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UV-C radiation has been used in different areas of food industry due to its germicidal properties. Besides that, in the case of products with metabolic activity such as fresh fruits and vegetables these treatments can result in other beneficial modifications such as reducing the ripening rate and delaying senescence. Most studies performed to date have focused on selecting an appropriate UV-C dose for each commodity, but very little attention has been focused on determining the influence of radiation intensity or fluency (radiant energy per unit area an per unit time) for a given dose. In this study, we evaluated the effect of radiation intensity on the efficacy of UV-C treatments of fresh fruits. We analyzed two fruits that have been usually used as model systems: strawberry, a non climacteric fruit with very high ripening rate and that accumulates anthocyanins as major pigments, and tomato, a climacteric commodity with moderate metabolic activity, in which colour is determined by carotenoids. Strawberries cv. Camarosa were harvested with 75% of surface colour red, and tomatoes cv. Elpida were harvested at the breaker ripening stage. Both types of fruits were treated with a dose of 4 kJ m of UV-C radiation, under two different intensities (3 or 33 W m). After that, fruits were put in plastic trays and covered with perforated PVC in order to avoid CO2 accumulation and were stored at 10 or 20 oC in the case of strawberry or tomato, respectively. For each type of fruit a group was left untreated, packed and stored as previously described and used as a control. Immediately after the treatments and during storage we determined decay, weight loss, surface colour (lightness, hue angle and chroma), anthocyanin content or lycopene in strawberry and tomato, respectively, firmness, acidity, soluble solids, antioxidant capacity and respiration rate. We also evaluated the number of CFU (Colony Forming Units) for mesophylic bacteria and molds and performed a consumer preference test. UV-C treatments, independently of the intensity of radiation used, were useful to reduce dehydration, decay and deterioration in both fruits, but the effects were more marked in strawberry. The increase in radiation intensity resulted in better control of postharvest rots in both tomato and strawberry. The treatments with an intensity of 33 W m reduced weight loss at the end of the storage period. In strawberry after 5 d at 10 oC, decay was 68% in the controls, 53% in the fruit treated with the lowest intensity of UVC radiation and only 12% in the fruit treated with the highest fluency. In tomato, the percentage of decayed fruit at the end of the storage period was 23, 8 and 6% in control or fruit treated with 3 o 33 W m of UV-C radiation, respectively. Exposure to UV-C also clearly delayed strawberry fruit ripening as detected by lower softening and anthocyanin accumulation and less red colour development. The effects were more drastic with the highest UV-C intensity. In tomato, the influence of the UV-C treatments on ripening was lower than in strawberry and was similar for both radiation intensities evaluated. Neither the strawberries nor the tomatoes showed at any of the radiation intensities significant differences with the controls in acidity, soluble solids or antioxidants. Respiration rate of tomato fruit increased during storage and no differences between control and treated fruit were observed. In strawberry after 5 d at 10 °C, control fruit showed higher respiration rate than UV-C treated fruit at both radiation intensities assayed. Sensory analysis in both tomato and strawberry performed by an untrained panel indicated a clear preference for treated fruits and between them to those exposed to the highest intensity. Finally, counts for bacteria and mold showed moderate reductions immediately after the UV-C treatments. In strawberry, at the end of the storage period the differences were clearer showing fruit treated with the highest intensity lower CFUs than control and low intensity-treated fruit.

Efecto de la intensidad de la radiación UV-C sobre la calidad sensorial, microbiológica y nutricional de frutos