Influence of UV-B Light Emitting Diodes on Colour Development and Accumulation of Polyphenols and Antioxidants in Apple Skin

UV light provoked stress can evoke antioxidant defence system and consequently induces the synthesis of several phytochemical compounds. The aim of the present study was to investigate the influence of UV-B light irradiation on surface colour and synthesis of some bioactive compounds in apples skin of cultivars ‘Elstar’ and ‘Jonagold’. Half of each apple was shaded with aluminium foil to compare irradiated and non-irradiated parts of skin. Apple fruits were exposed to constant UV-B light at 310 nm in chamber for 13 days at 8.5 °C. The UV-B light emitting diodes were positioned ca. 13 cm above the apple fruit and the average irradiance fruit received was 4.6 μW/cm2. Measurements of colour parameters (L*, a*, b*) were performed on the same spots of irradiated and non-irradiated surface of each apple fruit before and after 7, 10 and 13 days of storage constant UV-B light irradiation. All apple fruits started to develop red colour on the irradiated surface. The antioxidant potential, ascorbic acid content, total phenolic compounds, six flavonols and anthocyanin cyanidin-3-galactoside were quantitatively evaluated. Apple skins exposed to UV-B light irradiation contained significantly more total phenolic compounds and had higher antioxidant potential as compared to non-irradiated. UV light treated apple skin contained more cyanidin-3-galactoside and flavonols.