Comprehensive evaluation of fruit quality of Baitangying litchi based on principal component analysis

Abstract:【Objective】The fruit quality of litchi varies among different production areas. However, few literatures report the comprehensive evaluation of the fruit quality of the same cultivar from different or-chards. Understanding the fruit quality traits can provide breeders with valuable information and assess-ment tools. The composition and content of soluble sugars, organic acids and other quality indexes of Baitangying fruit from 20 different orchards were analyzed from 2020 to 2021. The aim of this study was to explore the comprehensive fruit quality traits and differences of Baitangying litchi in Maoming.【Methods】A total of 28 litchi samples were collected from the demonstration orchards and some large orchards in Maoming, Guangdong. To explore the fruit quality traits, we measured twenty parameters including titratable acid, total soluble solid (TSS), average weight, flesh recovery, fructose, glucose, su-crose, percentage of sucrose against total sugar, percentage of reducing sugar against total sugar, (fruc-tose +glucose)/ sucrose, ratio of fructose to glucose, ratio of TSS to titratable acid, ratio of total sugar to total organic acid, and malic acid, citric acid, ascorbic acid, and total organic acid content. SPSS20.0 sta-tistical software was used for coefficient of variation (CV) analysis, correlation analysis, principal com-ponent analysis (PCA), stepwise regression analysis, and comprehensive score ranking to analyze and evaluate the litchi fruit quality of different orchards.【Results】The results showed that the litchi fruit quality traits of different orchards were different, with the CV ranging from 3.74% to 81.63%. The CV of total soluble solid, average fruit weight, flesh recovery and soluble sugar of the 28 litchi samples were smaller (3.74%-10.29%) than that of the rest fourteen indexes (12.81%-81.63%). Orchard cultiva-tion and management practices, microclimate conditions, and other factors were the main reasons for the differences. The correlation between different indexes was analyzed. Correlation analysis results showed there were extremely significant or significant correlations among titratable acid content, sugar to acid ratio, sweetness, ascorbic acid, and soluble sugar. There were extremely significant or signifi-cant correlations between similar indexes (such as sugars, organic acids, etc.). It reflects the consistency of genetic characters of Baitangying litchi in the same region, and also reflects that there are same differ-ences in some of indicators such as fruit appearance due to different cultivation and management tech-niques. Sucrose significant influenced the sweetness of Baitangying litchi; malic acid significantly influ-enced the sourness. Climate, geographical conditions, phenology and cultivation management practices of different producing areas affected sugar content, but did not change sugar composition. Twenty litchi characters and nutritional components were analyzed by principal component analysis. Four principal components with characteristic roots greater than 1 were extracted by PCA, and the cumulative contri-bution rate was 85.226% . The first principal component explained 33.746% of the trait information which had high correlations with total sugar, sweetness, sucrose, TSS, glucose, and fructose. The first principal component was related to the total sugar content of fruit. The second principal component ex-plained 27.996% of the trait information that had high a correlation with titratable acid. The third princi-pal component showed high correlations with the ratio of fructose to total sugar and the ratio of fructose to sucrose, and could explain 15.585% of the trait information. The fourth principal component ex-plained 7.898% of the trait information related to total organic acid. Based on the component scoring co-efficient matrix, the score of each sample on the corresponding principal component was obtained. The four principal components reflected total sugar, titratable acid, reducing sugar, and fruit total organic ac-id factors, respectively. The PCA method avoided subjective influence of artificial evaluation on evalua-tion of fruit quality. Taking the comprehensive factor score of Baitangying litchi sample obtained by principal component analysis as the dependent variable and the quality indexes involved in the four prin-cipal components as the independent variables, stepwise regression analysis was carried out to establish the theoretical prediction model of litchi quality, which was established with four effective indexes sort-ed as sum of sweetness, malic acid, titratable acid, and ascorbic acid.【Conclusion】Sweetness, malic ac-id, titratable acid, and ascorbic acid are important factors to evaluate the fruit quality of Baitangying li-tchi. The contents of soluble sugar and various organic acids in litchi are an important factor affecting the taste and flavor.