Adom Kafui Kwami, Liu Rui Hai
Department of Food Science, Cornell University, Stocking Hall, Ithaca, New York 14853-7201, USA.
J Agric Food Chem. 2002 Oct 9;50(21):6182-7. doi: 10.1021/jf0205099.
Epidemiological studies have shown that consumption of whole grains and grain-based products is associated with reduced risk of chronic diseases. The health benefits of whole grains are attributed in part to their unique phytochemical composition. However, the phytochemical contents in grains have been commonly underestimated in the literature, because bound phytochemicals were not included. This study was designed to investigate the complete phytochemical profiles in free, soluble conjugated, and insoluble bound forms, as well as their antioxidant activities in uncooked whole grains. Corn had the highest total phenolic content (15.55 +/- 0.60 micromol of gallic acid equiv/g of grain) of the grains tested, followed by wheat (7.99 +/- 0.39 micromol of gallic acid equiv/g of grain), oats (6.53 +/- 0.19 micromol of gallic acid equiv/g of grain), and rice (5.56 +/- 0.17 micromol of gallic acid equiv/g of grain). The major portion of phenolics in grains existed in the bound form (85% in corn, 75% in oats and wheat, and 62% in rice), although free phenolics were frequently reported in the literature. Ferulic acid was the major phenolic compound in grains tested, with free, soluble-conjugated, and bound ferulic acids present in the ratio 0.1:1:100. Corn had the highest total antioxidant activity (181.42 +/- 0.86 micromol of vitamin C equiv/g of grain), followed by wheat (76.70 +/- 1.38 micromol of vitamin C equiv/g of grain), oats (74.67 +/- 1.49 micromol of vitamin C equiv/g of grain), and rice (55.77 +/- 1.62 micromol of vitamin C equiv/g of grain). Bound phytochemicals were the major contributors to the total antioxidant activity: 90% in wheat, 87% in corn, 71% in rice, and 58% in oats. Bound phytochemicals could survive stomach and intestinal digestion to reach the colon. This may partly explain the mechanism of grain consumption in the prevention of colon cancer, other digestive cancers, breast cancer, and prostate cancer, which is supported by epidemiological studies.
流行病学研究表明，食用全谷物和谷物类产品与降低慢性病风险有关。全谷物的健康益处部分归因于其独特的植物化学成分。然而，谷物中的植物化学成分在文献中通常被低估，因为未包括结合态的植物化学成分。本研究旨在调查生全谷物中游离态、可溶性共轭态和不溶性结合态的完整植物化学概况，以及它们的抗氧化活性。在所测试的谷物中，玉米的总酚含量最高（15.55±0.60微摩尔没食子酸当量/克谷物），其次是小麦（7.99±0.39微摩尔没食子酸当量/克谷物）、燕麦（6.53±0.19微摩尔没食子酸当量/克谷物）和大米（5.56±0.17微摩尔没食子酸当量/克谷物）。谷物中酚类物质的主要部分以结合态存在（玉米中占85%，燕麦和小麦中占75%，大米中占62%），尽管文献中经常报道游离酚类物质。阿魏酸是所测试谷物中的主要酚类化合物，游离态、可溶性共轭态和结合态阿魏酸的比例为0.1:1:100。玉米的总抗氧化活性最高（181.42±0.86微摩尔维生素C当量/克谷物），其次是小麦（76.70±1.38微摩尔维生素C当量/克谷物）、燕麦（74.67±1.49微摩尔维生素C当量/克谷物）和大米（55.77±1.62微摩尔维生素C当量/克谷物）。结合态植物化学成分是总抗氧化活性的主要贡献者：小麦中占90%，玉米中占87%，大米中占71%，燕麦中占58%。结合态植物化学成分能够在胃和肠道消化过程中存活下来并到达结肠。这可能部分解释了食用谷物预防结肠癌、其他消化系统癌症、乳腺癌和前列腺癌的机制，这得到了流行病学研究的支持。
