Comparative analysis of fruit quality of five litchi cultivars

Abstract: 【Objective】Lychee (Litchi chinensis Sonn.) is a famous tropical fruit cultivated in south Chi-na. There are more than 40 varieties for commercial production. Huaizhi, Heiye and Feizixiao are most widely cultivated varieties. In recent years, many new cultivars with better quality has been bred. In this study four new lychee cultivars Xianjinfeng (XJF), Shuijingqiu (SJQ), Folü (FL) and Bingli (BL) were investigated to define their quality and flavor differences compared with the older cultivar Huaizhi (HZ).【Methods】The fructose, glucose and sucrose of the fruits were detected with Hexokinase and su-crose kit. Total soluble solids (TSS) were measured by a Brix meter (PAL-1). Acid components and vita-in C content were determined by High Performance Liquid Chromatography (HPLC) equipped with a C18 reverse chromatographic column and UV-detector. The total phenols and flavonoids were detected with Folin-phenol analysis kit (G0117W) and NaNO2- Al(NO3)3- NaOH colorimetric method kit (G0118W), respectively. The volatile flavor compounds were detected by Gas Chromatography-Ion Mo- bility Spectrometry (GC-IMS) technology with flavor analyzer instrument (FlavourSpec®, G.A.S). In-strument plug-in software VOCal with NIST and IMS database were used for identification and quantifi-cation of volatile flavor compounds. Plug in Gallery Plot and Dynamic PCA software were used for gen-erating fingerprint and clustering and similarity analysis for volatile flavor compounds.【Results】The  average TSS of the four new lychee cultivars were all slightly higher than that of HZ, with no signifi-cance. While the sugar composition and contents of new lychee cultivars were significantly different from those of HZ. The contents of glucose and fructose of XJF were 24.5% and 14.5% lower than that of HZ, and the content of sucrose was almost twice as high as that of HZ, and the contents of the three kinds of sugars were almost the same in XJF. The content of sucrose of SJQ, FL and BL cultivars was similar to that of HZ and were lower than the levels of glucose and fructose. The highest content of acid components was malic acid in all of the cultivars and was several to ten times higher than citric acid and succinic acid. XJF and HZ had the similar levels of malic acid content, the other three new lychee cultivars had much lower content of malic acid compared with HZ, FL had the lowest malic acid con- tent. The contents of citric acid of the four new lychee cultivars were all higher than that of HZ and they were in the order of BL>XJF>SJQ>FL. XJF and FL had higher contents of Vitamin C (254.3 and 299.8 µg·g^-1) than those of HZ (211.4 µg·g^-1), SJQ (153.8 µg·g^-1) and BL (133.5 µg·g^-1). The concentrations of total phenols and flavonoids in all cultivars were relatively lower and the difference between them was not obvious. The total 53 identified and 22 unidentified volatile flavor compounds of five lychee cultivars were detected by the technique of GC-IMS. The identified volatile flavor compounds included 11 kinds of aldehyde, 10 kinds of alcohol, 8 kinds of esters, 7 kinds of alkene, 6 kinds of ketones, 1 kinds of furan and 1 kinds of acid. The fingerprint information of volatile flavor compounds showed dif- ferent composition among cultivars. HZ, BL, XJF and SJQ had their specific characteristic fingerprint peak regions, whereas FL had no the peak region but had characteristic compounds of 1-hexanol, 2,3-pentanedione, 3-octanone and other two unidentified chemicals. About ten different volatile flavor com-pounds existed in each characteristic fingerprint peak region of BL, XJF and SJQ, but they were totally different each other and also different from HZ among identified chemicals and only two unidentified chemicals were the same between XJF and HZ, indicating the most important distinction among the dif- ferent lychee cultivars was volatile flavor compounds. The analysis of GC-IMS principal component analysis showed that five different cultivars were isolated clearly in five groups. The distance was near between BL and HZ and they were far from XJF. SJQ and FL were nearly located but they were the most far from HZ. The results indicated that the difference of volatile flavor compounds in BL and HZ were less than those of other cultivars and XJF had great difference copared with HZ and BL. Maxi-mum difference was found in SJQ and FL.【Conclusion】As shown above, compared with HZ, the fruit quality indexes of the four new lychee cultivars had some difference, respectively, but the difference of volatile flavor components was different significantly. It was suggested that the sugar and acid composi-tion and content, as well as volatile flavor compounds could be used as the quality evaluation indexes of new lychee cultivars.