Nutritional and nutraceutical quality of Vaccinium myrtillus and Vaccinium corymbosum fruits treated with UV-B radiation

Blueberries and bilberries, thanks to their high content of polyphenols and vitamins, are considered important sources of antioxidant compounds with strong health-promoting properties. However, among the different species belonging to the genus Vaccinium, a great morphological and biochemical variability can be found. Currently, in parallel with the development of genetic engineering, new eco-friendly technologies able to improve the nutraceutical quality of fruit and vegetables are emerging. Among these, the application of ultraviolet (UV)-B radiation of fresh plant-based food is very promising thanks to its ability to modulate many pathways involved in the biosynthesis of numerous beneficial secondary metabolites. The aim of the current research was to: 1) highlight differences in fruit quality between bilberry (Vaccinium myrtillus), that grows spontaneously in high mountain, and the most cultivated species, i.e., the blueberry Vaccinium corymbosum; 2) evaluate the effectiveness of post-harvest UV-B treatments in increasing the content of the main antioxidant compounds of the two species. Two experimental conditions were evaluated: 1) 12-h UV-B treatment (129.6 kJ m-2) followed by a 12-h recovery; 2) 18-h UV-B treatment (194.4 kJ m-2) followed by a 24-h recovery. V. myrtillus showed significantly lower dimensions and weight than V. corymbosum and, considering the color parameters (according to CIELAB system), it showed lower L* and higher a* and b* values. Besides, bilberries had a much higher content of total phenols, flavonoids and anthocyanins than cultivated blueberries, with a consequently higher antioxidant capacity. Following the UV-B treatments, no changes in weight or dimensions were detected. The exocarp color of V. myrtillus was unaffected by the treatment, while lower L* and b* values were observed in V. corymbosum fruit after the 18-h UV-B treatment (darker and bluer fruits). Blueberries showed a significant increase in total phenolic concentration in the 18-h UV-B-irradiated fruit, contrarily to what happened after the12-h UV-B exposure. The antioxidant activity was found to be generally in line with the variations of the total phenolics, flavonoids, and anthocyanins concentrations. These results showed that the variability in the organoleptic and biochemical profile between bilberry and blueberry species is extremely marked, and such genotypic differences reflect into the different responses to the postharvest supplementation of UV-B radiation. However, UV-B irradiation can be an effective tool to modulate the concentration of beneficial compounds for cultivated blueberry.