Effect of blue LED light irradiation on anthocyanin synthesis in the skin of detached apples

This study aimed to improve the marketability of poorly colored apples by increasing the anthocyanin concentration in the skin of fruit using blue LED light irradiation. Apple samples were collected at commercial harvest time from Morioka, a cold region in Japan. To determine the suitable temperatures for anthocyanin synthesis in the skin of apples, fruit were irradiated with blue LED lights in incubators at 11, 15 and 20°C for four days. For ‘Tsugaru’ and ‘Shinano Sweet’ apples, more anthocyanin accumulated under higher temperature conditions. Whereas for ‘Jonagold’ and ‘Fuji’ apples, anthocyanin levels were similar for all three temperature conditions. Therefore, in terms of improving apple pigmentation and maintaining firmness, irradiation at 15°C is preferred. The irradiation equipment used was adjusted to 15°C through a vent system when placed in the refrigerator. The 1-methylcyclopropene (1-MCP) treatment of ‘Shinano Sweet’, ‘Jonagold’ and ‘Fuji’ apples did not influence anthocyanin accumulation or fruit firmness. The skin of the apples after irradiation at 15°C for four days with blue LED light showed improved fruit skin pigmentation. However, it did not affect fruit firmness regardless of 1-MCP treatment. Blue LED light irradiation was effective for anthocyanin accumulation in ‘Fuji’ apples harvested from different production areas (cold and warm regions) in Japan.