EFFECTIVENESS OF UV-C IRRADIATION ON GROWTH OF POST-INOCULATED LISTERIA MONOCYTOGENES ON FRESH-CUT BROCCOLI

Abstract

Ultraviolet (UV) light irradiation has demonstrated positive effects as a postharvest treatment in prolonging the storage life of fresh produce and as a non-thermal method of inactivation of pathogenic microorganisms. The objective of this research was to study the effectiveness of UV-C light irradiation as a postharvest treatment on the subsequent attachment and growth of human pathogens on fresh produce. Fresh-cut broccoli is highly perishable and susceptible to deterioration and contamination by pathogenic microorganisms after harvest. Fresh-cut broccoli branchlets were treated with UV-C doses of 2.5 and 5 kJ/m2 and inoculated with Listeria monocytogenes at various times (0, 6 and 24 h) after treatment. Growth of the bacteria on UV-C treated surfaces of broccoli branchlets was evaluated by extracting and enumerating the microorganisms on day 3, 4, 6, and 8 after treatment. Results of the study show UV-C irradiation at a dose of 5 kJ/m2 was able to restrict the growth of L. monocytogenes in the samples inoculated 24 h post treatment, with no significant differences (P=0.05) in colour and weight loss of the broccoli compared to the control treatments. These results imply UV-C treatment may be effective not just in controlling pre-existing pathogens but also reducing the risk of post-harvest contamination. Previous studies have suggested that mild stress produced by UV-C light irradiation stimulates the synthesis of defence related phytochemicals in broccoli (such as glucosinolates) which also offer a variety of health benefits. It is not yet clear whether this mechanism is also responsible for the restriction of L. monocytogenes attachment and growth after UV-C irradiation.