Study on fruit peeling characters of different kiwifruit varieties

Abstract:【Objective】Actinidia chinensis var. chinensis and A. chinensis var. deliciosa are the main types of commercially cultivated kiwifruit at present, the inconvenience of peeling and eating both hinder consumer’s choice of kiwifruit. Some varieties of kiwifruit, such as A. eriantha generally has the characteristics of easy peeling, however, there is no comprehensive and objective evaluation system for the description of the peeling traits of different kiwifruit varieties. In this study, we compared the changes of fruit peeling traits of different kiwifruit varieties at soft ripening stage and established a comprehensive evaluation system of kiwi-fruit peeling traits to objectively reflect the difference of fruit peeling difficulty among different kiwifuit varieties, which would lay a theoretical foundation for further research on the physiology and molecular mechanism of kiwi-fruit peeling.【Methods】Twenty-five kiwifruit varieties were used as materials, including 16 A. chinensis var. chinensis varieties, 4 A. chinensis var. deliciosa varieties, and 5 A. eriantha varieties. The“peeling number”,“peeling degree”and“peeling force”of each kiwifruit variety were tested respectively. The number of peeling refered to the number of skins removed from the whole fruit by manual tearing from the stylar end to the stalk end. Thepeeling degree was evaluated by assigning scores, which were divided into 5 grades according to peel and pulp peel degree (unable to peel at all, more difficult to peel, difficult to peel, easier to peel, easy to peel). Combined with the kiwifruit stripper based on the mechanical measuring device, the peeling force of each kiwifruit was determined by measuring the force in four directions of the fruit and calculating the average value. Then the evaluation system of kiwifruit peeling traits was established by synthesizing the three indexes, and the differences of peeling traits among different kiwifruit varieties were compared.【Results】The peel number of A. eriantha was significantly less than those of A. chinensis var. chinensis and A. chinensis var. Deliciosa, and the peeling degree evaluation grade was significantly higher than those of the two varieties, indicating that A. eriantha was easier to peel and had better peeling property than the other two kiwifruit varieties. However, the peeling force of A. eriantha was not the smallest, and the peeling power of A. chinensis var. chinensis and A. chinensis var. Deliciosa was even lower than that of A. eriantha. Therefore, by comprehensively comparing the fruit peeling number, peeling degree and peeling force of different varieties of kiwifruit, three indexes were obtained: Among the 16 varieties of A. chinensis with the same fruit size, Jinfeng had less peeling times (18 times) than other varieties, the highest peeling degree was 3-4 points, and the pulp damage degree was lower, followed by Jin Feng, in the case of little difference in peeling number and peeling degree with other varieties, the average peeling force required was 0.42 N, which was the smallest. Among the 4 varieties of A. chinensis var. deliciosa with the same fruit size, Miliang No. 1 had little difference in the peeling number and peeling degree compared with the other varieties, but the average peeling force required was only 0.38 N, the peel was easier to peel, and the pulp was less damaged, although 20 times of the peeling number of Guichang was the least, but the required peeling force was 1.20 N, the peel was also more difficult to peel. Among the 5 varieties of A. eriantha with the same fruit size, Ganlü No. 1 had at least 7 peeling times compared with the others, and the highest peeling degree was 7-8 points, and Ganlü 6 had the peeling degree 5-6 points, the highest peeling number (13 times) and was relatively difficult to peel compared with the others. In summary, there were great differences in the peeling traits of different kiwifruit varieties. Among the 25 kiwifruit varieties, Ganlü No. 1 had the lowest peeling number, the highest peeling degree, and the lower peeling force, second only to the lowest Jin Feng and Milang No. 1, and it was the easiest to peel according to the evaluation of three indexes. The peeling number of Donghong and Hongshi No. 2 was as high as 49 times and 52 times, the peeling degree grade was 0, the average peeling force required was 1.68 N and 1.59 N, significantly higher than those of the other kiwifruit varieties, so both were not easy to peel.【Conclusion】The fruit peeling characters of different kiwifruit species were different. At the same time, different varieties of the same kind of kiwifruit peeling characters also had great differences. By comprehensively comparing the fruit peeling number, peeling degree and peeling force of each variety of kiwifruit, among the 25 kiwifruit varieties, Ganlü No. 1 had the lowest peeling number, the highest peeling degree evaluation grade, and the smallest peeling force, so it was the easiest to peel.