Comprehensive trait evaluation for kiwifruit nutritional quality

Abstract:【Objective】The evaluation on nutritional trait is an important procedure for kiwifruit breeding and comprehensive utilization. In order to provide technical support for comprehensive evaluation of kiwifruit nutritional traits, the nutritional quality indexes of kiwifruit were determined and the establishment of classification system was discussed in this study.【Methods】155 kiwifruit fruit samples from three major kiwifruit producing areas (Shanxi province, Sichuan province and Henan province) were collected in September, 2020. The cultivars of kiwifruit samples were Cuixiang, Hayward, Hongyang, Jintao, Jinyan and Xuxiang. Thirteen nutritional quality indexes including total soluble solids, total sugar, total acid, vitamin C, sucrose, glucose, fructose, citric acid, quinic acid, malic acid, total phenols, chlorophylls and carotenoids were determined after ripening and softening. A refractometer was used to determine the content of total soluble solids according to NY/T 2637—2014. Phenanthroline titration was used to determine total soluble sugar content. 2, 6-dichloroindophenol titration was used to determine vitamin C content according to GB 5009.86-2016. The method of NaOH neutralization was used for determination of total acid content according to GB/T 12456—2008. The content of organic acids was determined by Metrohm 861 IC according to NY/T 2796—2015. Sucrose, glucose and fructose contents were determined by Waters 2695-2489-2475 HPLC according to GB 5009.8-2016. Folin-ciocalteu colorimetry determination of total phenol was conducted according to NY/T 1600—2008. The total contents of chlorophylls and carotenoids were determined by colorimetry. The SPSS software was used to extract the representative indexes of kiwifruit nutritional quality evaluation by correlation and principal component analysis. The weight of representative indexes was by analytic hierarchy process (AHP). The index scoring standard and comprehensive evaluation system were determined by the probability classification analysis and the reasonable full- distance equal analysis.【Results】The variation range of kiwifruit nutritional quality indexes varied greatly, with the variation coefficient ranging from 14.68% to 112.94%. The sucrose value had the largest variation coefficient of 112.94%. However, the total acid and citric acid had a relatively lower variation coefficient, which was 14.68% and 15.85%, respectively. There was a significant correlation among the nutritional quality indexes. The total soluble solids had a very significant positive correlation to total sugar, sucrose, glucose and fructose contents (p＜0.01). There was a very significant positive correlation between total acid and citric acid content (p＜0.01). Vitamin C showed a very significant positive correlation to total sugar, glucose and total phenol content (p＜0.01). Four principal factors were extracted from the 13 indexes, which contributed to 38.59% , 13.77% , 12.71% and 11.31% of variation, respectively, with a cumulative percentage of 76.39%. The 1st principal component represented indexes including total soluble solids, total sugar, glucose, fructose and vitamin C, which reflected the sweet taste and functional characteristics of kiwifruit. And the 2nd principal component included total acid, citric acid and total phenol, which reflected sour taste and functional characteristics of kiwifruit. The third principal component included chlorophyll, which reflected the color characteristics of kiwifruit. The fourth principal component was carotenoids, which reflected the color and functional characteristics of kiwifruit. Four representative indexes (total soluble solids, total acid, vitamin C and carotenoids) were screened as evaluation indexes of kiwifruit nutritional quality by correlation analysis and AHP, which represented sweet index, sour index, nutritional function index and color function index, respectively. The total soluble solids had the greatest impact on the nutritional quality of kiwifruit, followed by total acid and vitamin C, and carotenoids had the least impact. The total soluble solids, vitamin C and carotenoid indexes were positive, however, total acid was a negative index. The four indexes were in line with normal distribution, and their weight coefficients were 56%, 20%, 20%, and 8%, respectively. These four indexes could be divided into 5 grades (lower, low, medium, high, and higher) and the scoring standards of them were also established. The scores of the four indexes from lower to higher were 10.4-52.0, 4.0-20.0, 4.0-20.0 and 1.6-8.0, respectively. The total score of each sample was the sum of the four index scores, and the full scores was 100. The 155 kiwifruit samples were divided into 3 grades, including super grade (＞70 scores), first grade (45-70 scores)and second grade (＜45 scores). There were 37 kiwifruit samples classified as second grade, 66 kiwifruit samples classified as first grade and 52 kiwifruit samples in super grade.【Conclusion】The representative indexes of comprehensive evaluation of kiwifruit nutritional quality were total soluble solids, total acid, vitamin C and carotenoids. The established four comprehensive nutritional quality scoring standards could be used for evaluation and classification of kiwifruit nutritional quality