羟基酪醇酶促聚合产物的表征及其抗氧化和热稳定性

Characterization, Antioxidant Activity and Thermostabiltiy of Hydroxytyrosol Polymerization Products Catalyzed by Laccase

利用漆酶对羟基酪醇(hydroxytyrosol,HT)进行酶促氧化聚合,运用紫外-可见分光光度计、傅里叶红外光谱、凝胶色谱和液相色谱-质谱联用对聚合产物进行表征。结果表明,形成的聚合物呈现多分散性(D=2.1),主要生成了三聚体、四聚体、六聚体化合物。同时,以VC和2,6-二叔丁基-4-甲基苯酚(dibutyl hydroxy toluene,BHT)为阳性对照,分别通过清除1,1-二苯基-2-三硝基苯肼自由基和热重-傅里叶变换红外光谱(thermogravimetry-Fourier transform infrared spectroscopy,TG-FTIR)联用的方法对其进行抗氧化性及热稳定性评价。结果表明,HT聚合物较HT和BHT具有更强的抗氧化性,分别约是其2.28倍和5.7倍,接近于VC(约是其72%)。基于热重微分曲线峰值温度(315.1℃)和残余质量所占百分比(66.09%)结果可知,HT聚合物的热稳定性较VC(228.1℃)、BHT(236.2℃)和HT(314.9℃)更强,且FTIR结果表明,HT聚合物及其他受试化合物均是以羟基断裂开始,脱氢形成醌式结构或脱水碳碳双键。这些数据可为HT的深加工利用提供理论和实践基础。

The oxidative polymerization of hydroxytyrosol was catalyzed by laccase.The resultant products were characterized by UV-Vis spectroscopy,FTIR spectroscopy,gel permeation chromatography(GPC)and high performance liquid chromatography-mass spectrometry(HPLC-MS).The results showed that the products were polydisperse(D=2.1),and mainly consisted of trimer,tetramer and hexamer.Meanwhile,the antioxidant activity and thermal stability of the polymers were assessed by 1,1-diphenyl-2-picrylhydrazyl(DPPH)radical scavenging assay and thermogravimetry-Fourier transform infrared spectroscopy(TG-FTIR)with VC and dibutyl hydroxy toluene(BHT)as positive control.The results indicated that the antioxidant activity of hydroxytyrosol polymers was 2.28 and 5.7 times as strong as HT and BHT,respectively and was similar to VC(72%as strong).On the basis of DTG peak temperature(315.1℃)and residual percentage(66.09%),the polymers had better thermal stability than VC(228.1℃),BHT(236.2℃)and HT(314.9℃).3D-FTIR spectra indicated that HT polymers together with the other tested compounds began with O–H bond breaking,forming a quinoid structure by dehydrogenation or carbon-carbon double bond by dehydration.All these findings will provide a good theoretical and practical foundation for deep hydroxytyrosol utilization.