Ministry of Food, Agriculture and Livestock, Ankara, Turkey.
Food Engineering Department, Hacettepe University, Beytepe, Ankara, Turkey.
Food Chem. 2016 Jan 1;190:25-32. doi: 10.1016/j.foodchem.2015.05.069. Epub 2015 May 16.
Influence of pH on the antioxidant activities of combinations of lettuce extract (LE) with quercetin (QC), green tea extract (GTE) or grape seed extract (GSE) was investigated for both reduction of Fremy's salt in aqueous solution using direct electron spin resonance (ESR) spectroscopy and in L-α-phosphatidylcholine liposome peroxidation assay measured following formation of conjugated dienes. All examined phenolic antioxidants showed increasing radical scavenging effect with increasing pH values by using both methods. QC, GTE and GSE acted synergistically in combination with LE against oxidation of peroxidating liposomes and with QC showing the largest effect. The pH dependent increase of the antioxidant activity of the phenols is due to an increase of their electron-donating ability upon deprotonation and to their stabilization in alkaline solutions leading to polymerization reaction. Such polymerization reactions of polyphenolic antioxidants can form new oxidizable -OH moieties in their polymeric products resulting in a higher radical scavenging activity.
采用直接电子自旋共振（ESR）光谱法测定弗来米盐在水溶液中的还原情况和测定形成共轭二烯后 L-α-磷脂酰胆碱脂体过氧化的方法，研究了在不同 pH 值条件下生菜提取物（LE）分别与槲皮素（QC）、绿茶提取物（GTE）和葡萄籽提取物（GSE）组合时的抗氧化活性。通过这两种方法，所有被检测的酚类抗氧化剂的自由基清除效果都随着 pH 值的增加而增强。QC、GTE 和 GSE 与 LE 联合作用可增强脂体过氧化的抗氧化能力，其中 QC 的效果最大。酚类抗氧化剂的抗氧化活性随 pH 值升高而增加是由于去质子化增加了其供电子能力，并且在碱性溶液中稳定化导致聚合反应。多酚类抗氧化剂的这种聚合反应可以在其聚合产物中形成新的可氧化的-OH 部分，从而具有更高的自由基清除活性。
