基于电子自旋共振和拉曼光谱技术的榛子油氧化特性探析与评价

Analysis and Evaluation on Oxidation Characteristics of Hazelnut Oil Based on Electron Spin Resonance and Raman Spectroscopy

【目的】研究榛子油氧化过程中的品质变化规律、自由基产生规律以及油脂内部分子结构的变化,揭示榛子油氧化特性,为榛子油品质检测与货架期预测提供重要的理论依据和技术支持。【方法】以平欧杂种榛主栽品种‘达维’为试验材料,采用60℃烘箱法进行榛子油加速氧化试验,测定榛子油在氧化过程中过氧化值(POV)、p-茴香胺值(AV)、总氧化值(TV)、共轭二烯值、脂肪酸相对含量、总类胡萝卜素含量、自由基相对含量和分子内部结构的变化规律,并对各指标进行相关性分析。【结果】榛子油氧化过程中,POV、AV、TV和共轭二烯值的初始值分别为6.22 meq·kg-1、0.31、12.75和0.12,加速氧化40天后分别显著增加至370.47 meq·kg-1、25.91、766.85和3.48,饱和脂肪酸、不饱和脂肪酸相对含量分别从5.96%、93.69%变化至6.35%、93.20%,自由基相对含量从8.41快速增加至28.09;榛子油中总类胡萝卜素氧化30天时含量为0;拉曼光谱中类胡萝素1158和1524 cm-1特征峰强度变化与总类胡萝卜素含量的变化趋势保持一致;拉曼相对强度I972 cm-1/I1441 cm-1、I1268 cm-1/I1441 cm-1、I1158 cm-1/I1441 cm-1和I1524 cm-1/I1441 cm-1均与不饱和度呈正相关。【结论】榛子油氧化大致分为3个阶段,即初始缓慢氧化阶段、中间快速氧化阶段和后期深度氧化阶段,综合4个常规氧化指标(POV、AV、TV和共轭二烯值)可以很好评价榛子油的氧化程度;类胡萝卜素是榛子油色泽的主要贡献因子,与榛子油氧化程度密切相关;自由基相对含量、拉曼光谱特征峰强度和总类胡萝卜素含量指标与常规氧化指标具有极显著相关性,证明电子自旋共振和拉曼光谱技术可用于评价榛子油的氧化程度;电子自旋共振和拉曼光谱技术作为传统油质氧化评价方法的补充或替代具有很大潜力,可为油脂品质快速检测提供新方法。

【Objective】This study investigated the quality change,free radical formation and fatty acid composition of hazelnut oil during oxidation process,and there by revealed the oxidative characteristics which aimed to provide important theoretical basis and technical supports for the quality detection and shelf life prediction for hazelnut oil.【Method】A main cultivar of hybrid hazelnut(Corylus heterophylla×C.avellana‘Dawei’)was used as the trial material.Hazelnut oil was obtained by the screw pressing method.The accelerated oxidation experiment of hazelnut oil was carried out in an oven at 60℃.The changed regulation of peroxide value(POV),p-anisidine value(AV),total oxidation value(TV),conjugated diene value,relative contents of fatty acids,total carotenoid content,relative content of free radicals and internal structure of the molecules were determined in hazelnut oil during the oxidative period,and the correlations of these indicators were analyzed.【Result】During the oxidative process of hazelnut oil,the initial values of POV,AV,TV and conjugated diene were 6.22 meq·kg-1,0.31,12.75 and 0.12,and then the values increased significantly to 370.47 meq·kg-1,25.91,766.85 and 3.48 at the end of the oxidation process for 40 days,respectively.The relative contents of saturated fatty acids and unsaturated fatty acids changed from 5.96%and 93.69%to 6.35%and 93.20%,respectively.The relative content of free radicals increased rapidly from 8.41 to 28.09.Total carotenoid content of hazelnut oil was not detected after 30 days of oxidation.The change of characteristic peak intensity of 1158 cm-1 and 1524 cm-1 in Raman spectra was consistent with total carotenoid content.Raman relative intensities of I972 cm-1/I1441 cm-1,I1268 cm-1/I1441 cm-1,I1158 cm-1/I1441 cm-1 and I1524 cm-1/I1441 cm-1 were positively correlated with the unsaturated degree.【Conclusion】The oxidation of hazelnut oil is roughly divided into three stages,namely initial slowly oxidative stage,rapidly intermediate oxidative stage and later deeply oxidative stage.The oxidative degree of hazelnut oil can be well evaluated according to comprehensive four oxidation indexes(namely,POV,AV,TV and conjugated diene value).Carotenoids are the main contribution factors to the color of hazelnut oil,and closely related to the oxidative degree of hazelnut oil.The relative content of free radicals,characteristic peak intensity of Raman spectra and total carotenoid content have a significant correlation with conventional oxidation indexes,which proves that electron spin resonance(ESR)and Raman spectroscopy can be used to evaluate the oxidative degree in hazelnut oil.ESR and Raman spectroscopy have great potential as supplement or replacement for evaluation methods of traditional lipid oxidation,providing a new method for rapidly nondestructive test of lipid quality.