优新荔枝品种果实品质风味特征比较

Comparison on Fruit Quality and Flavor of New and Fine Litchi Cultivars

明确华南5个优新荔枝品种果实品质风味特征的差异,为荔枝的品质评价、果品加工和产业优化提供科学依据。通过测定荔枝果肉糖酸组分和游离氨基酸含量,比较不同品种果实品质和风味差异。结果表明:桂味、仙进奉和井岗红糯为糖分均衡累积型品种,妃子笑和糯米糍分别为还原糖和蔗糖累积型品种。5个荔枝品种均主要累积苹果酸,酒石酸次之;最主要的游离氨基酸为γ-氨基丁酸(GABA)或丙氨酸(Ala)。甜味贡献最大的均是果糖,氨基酸中均以Ala、谷氨酸(Glu)和缬氨酸(Val)分别对甜味、鲜味和苦味的贡献最大,酒石酸则是酸味的最大贡献者,GABA对涩味贡献极大。荔枝品种间果肉甜度、甜度/总酸、总糖/总酸、甜味/鲜味氨基酸和甜味/苦味氨基酸均差异显著(P<0.05)。用上述指标评价5个荔枝品种的品质风味,评价结果差异大。不同品种荔枝果实风味物质含量差异显著。果糖、Ala、Glu、Val、GABA和酒石酸是荔枝果实独特风味的关键物质基础。

Sugar,organic acid and free amino acid are vital indicators not only for fresh fruit,but also for fruit processing.The profile of sugar and organic components,and free amino acids for five traditionally fine and new litchi(Litchi chinensis Sonn.)cultivars including Guiwei,Feizixiao,Nuomici,Xianjinfeng and Jingganghongnuo were investigated,and then the characteristics of fruit quality and flavor were compared among cultivars,with the target to promote fruit quality evaluation,fruit processing and industry optimization in litchi.Twenty two litchi orchards in the main production areas of Guangdong,Guangxi and Fujian were selected,where total 52 matured fruit samples from 5 litchi cultivars were collected.All flesh of matured fruit samples that peeled off peels and seeds,soaked in liquid nitrogen,ground into pulp by a mill and store for later determination.High performance liquid phase(HPLC)method was used to determine sugar and organic acid components.Ninhydrin post column derivatization method was adopted to analyze amino acid profile by automatic amino acid analyzer(8800 Hitachi).Further,the quality and flavor of the five cultivars were com pared.The results showed that glucose,fructose and sucrose were determined as the sugar components of litchi.Among them,'Guiwei','Xianjinfeng'and'Jingganghongnuo'belonged to sugar component balanced cultivars,however,'Feizixiao'and'Nuomici'were identified as reducing sugar accumulation type and sucrose accumulation type,respectively.Besides,by comparing the sugar content of different cultivars,the three sugar components of each cultivar could be perceived by humans.Three sugar components of all varieties can be perceived.Nine kinds of organic acids were observed in all litchi cultivars.Malic acid was the main organic acid component,followed by tartaric acid or acetic acid,and maleic acid was the minimum.However,only a small amount of samples in all litchi cultivars could detect low content of maleic acid,and most of them were not detected.Litchi fruits contained 30 free amino acids,and gamma-aminobutyric acid(GABA)or alanine(Ala)was the maximum ingredients.There were significant differences for the contents of sugar and organic acid components,free amino acids(with the exception of asparagine(Asn),glutamate(Glu)and cysteine(Cys))and taste amino acids(with the exception of umami amino acids)among cultivars(P<0.05).The contents of total organic acid and most organic acid components,total free amino acids,sweet and bitter amino acids in'Feizixiao'are significantly higher than those in all the other four cultivars.Fructose was the greatest contributor to sweetness of litchi fruit,irrespective of cultivars,with significant higher contribution values than those of the other two sugar components(P<0.01).The contribution of sweet amino acids to sweetness of litchi fruit was much lower than that of the three sugar components,but Ala contributed most to the sweetness among free amino acids.The most contributors of umami and bitter tastes were Glu and valine(Val),and tartaric acid was the greatest source of sourness taste.What's more,GABA contributes greatly to astringency.Since significant differences in sweetness values,sweet/sour ratios,sugar/acid ratios,umami/sweet amino acid ratios and sweet/bitter amino acid ratios were observed among cultivars(P<0.05),the quality and flavor of the five cultivars considerably differed by these indexes.In conclusion,the contents of various flavor substances in litchi fruits of the five cultivars are significantly different.Fructose,Ala,Glu,Val,GABA and tartaric acid are the key ingredients for the unique flavor of litchi fruits.Great variation is found in the quality and flavor of litchi cultivar as assessed by different evaluation indexes.It shows that it is still necessary to investigate the typical evaluation indicators for litchi in the future.