Dynamic changes and evaluation of fruit quality during on-vine ripening in Ganlü No. 1 kiwifruit (Actinidia eriantha)

Abstract: 【Objective】The present experiment was undertaken to explore the dynamic changes in the appearance and intrinsic quality of Ganlü No. 1 (Actinidia eriantha) fruit on different on-vine ripening times, comprehensively evaluate the fruit quality on different times, and identify the best time for onvine ripening. Kiwifruit is a respiratory climacteric fruit, which is easy to soften and decay after maturity and has a short edible window period. The on-vine fruit is still a living organism, and it will generally undergo physiological maturity on the vine and then fully mature with the best taste. The methods of onvine ripening can improve the fruit flavor. Ganlü No. 1 fruit has the characteristics of not being easy to drop after physiological maturity. So, it was used to explore new storage methods for kiwifruit.【Methods】The fruits of Ganlü No. 1 were collected from the physiological maturing stage (SSC ≥ 6.5%) (October 26, 2022) until the fruits were too ripen to be edible, with a total of six times: 171, 180, 192, 201, 210 and 222 days after full bloom (DAFB). The changes in hardness, color, ascorbic acid, titratable acid, soluble sugar, soluble solids, chlorophyll and carotenoids were measured, and the best time for onvine ripening was evaluated by the principal component analysis.【Results】During the on-vine ripening period, the Ganlü No. 1 fruit surface gradually smoothed, the color of the fruit surface became deepenedbrown, and the exocarp began to lose water and shrink on 222 DAFB. The whole flesh was tender greenon 171 DAFB, and the color of the flesh near the core began to change from tender green to dark green on 180 DAFB and gradually spread to the exocarp until the whole flesh turned dark green on 222 DAFB, and the flesh gradually became transparent. The core color gradually turned yellow, from light green to pale yellow. The flesh’s L* and b* values showed an overall decreasing trend. Notably, the b* value showed a significant decrease, dropping from its highest value of 27.81 on 171 DAFB to the lowest value of 9.79 on 210 DAFB, a reduction of 64.8% . The L* value also showed a significant decline from its highest value of 56.99 on 171 DAFB to the lowest value of 40.32 on 210 DAFB, representing a reduction of 29.25%. This indicated a decline in brightness, with the color becoming darker and more yellowish. Conversely, the a* value showed an overall increasing trend, from its lowest value of -11.7 on 171 DAFB to its highest value of 3.09 on 210 DAFB, representing a change of -126.41%. This increase signified a deepening of the red hue in the flesh. These changes in chromatic aberration values were consistent with the observed fruit appearance. The fruit shape index, single fruit quality and hardness showed a decreasing trend. The pulp hardness decreased significantly from the highest value of 155.61 g on 171 DAFB to the lowest value of 14.76 g on 210 DAFB, a decrease of 90.51%. The contents of ascorbic acid, titratable acid, soluble solids, soluble sugars and pigments increased first and then decreased. The content of AsA increased from 947.89 mg·100 g-1 on 171 DAFB to its highest value of 1 282.22 mg·100 g-1 on 192 DAFB with an increase of 24.12%, decreased to 905.17 mg · 100 g-1 on 201 DAFB with a decrease of 29.41%, increased to 1 028.95 mg · 100 g-1 on 210 DAFB, and decreased to its lowest value of 897.66 mg · 100 g- 1 on 222 DAFB. The titratable acid content increased slowly without significant difference from 171 DAFB to 180 DAFB, but from 180 DAFB to 192 DAFB, it increased significantly to its highest value of 1.26% on 192 DAFB. From 192 DAFB to 210 DAFB, it slowly decreased to 1.21% on 210 DAFB. However, from 210 DAFB to 222 DAFB, it declined sharply to its lowest value of 1.02% on 222 DAFB, a decrease of 15.7%. The contents of soluble solids and sugars showed an increased trend from 171 DAFB to 210 DAFB, reached their highest value on 210 DAFB, and then decreased rapidly. Notably, the soluble solids content increased significantly from its lowest value of 7.46% on 171 DAFB to its highest value of 18.41% on 210 DAFB, an increase of 146.78%. The soluble sugar content also increased significantly from its lowest value of 6.42% on 171 DAFB to its highest value of 10.87% on 210 DAFB, an increase of 40.94%. The contents of chlorophyll a, b and carotenoids all showed the“decreasing-increasing-decreasing”trend, and the overall trend decreased. From 180 DAFB to 201 DAFB, they increased significantly to 2.73, 1.68 and 1.62 mg·100 g- 1 on 201 DAFB, an increase of 52.51% , 37.93% and 44.64% , respectively. From 210 DAFB to 222 DAFB, they decreased sharply to their lowest value of 1.48, 0.77 and 0.92 mg · 100 g- 1 on 222 DAFB, a decrease of 45.79%, 61.5% and 43.21%, respectively, and the rate of decline showed chlorophyll b＞chlorophyll a＞carotenoids. Principal component analysis was carried out on six quality indexes of Ganlü No. 1 on six on-vine ripening times, and three principal components were extracted, with a cumulative contribution rate of 98.143%. The variance contribution rate of the first principal component was 50.52%, in which indexes of positive load were soluble sugar content (0.895), titratable acid content (0.731) and soluble solid content (0.935), and index of negative load was pulp hardness (-0.741), with all of indexes having high absolute loads. The variance contribution rate of the second principal component was 27.59%, and the total chlorophyll and carotenoid contents (0.766) had a high positive load. The variance contribution rate of the third principal component was 20.034% , and the ascorbic acid content (0.898) had a major positive effect. According to the comprehensive score of principal components, 192 DAFB had the highest comprehensive quality score of 1.112. 210 DAFB and 201 DAFB were list-ed second and third, respectively. 180, 171, 222 DAFB ranked 4-6 in sequence.【Conclusion】During the on- vine ripening period of Ganlü No. 1 fruits, the appearance indexes showed a decreasing trend, and the intrinsic quality showed a trend of first ascending and then descending. The content of AsA reached a peak of 1 282.22 mg · 100 g-1 on 192 DAFB, and the content of soluble sugar reached a peak of 10.87% on 210 DAFB. The comprehensive evaluation of principal component analysis showed that the comprehensive quality of the fruit was the best after 21-39 days during the on-vine ripening period.