Lotito Silvina B, Frei Balz
Linus Pauling Institute, Oregon State University, Corvallis, OR 97331, USA.
Free Radic Biol Med. 2004 Jan 15;36(2):201-11. doi: 10.1016/j.freeradbiomed.2003.10.005.
Apples are a major source of flavonoids in the Western diet, and flavonoid-rich foods may help protect against chronic diseases by antioxidant mechanisms. In the present study we investigated: (1) the antioxidant capacity of representative apple polyphenols and their contribution to the total antioxidant capacity of apple extracts; (2) the effects of adding apple extract to human plasma in vitro on oxidation of endogenous antioxidants and lipids; and (3) the effects of apple consumption by humans on ex vivo oxidation of plasma antioxidants and lipids. We found that the apple-contained flavonols and flavanols, quercetin, rutin, (-)-epicatechin, and (+)-catechin, had a higher antioxidant capacity than the dihydrochalcones, phloridzin and phloretin, and the hydroxycinnamate, chlorogenic acid. However, together these apple polyphenols contributed less than 20% to the total antioxidant capacity of aqueous apple extracts. When human plasma was exposed to a constant flux of aqueous peroxyl radicals, endogenous ascorbate (70.0 +/- 10.3 microM) was oxidized within 45 min of incubation, while endogenous urate (375 +/- 40 microM) and alpha-tocopherol (24.7 +/- 1.2 microM) were oxidized after ascorbate. Addition of 7.1 or 14.3 micrograms/ml total phenols of apple extract did not protect ascorbate from oxidation, but increased the half-life (t1/2) of urate from 136 +/- 15 to 192 +/- 16 and 208 +/- 23 min, respectively (p < 0.05 each), and t1/2 of alpha-tocopherol from 141 +/- 18 to 164 +/- 8 min (p = ns) and 188 +/- 8 min (p < 0.05). Lipid peroxidation started after ascorbate depletion, and addition of apple extract increased the lag time preceding detectable lipid peroxidation from 36.3 +/- 3.7 to 50.9 +/- 2.7 min (p < 0.05) and 70.4 +/- 4.2 min (p < 0.001). However, when six healthy volunteers ate five apples and plasma was obtained up to 4 h after apple consumption, no significant increases in the resistance to oxidation of endogenous urate, alpha-tocopherol, and lipids were found. Thus, despite the high antioxidant capacity of individual apple polyphenols and apple extracts and the significant antioxidant effects of apple extract added to human plasma in vitro, ingestion of large amounts of apples by humans does not appear to result in equivalent in vivo antioxidant effects of apple polyphenols.
在西方饮食中，苹果是黄酮类化合物的主要来源，富含黄酮类化合物的食物可能通过抗氧化机制帮助预防慢性疾病。在本研究中，我们调查了：（1）代表性苹果多酚的抗氧化能力及其对苹果提取物总抗氧化能力的贡献；（2）体外向人血浆中添加苹果提取物对内源性抗氧化剂和脂质氧化的影响；（3）人类食用苹果对血浆抗氧化剂和脂质体外氧化的影响。我们发现，苹果中含有的黄酮醇和黄烷醇、槲皮素、芦丁、（-）-表儿茶素和（+）-儿茶素的抗氧化能力高于二氢查耳酮、根皮苷和根皮素以及羟基肉桂酸、绿原酸。然而，这些苹果多酚加起来对苹果水提取物的总抗氧化能力的贡献不到20%。当人血浆暴露于恒定通量的过氧自由基水溶液时，内源性抗坏血酸（70.0±10.3微摩尔）在孵育45分钟内被氧化，而内源性尿酸盐（375±40微摩尔）和α-生育酚（24.7±1.2微摩尔）在抗坏血酸之后被氧化。添加7.1或14.3微克/毫升总酚的苹果提取物不能保护抗坏血酸不被氧化，但分别将尿酸盐的半衰期（t1/2）从136±15分钟增加到192±16分钟和208±23分钟（各p<0.05），将α-生育酚的t1/2从141±18分钟增加到164±8分钟（p=无显著性差异）和188±8分钟（p<0.05）。脂质过氧化在抗坏血酸耗尽后开始，添加苹果提取物使可检测到的脂质过氧化之前的延迟时间从36.3±3.7分钟增加到50.9±2.7分钟（p<0.05）和70.4±4.2分钟（p<0.001）。然而，当六名健康志愿者吃了五个苹果并在食用苹果后长达4小时采集血浆时，未发现内源性尿酸盐、α-生育酚和脂质抗氧化能力有显著增加。因此，尽管单个苹果多酚和苹果提取物具有高抗氧化能力，且体外向人血浆中添加苹果提取物具有显著抗氧化作用，但人类大量食用苹果似乎不会产生苹果多酚在体内的等效抗氧化效果。
