Dynamic changes in total phenols, flavonoids and antioxidant capacity during fruit development of different kiwifruit cultivars

Abstract: 【Objective】Phenolics are rich in kiwifruit, especially in the fruit of Actinidia eriantha, butthere is not much research on this. The main aim of this study was to discover and analyze the dynamicchanges in the contents of total phenols, flavonoids and the antioxidant activity during the fruit develop-ment in different kiwifruit cultivars. At the same time, the relationship of the contents of total phenolsand flavonoids with antioxidant capacity was analyzed.【Methods】'Jinkui' (A. deliciosa) and'Hong-yang' (A. chinensis) , the two main cultivars in Jiangxi, and'Ganmi-6' (A. eriantha) , a new cultivarbred by our group, were selected as materials. Not less than 30 fruit with the same shape and uniformsize were randomly collected from the south side of the tree crown of the three cultivars every 15 daysfrom 30 d after blooming until the fruit ripened at 165 days after blooming. All the fruit were put in iceboxes and immediately brought back to the lab to test the contents of total phenols and flavonoids, theFRAP antioxidant ability and the scavenging capacity of hydroxyl radical (· OH) , 1, 1-dipphenyl-2-pic-rylhydrazyl radical (DPPH ·) and superoxide anion radical (· O2-) during the fruit development. The dif-ferences in the contents of total phenols and flavonoids as well as antioxidant capacity in all tested threecultivars were compared, and the correlation of the contents of total phenols and flavonoids with antioxi-dant capacity were analyzed.【Results】The results indicated that the contents of total phenols and flavo-noids in all the tested cultivars showed a similar change trend from high to low during fruit develop-ment. However, there were significant differences in the contents of total phenols and flavonoids in dif-ferent cultivars. The content of the total phenols in'Ganmi-6'was more than ten times higher than inthe other two cultivars. During the fruit development, the lowest content of total phenols in'Ganmi-6'was 4 660.6 mg · kg-1, while the maximum total phenol content in' Jinkui'was 2 457.6 mg · kg-1 and2 143.3 mg · kg-1 in'Hongyang'. Content of flavonoids was lowest in mature fruit, which was 235.7 mg · kg-1, 190.0 mg · kg-1 and 173.1 mg · kg-1 in the fruit of' Ganmi-6', ' Jinkui'and' Hongyang', respectively. The results of antioxidant activity showed that the FRAP antioxidant ability decreasedwith the ripening of the fruit in'Hongyang', but it fluctuated in the fruit of'Jinkui', and the FRAP an-tioxidant ability at the ripening stage was lower than that of the young fruit. However, the FRAP antioxi-dant capacity of'Ganmi-6'in the whole process of fruit growth remained high with the FRAP value inthe range of 786.5 mg · kg-1-838.2 mg · kg-1, which was significantly higher than that in the other twocultivars from 90 days after blooming. Although the scavenging capacity of DPPH · in the fruit of'Gan-mi-6'was at a higher level, there was a slow change from low to high during the fruit development inthe three tested cultivars. The scavenging capacity of · OH in the fruit of'Jinkui'and'Hongyang'fluc-tuated slightly and the value of the ripe fruit was slightly lower than that of the young fruit. However, the scavenging capacity of · OH in the fruit of'Ganmi-6'gradually increased, and the value of 71.40%at 165 d after blooming was significantly higher than the value of 27.82% at 30 d after blooming. Thescavenging capacity of · O2-in the fruit of'Jinkui'and'Hongyang'changed gently during the earlystage of fruit development, then slightly declined at the middle stage of fruit development, and rose ob-viously at the ripe stage. The scavenging capacity of · O2-in the fruit of'Ganmi-6'gradually declined, and the value of 52.08% at 165 d after blooming was significantly lower than 65.29% at 30 d afterblooming. The result of the scavenging capacity of · O2-also showed that'Ganmi-6'had stronger anti-oxidant ability than the other two cultivars. Correlation analysis revealed that there were extremely sig-nificant positive correlations between · O2-scavenging capacity and the contents of total phenols and fla-vonoids, and significant positive correlations between · OH scavenging capacity and the contents of to-tal phenols during the'Ganmi-6'fruit development. During the'Jinkui'fruit development, there werealso significant positive correlations between the FRAP antioxidant ability and the contents of total phe-nols and flavonoids. Significant positive correlations were also found between the FRAP antioxidantability and the contents of total phenols and flavonoids in'Hongyang'. In addition, there were extreme-ly significant positive correlations between DPPH · scavenging capacity and the contents of total phe-nols and flavonoids during the'Hongyang'fruit development.【Conclusion】The contents of phenolicswere high in the three tested kiwifruit cultivars and gradually decreased during the fruit development.The contents of total phenols and flavonoids were significantly correlated with the fruit antioxidant ca-pacity. However, the contents of phenolics and the antioxidant capacity were significantly differentamong cultivars.'Ganmi-6'had higher phenolics contents and stronger antioxidant capacity than'Jinkui'and'Hongyang'.