Establishment of comprehensive evaluation system for fruit quality of Zhongmi No. 2 kiwifruit from different regions of China

Abstract: 【Objective】The present experiment was undertaken to assess fruit quality of Zhongmi No. 2 from different regions of China and establish the comprehensive evaluation system for fruit quality. 【Methods】Zhongmi No. 2 fruit samples from 12 provinces were selected as experimental materials. Single fruit weight was measured using an electronic balance. The vertical and horizontal fruit diameters were measured with a vernier caliper, and the fruit shape index was calculated using the formula of fruit vertical diameter/horizontal diameter. The fruit firmness was determined by the digital display penetrometer GY-4-J. Soluble solids content and titratable acids were determined by the digital sugar and acid meter (PAL-BXIACID8 Master Kit, ATAGO). The internal quality indexes, including vitamin C, fructose, glucose and sucrose contents were determined with the national standard GB 5009.86—2016, and the tannin content was determined with the industry standard NY/T 1600—2008. The correlation of fruit quality indexes was analyzed to identify the relationships among different indexes using SPSS software. Principal component analysis of fruit indexes was conducted by SPSS software, and principal component was extracted based on the criterion of feature values greater than one. The 15 fruit index data were standardized as X1, ……, X15, which multiplied the feature vectors with the standardized datato obtain the score expressions of the 5 principal components. The comprehensive evaluation equation of fruit quality was established using the principal component variance contribution rate as the weight. 【Results】There were differences in the appearance quality indexes of Zhongmi No. 2 in different regions of China. The single fruit weight of Sichuan Zhongmi No. 2 was the smallest, while Shanghai was the biggest. The average single fruit weight was 110.07 g, with a coefficient of variation of 12.34%. The coefficient of variation for fruit vertical diameter, horizontal diameter and fruit shape index were 4.8%, 7.66% and 6.28%, respectively, indicating that the single fruit weight and fruit shape were less affected by regional differences. There were differences in fruit firmness among different regions, with a variation range of 0.54-1.36 kg·cm-2 and a coefficient of variation of 21.37%, which indicated the firmness was more easily affected by different regions compared to single fruit weight and fruit shape, but the coefficient of variation was still less than 30% that was relatively stable within a reasonable degree of dispersion. In summary, the appearance quality of Zhongmi No. 2 fruit was less affected by different regions, indicating its appearance had strong adaptability to different ecological environments. The average value of soluble solid content of Zhongmi No. 2 fruits from different regions of China was 18.14% with the coefficient of variation of 10.26%, and dry matter content was 20.15% with the coefficient of variation of 8.38%, indicating that soluble solid content and dry matter content were little influenced by regions, and the soluble solid content of Zhongmi No. 2 was stable in different areas. The range of titratable acid was 0.36%-1.25% with the coefficient of variation of 36.84%, which indicated that the acidity was easily affected by different regions. Vitamin C is the characteristic indicator of kiwifruit. The average value of Vitamin C of Zhongmi No. 2 was 102.51 mg·100 g-1 , and Vitamin C content was the highest in the fruit of Yunnan (altitude 1840 m), with the value of 131 mg·100 g-1 , while it was the lowest in the fruit of Jiangxi (altitude 22 m), with the value of 71.73 mg · 100 g- 1 , implying Vitamin C might be more accumulated in high altitude regions. Tannin is the main source of fruit astringency. The average tannin content of Zhongmi No. 2 from different regions of China was 787.75 mg·kg-1 with a coefficient of variation of 13.76%, indicating that tannin content was little influenced by different regions. Fructose, glucose and sucrose are the main soluble sugars of fruits. The average values of fructose and glucose of Zhongmi No. 2 were 4.69 mg·100 g-1 and 4.75 mg·100 g-1 respectively in different regions with similar content, and coefficient of variations were 18.02% and 19.99%, close to each other, while the average value of sucrose content was 1.60 mg·100 g-1 with a coefficient of variation of 65.94%. This suggested fructose and glucose were main soluble sugars of Zhongmi No. 2 with stable performance in different regions, while sucrose content was relatively low and highly susceptible to regional influences. The results showed that there were high correlations among fruit quality indexes of Zhongmi No. 2 in different regions, and those that were significantly relevant can be screened to simplify the evaluation system. Five principal components were extracted with the standard of eigenvalue greater than 1. Fructose, Vitamin C, firmness, tannin content and horizontal diameter were the first, second, third, fourth and fifth principal component, respectively. The first, the second and the fourth principal components represented the internal quality of the fruit, and the third and the fifth principal components represented the external quality of the fruit. The 15 fruit indexes of Zhongmi No. 2 were standardized, and a comprehensive evaluation formula (Fcom.= 0.395F1 +0.163F2 +0.157F3 +0.104F4 +0.725F5) for fruit quality using the principal component variance contribution rate as the weight was established. Based on the formula, the comprehensive scores of fruit quality in 12 provinces were: Chongqing, Shandong, Shanghai, Guizhou, Zhejiang, Yunnan, Sichuan, Hunan, Jiangxi, Jiangsu, Henan and Hubei. The higher the comprehensive score, the better the comprehensive quality of Zhongmi No. 2 in the region.【Conclusion】Zhongmi No. 2 has strong adaptability and can be promoted for planting in different ecological regions.