ATCC 25922 were only 0.5 - 0.7 log CFU/fruit even though similar or higher average doses of UV-C were used. Further evaluation using film dosimetry revealed that there were large variations in UV-C doses among varying apricot surface locations at the commercial trial.

Significance: This study demonstrates the need of using a better rotation device more capable of delivering uniform UV-C dosage to the surface of apricots for inactivating human pathogens in commercial settings.