荔枝多酚的抗氧化性动力学及稳定性

Antioxidant Activity and Stability of Litchi Polyphenols

采用DPPH自由基清除法和铁还原比色法研究荔枝多酚的抗氧化性。水相/有机相荔枝多酚的DPPH自由基清除能力及铁离子还原能力的动力学反应模式均表现为剂量及反应时间的双重依赖关系。荔枝多酚对温度敏感。随着温度的升高(25～70℃),其多酚含量及其抗氧化活性均呈下降趋势;荔枝多酚含量及抗氧化性在弱碱性范围内(pH8～9)较稳定;荔枝多酚对光照敏感,随着光照时间的延长(12～96h),其多酚含量及其抗氧化活性逐渐下降;荔枝多酚含量与其抗氧化活性相关性较强,当处理造成荔枝多酚含量发生改变时,其抗氧化活性也发生较大变化。低温、弱碱性及避光均有利于荔枝多酚含量与其抗氧化活性的稳定。

In this study,fresh litchi pulp was extracted with 70% aqueous ethanol twice by shaking for 6 h each time;afterward,the resulting extracts were pooled,condensed by rotary evaporation,defatted with n-hexane and reextracted with ethyl acetate/ethyl ether mixture（1：1,V/V）;and finally,an organic phase and an aqueous phase both containing polyphenols were obtained.The antioxidant activity of litchi polyphenols in the two phases was evaluated by DPPH radical scavenging and ferric reducing antioxidant power（FRAP） assays.Meanwhile,the relationship between total phenol content（TPC） and antioxidant activity of the two phases were explored.The stability and antioxidant activity of litchi polyphenols showed a downward trend with increasing temperature（25-70 ℃）,and prolonged exposure to sunlight（12-96 h） could also result in a gradual decrease in the stability and antioxidant activity of litchi polyphenols.TPC and antioxidant activities of both polyphenolic extracts were kept stable in the pH range of 8-9.Meanwhile,an obvious correlation between TPC and antioxidant activity was observed for both polyphenolic extracts（P0.05）.Therefore,lower temperature and light-free environments are benefit for TPC and antioxidant activity of litchi polyphenols during storage and processing.