荔枝果肉不同酚类成分群的分离及其抗氧化活性

【目的】比较荔枝果肉不同酚类成分群的总酚、总黄酮和缩合单宁含量、单体酚组成及抗氧化活性差异,明确荔枝果肉中发挥抗氧化作用的有效酚类成分,为揭示荔枝果肉发挥健康效应的物质基础提供依据。【方法】利用C18硅胶层析柱将荔枝果肉多酚提取物分离成F1、F2、F3和F4共4个不同的酚类成分群,分析各成分群的总酚、总黄酮和缩合单宁含量及单体酚组成,采用铁离子还原能力(ferric reducing ability of plasma,FRAP)、1,1-二苯基-2-苦基苯肼(1,1-diphenyl-2-picrylhydrazy,DPPH)自由基消除能力、氧自由基吸收能力(oxygen radical absorbance capacity,ORAC)及细胞抗氧化能力(cellular antioxidant ability,CAA)4种抗氧化活性评价体系比较这4个成分群的抗氧化活性大小。【结果】荔枝果肉多酚提取物可以分为F1、F2、F3和F4共4个酚类成分群,其中F2的得率高达36%,其他成分群得率分别为18.71%、16.79%、21.12%;各酚类成分群的总酚、总黄酮和缩合单宁含量分别介于218.86—499.78 mg GAE·g~(-1) DW、414.94—1 285.45 mg RE·g~(-1) DW、83.35—483.43 mg CE·g~(-1) DW。4个成分群中F2的总酚、总黄酮和缩合单宁含量最高,对荔枝果肉多酚提取物相应的贡献率最大,分别为50.31%、54.24%、72.06%,均高于其余3个成分群的贡献率;其次是F3和F4;F1的最低。经HPLC分析和鉴定发现F2成分群主要为原花青素B2、表儿茶素等单体酚,F3仅含槲皮素-3-O-芸香糖-7-O-α-L-鼠李糖苷一种单体酚,F4中含有芦丁等。抗氧化活性评价结果显示,4个成分群的FRAP抗氧化能力大小顺序为F2F3F4F1;DPPH消除能力的IC50值分别为27.00、9.76、19.41和16.25μg·m L~(-1),其中F2的IC50值最小,即DPPH消除能力最强,其次是F4、F3,F1最弱;ORAC抗氧化能力顺序为F2F3F4F1,CAA抗氧化能力顺序为F2F3F4、F1,其中F2的ORAC和CAA抗氧化能力分别为8.36 mmol TE·g~(-1)DW和190.71μmol QE·g~(-1) DW,对荔枝果肉多酚提取物ORAC和CAA值的贡献率分别高达50.42%和84.91%。【结论】荔枝果肉4个酚类成分群间的总酚、总黄酮和缩合单宁含量及抗氧化活性均存在显著差异,各成分群的单体酚组成亦各有特点,其中F2成分群的得率及总酚、总黄酮和缩合单宁含量最高,抗氧化活性最好,是荔枝果肉抗氧化作用的最主要酚类物质。

Separation and Antioxidant Activity of Different Phenolic Compound Fractions from Litchi Pulp

【Objective】The total phenolics, total flavoniods and tannin content and antioxidant activity of different phenolic compound fractions from litchi pulp were compared to clarify the effective phenolic compounds of antioxidant activity from litchi pulp. The results of research will provide a basis for revealing the main compounds from litchi pulp to human health.【Method】Litchi pulp polyphenol extracts were divided into four phenolic compound fractions (F1, F2, F3 and F4) by C18 silica gel column. Then the total phenolics, total flavonoids and tannin content and the compositions of free phenol of four compound fractions were determined. Also, the FRAP, DPPH, ORAC and CAA antioxidation indexes were adopted to evaluate the antioxidant capacities of four different compound fractions.【Result】The results showed that litchi pulp polyphenol extracts were well-divided into four phenolic compound fractions. Among them, the yield of F2 was as high as 36%, and others’ were 18.71%, 16.79% and 21.12%, respectively. Total phenolics, total flavonoids and tannin content of four phenolic compound fractions ranged from 218.86 to 499.78 mg GAE/g DW, 414.94 to 1 285.45 mg RE·g^-1 DW and 83.35 to 483.43 mg CE·g^-1 DW, respectively. Among the four compound fractions tested, F2 exhibited the highest total phenolics, total flavonoids and tannin content with their corresponding percentage contribution as high as 50.31%, 54.24% and 72.06% to litchi pulp polyphenol extracts, followed by F3, F4, and finally F1. Procyanidin B2 and epicatechin in F2, quercetin-3-O-rutinoside-7-O-α-L-rhamnoside in F3 and rutin in F4 were identified by HPLC. The results of antioxidation indexes showed that FRAP values of four compound fractions were F2＞F3＞F4＞F1. The IC₅₀ values of DPPH free radical scavenging were 27.00, 9.76, 19.41 and 16.25 μg·mL^-1, respectively, then F2 exhibited the strongest DPPH free radical scavenging ability with minimum IC₅₀ value among the four compound fractions, followed by F4, F3, and finally F1. Also, the ORAC values of them were F2＞F3＞F4＞F1 and the CAA values were F2＞F3＞F4, F1. Among them, F2 exhibited the highest ORAC and CAA values as 8.36 mmol TE·g^-1 DW and 190.71 μmol QE·g^-1 DW with the percentage contribution as high as 50.42% and 84.91% to total ORAC and CAA values of litchi pulp polyphenol extracts, respectively.【Conclusion】These results indicated that there were significant differences in total phenolics, total flavonoids and tannin content and antioxidant activity among the four phenolic compounds fractions from litchi pulp. The compositions of each phenolic compound fraction were also different. What’s more, F2 exhibited the highest yield, total phenolics, total flavonoids and tannin content with the best antioxidant capacities. Interestingly, the phenolics in F2 may be the most main active compounds of antioxidant activity from litchi pulp.