长期冰冻贮藏对龙眼肉多酚含量及抗氧化活性的影响

Effects of Long‐Term Frozen Storage on Polyphenol Content and Antioxidant Activity of Longan Pulp

以广西产22个品种龙眼肉为研究对象,采用福林酚法测定不同品种龙眼肉的多酚含量,利用1,1‐二苯基‐2‐三硝基苯肼(1,1‐diphenyl‐2‐picrylhydrazyl,DPPH)自由基清除能力、2,2′‐联氮‐双‐3‐乙基苯并噻唑啉‐6‐磺酸[2,2′‐azinobis(3‐ethylbenzothiazoline‐6‐sulfonic acid),ABTS]阳离子自由基清除能力、铁离子还原能力法测定其抗氧化活性,并研究长期冰冻贮藏前后多酚含量和抗氧化活性的变化。研究结果表明,不同品种龙眼肉之间多酚含量差异明显,鲜品中大乌圆多酚含量最高,畹町多酚含量最低,分别为84.83、6.74 mg/g,两者之比为12.59。冰冻贮藏5个月后,冻品中多酚含量最高和最低的品种分别为龙优和西贡1号。对比研究长期冷冻贮藏前后多酚含量变化发现,灵龙和畹町冷冻前后多酚含量基本不变,均在7 mg/g左右,其余品种均明显下降。其中下降最明显的前3个品种为大乌圆、早熟广眼和泰国热带,分别下降92.17%、91.87%和90.38%。与鲜品早熟广眼、青皮石硖相比,鲜品大乌圆具有更好的抗氧化活性。长期冰冻条件下,龙眼肉对ABTS+自由基清除能力和对铁离子还原能力均下降,对DPPH自由基清除能力增加。综上,龙眼肉鲜品多酚含量高、抗氧化能力强。

The polyphenol content in the pulp of 22 longan varieties in Guangxi was determined by the Folin‐Ciocalteu method.The antioxidant activity of the pulp was evaluated based on the DPPH and ABTS+free radical scavenging activities and the ferric reducing antioxidant power(FRAP).The variations in polyphenol content and antioxidant activity after long‐term frozen storage were studied.The results showed that there were significant differences in polyphenol content in the pulp among different varieties of longan.Among these varieties,the fresh pulp of′Dawuyuan′had highest polyphenol content of 84.83 mg/g,which was 12.59 folds of that(6.74 mg/g)in fresh pulp of′Wanding′with the lowest polyphenol content.After storage at-20℃for 5 months,′Longyou′and′Xigong NO.1′possessed the highest and lowest polyphenol content,respectively.The polyphenol content of′Linglong′and′Wanding′was around 7 mg/g before and after long‐term frozen storage,while that of other varieties decreased significantly.′Dawuyuan′,′Zaoshuguangyan′,and′Thailand tropical′were the three varieties with the largest decreases(92.17%,91.87%,and 90.38%,respectively).The fresh pulp of′Dawuyuan′possessed higher antioxidant activity than that of′Zaoshuguangyan′and′Qingpishixia′.After long‐term frozen storage,longan pulp showed decreased ABTS+free radical scavenging activity and FRAP and increased DPPH free radical scavenging activity.In summary,the fresh pulp of longan had high polyphenol content and strong antioxidant activity.