A new evaluation method for anti-oxidant activity based on structure change of protein caused by radicals

本研究提出了一种评价食品中水溶性成分抗氧化活性的简便方法。通过比较409 nm处肌红蛋白（标准参比）吸光度的变化，研究了抗氧化剂对次氯酸盐离子或羟基自由基的保护作用。保护比是通过添加或不添加抗氧化剂时肌红蛋白的吸光度变化来定义的，它是定量评价抗次氯酸根或羟基自由基活性的一个很好的指标。雷达图显示了对DPPH （1,1 -cliphenyl-2- picrylhyadyl）、次氯酸盐离子和羟基自由基的抗氧化活性，清楚地区分了五种抗氧化剂的特征，包括肌肽、谷胱甘肽和维生素c。为了证明所提出方法的有效性，我们对三种多酚化合物、茶（绿茶、乌龙茶和红茶）和五种市售瓶装茶的抗氧化活性进行了评估。之所以选择茶叶作为例子，是因为尽管消费者对茶叶的抗氧化活性非常关注，但尚未建立全面的抗氧化性能评价方法。所有多酚化合物对这三种自由基均表现出较高的活性。在雷达图上，所有茶叶都显示出与多酚化合物相似的模式。然而，活性的强度很大程度上取决于样品。利用雷达图对不同茶叶的抗氧化活性进行了综合评价。该方法可用于评价和表征各种食品中水溶性抗氧化剂的活性。

A simple method to evaluate antioxidant activities of water-soluble ingredients of foods has been developed in this research project. Protective effects of antioxidants against hypochlorite ion or hydroxyl radical have been studied by comparing changes in absorbance of myoglobin (a standard reference) at 409 nm. Protective ratio, defined by absorbance changes of myoglobin with or without the antioxidant, was a good indicator to quantitatively evaluate the antioxidant activity against the hypochlorite radical or the hydroxyl radical, respectively. Radar charts indicating the antioxidant activities against DPPH (1, 1-cliphenyl-2-picrylhydradyl), hypochlorite ion, and hydroxyl radical clearly differentiated the characteristics of five antioxidants including carnosine, glutathione, and vitamin C.In order to demonstrate the effectiveness of the proposed method, antioxidant activities of three polyphenol compounds, teas (green tea, oolong tea, and black tea), and five commercially available bottled teas have been evaluated. Teas were chosen as examples because comprehensive methods to evaluate antioxidant properties have not been established yet in spite of consumers' strong concern fir the antioxidant activities of teas. All polyphenol compounds showed relatively high activities against all three radicals. All teas showed similar patterns as the polyphenol compounds in the radar charts. The strength of the activities, however, strongly depends on the samples. Thus, the antioxidant activities of various teas have been successfully evaluated in a comprehensive way using the radar charts. The simple method proposed in this rematch project would be useful to evaluate and characterize the activities of water-soluble antioxidants contained in various food materials.