Nicotinamide Pre-treatment Shows a Protective Effect and Reduces UV-Induced Oxidative Stress in Raspberry Fruit

UV irradiation is a promising technology for extending the shelf life of soft fruit, including raspberry fruit. However, UV treatment, like all alternative post-harvest technologies for eliminating microbial load based on pro-oxidative properties, can negatively affect the redox status of fruit, paradoxically intensifying negative biochemical changes in the tissue and thus deteriorating fruit quality. In this study, it was examined whether nicotinamide treatment could protect raspberries against oxidative stress and energy metabolism disturbances induced by UV-C radiation. For this purpose, raspberry fruit was sprayed with an aqueous nicotinamide solution (10 mmol L⁻1), exposed to UV-C, and stored for 5 days at 4 °C. The results showed that nicotinamide reduced reactive oxygen species accumulation in UV-C- treated fruit and triggered multiple metabolic adjustments. Nicotinamide application was associated with enhanced mitochondrial activity, reflected by increased expression and activity of mitochondrial enzymes as well as higher ATP content. In addition, nicotinamide-treated fruit displayed improved redox balance, evidenced by elevated NADPH levels and enhanced activity of the glutathione and ascorbic acid biosynthesis pathways. Importantly, the use of nicotinamide had no significant effect on aroma compounds or on yeast and mold contamination, although it did reduce fructose content and increase glucose content. These findings provide new insights into the potential of nicotinamide as a postharvest treatment and underscore the central role of mitochondrial energy metabolism in maintaining the quality of soft fruit.