5种籼稻品种谷壳中游离态和结合态酚类物质含量及其抗氧化活性比较

【目的】比较不同水稻品种谷壳中游离态和结合态酚类物质的含量、组成及其抗氧化活性差异。【方法】选用5个代表性的南方籼稻品种，分析其谷壳中的游离态和结合态总酚、总黄酮含量，采用高效液相色谱法分析其单体酚类的组成及含量，采用铁离子还原能力（FRAP, Ferric reducing ability of plasma）和ABTS(2,2''-联氨-二-3-乙基-苯并噻唑-6-磺酸，2, 2′-azino-bis-3-ethylbenzothiazoline-6-sulphonic acid)自由基清除能力两种方法评价其体外抗氧化能力差异。【结果】 5个不同籼稻品种谷壳的游离酚、结合酚和总酚含量分别介于42.8—123.0、260.9—325.2和320.2—398.3 mg GAE/100 g DW，其结合态酚占总酚含量百分比平均为78.9%；游离态黄酮、结合态黄酮和总黄酮含量分别介于34.0—58.0、47.9—64.4和82.0—115.7 mg CE/100 g DW，其结合态黄酮占总黄酮含量的百分比平均为56.4%；稻壳中的酚类物质主要为没食子酸、原儿茶酸、绿原酸、香草酸、咖啡酸、丁香酸、香豆酸和阿魏酸，其中游离态酚类物质以丁香酸和香豆酸为主，平均含量分别为25.09 μg?g-1 DW和31.21 μg?g-1 DW；结合态酚类物质以香豆酸含量为主，平均含量为2141.61 μg?g-1 DW。稻壳游离态、结合态和两者合计FRAP抗氧化能力值分别介于37.7—106.0、217.9—281.0和269.3—370.3 mg TE/100 g DW，其结合态占总FRAP百分比平均为77.3%；稻壳游离态、结合态和两者合计ABTS抗氧化能力值分别介于26.3—85.8、67.2—111.9和93.4—155.2 mg TE/100 g DW，其结合态占总ABTS百分比平均为64.8%。【结论】稻壳中含有较丰富的酚类物质，具有较强的抗氧化活性。稻壳总酚、总黄酮含量、单体酚组成及其抗氧化活性均以结合态形式为主，且有显著的品种间差异。提示水稻谷壳可以作为一种潜在的天然抗氧化剂资源进行开发利用。

Free and Bound Phenolic Contents and Antioxidant Activity of Five Varieties of Indica Rice Husk

【Objective】 The contents and compositions of free and bound phenolics and antioxidant activity of husks of different rice varieties were compared. 【Method】 The contents of free and bound phenolics and flavonoids of rice husks of five different varieties were determined. High performance liquid chromatography (HPLC) method was used to measure the compositions and contents of phenolics in rice husks. The antioxidant activity was analyzed using the ferric reducing ability of plasma (FRAP) and ABTS radical cation scavenging activity assays. 【Result】 The free , bound and total phenolic contents of the husks of 5 tested indica rice varieties ranged from 42.8 to 123.0, 260.9 to 325.2 and 320.2 to 398.3 mg of gallic acid equivalents/100 g dry weight (DW), respectively. The average percentage contribution of bound phenolics to the total was 78.9%. The free, bound and total flavonoids contents of the husks ranged from 34.0 to 58.0, 47.9 to 64.4 and 82.0 to 115.7 mg of catechin equivalents/100 g DW, respectively. The average percentage contribution of bound flavonoids to the total was 56.4%. Gallic acid, protocatechuic acid, chlorogenic acid, vanillic acid, caffeic acid, syringic acid, p-coumaric acid and ferulic acid were detected in phenolic extracts of rice husks. Syringic acid and p-coumaric acid were the major free phenolics, with average of 25.09 μg?g-1 DW and 31.21 μg?g-1 DW, respectively. The most abundant bound phenolics was p-coumaric acid, and its average content was 2141.61 μg?g-1 DW. The free , bound and total FRAP antioxidant activity of the husks ranged from 37.7 to 106.0, 217.9 to 281.0, and 269.3 to 370.3 mg Trolox equivalents/100 g DW. The average percentage contribution of bound FRAP antioxidant activity to the total was 77.3%. The free , bound and total ABTS antioxidant activities of the husks ranged from 26.3 to 85.8, 67.2 to 111.9, and 93.4 to155.2 mg Trolox equivalents/100 g DW. The average percentage contribution of bound ABTS antioxidant activity to the total was 64.8%.【Conclusion】 Rice husk is rich in phenolics and possesses high antioxidant activity. Total phenolics and flavonoids, individual phenolics and antioxidant activity of 5 the tested rice husks were mainly contributed in bound form. Significant varietal differences were found. It is indicated that rice husk can be considered as a potential valuable source of the natural antioxidants.