Effect of maturity stage at harvest on antioxidant capacity and total phenolics in kiwifruits (Actinidia spp.) grown in Korea

Six cultivars of kiwifruits grown in Korea, including Actinidia eriantha ‘Bidan’, A. arguta ‘Chiak’, A. arguta ‘Darae No. 2’, A. chinensis ‘Haegeum’, A. chinensis ‘Haehyang’, and A. arguta × A. deliciosa ‘Mansoo’, were harvested at various maturity stages to test whether kiwifruit maturity has an influence on antioxidant capacity or total phenolic and flavonoid contents. Kiwifruit extracts were isolated using absolute methanol and then 80% (v·v -1 ) aqueous methanol during homogenization. ‘Bidan’, collected at the second harvest stage, contained the greatest amount of total phenolics (775.3 mg gallic acid equivalents·100 g -1 fresh weight) and had the highest antioxidant capacity [816.5, 633.2, and 2,662.7 mg vitamin C equivalents·100 g -1 fresh weight for 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) scavenging, 1,1-diphenyl-2-picrylhydrazyl scavenging, and oxygen radical absorbance capacity assays, respectively] among cultivars tested, while ‘Haehyang’, collected at the first harvest, contained the greatest amount of total flavonoids (13.1 mg catechin equivalents·100 g -1 fresh weight). Kiwifruit cultivar and genotype influenced antioxidant capacity, as well as total phenolic and flavonoid contents. No trend, however, was observed in total phenolic and flavonoid contents, and in the antioxidant capacity with respect to maturity stage. Antioxidant capacity had a higher linear correlation coefficient with total phenolic contents than with total flavonoid contents. The results above suggest that kiwifruits at various maturity stages are a valuable source of phenolics and antioxidants for industrial application and consumer health benefit.