食用油掺假侵害消费者权益, 危害公众健康, 相关鉴别研究具有重要意义。 当掺假食用油中的假冒组分含量降低时, 掺假油与正品油的相似度较高, 通常难以精准鉴别。 因此, 低量掺假食用油是打假鉴别的难点和重点。 选取降温作为扰动因子, 采用同步二维拉曼相关谱, 结合系统聚类分析, 针对橄榄油低量掺假(5%, 10%, 20%)开展鉴别研究。 选取与橄榄油相似度很高的大豆油作为假冒组分。 结果显示, 在+15~0 ℃范围, 纯橄榄油与掺假橄榄油的拉曼光谱近乎相同, 谱图随温度变化不明显; 在2 850, 2 874, 2 906, 2 933, 2 958和3 005 cm^-1附近出现特征峰; 2 850 cm^-1处的特征峰对应于亚甲基(CH₂)的对称伸缩振动, 相对峰强最大。 当温度降至0 ℃以下时(-5~-20 ℃), 纯橄榄油和掺假橄榄油的拉曼光谱, 均随温度降低发生较显著变化; 相应地, 拉曼光谱差异随之增大。 主要特征峰位于2 848, 2 883, 2 933, 2 956和3 005 cm^-1附近。 在2 848 cm^-1处的特征峰为亚甲基对称伸缩振动的特征峰(2 850 cm^-1)随温度降低发生红移所致, 其相对峰强随温度降低呈现减弱趋势。 在2 883 cm^-1处的特征峰对应于CH₂的反对称伸缩振动, 其相对强度随温度降低逐渐增大, 成为最强特征峰。 同步二维拉曼相关谱显示, 纯橄榄油在2 925 cm^-1的自相关峰强度最大, 此自相关峰的强度排序为: 纯橄榄>掺假5%橄榄油>掺假10%橄榄油>掺假20%橄榄油。 纯橄榄油在2 925和2 883 cm^-1处的负交叉峰强度最大, 此负交叉峰强度排序为: 纯橄榄>掺假5%橄榄油>掺假10%橄榄油>掺假20%橄榄油。 对同步二维拉曼相关谱的系统聚类分析显示, 纯橄榄油和低量掺假橄榄油的盲样均得到准确鉴别。 采用降温作为扰动因子的同步二维拉曼相关谱具有很高的辨识力, 对橄榄油中掺杂地沟油等其他假冒组分, 以及其他油品的防伪鉴别也具有理论和实用价值。

The doping of inferior or low-priced oils into the edible oil infringes consumers’ rights and harms public health. Therefore, the anti-counterfeiting identification of edible oils is of great significance. When the content of counterfeit components in the adulterated oil decreases, the similarity between the genuine oil and the adulterated oil becomes higher so that the identification of low-doping oil is generally difficult. In this paper, synchronous two-dimensional Raman correlation spectroscopy with cooling as a perturbation factor was used for the identification of the pure and the low-doping (5%, 10%, 20%) olive oils. Soybean oil with high similarity to the olive oil was selected as a counterfeit component. In the range of 15 to 0 centigrade degree, the Raman spectra of the pure and the adulterated olive oils were similar and changed slightly when the temperature decreased. The characteristic peaks appeared at 2 850, 2 874, 2 906, 2 933, 2 958, 3 005 cm^-1. The characteristic peak at 2 850 cm^-1 corresponding to the symmetric stretching vibration of methylene (CH₂) was the strongest peak. When the temperature dropped below 0 centigrade degree, the Raman spectra of the pure and the adulterated olive oils changed significantly along with the decrease of temperature. In the range of -5 to -20 centigrade degree, the characteristic peaks appeared around 2 848, 2 883, 2 933, 2 956, 3 005 cm^-1. The peak at 2 848 cm^-1 was attributed to the redshift of the peak (2 850 cm^-1) of the symmetric stretching vibration of CH₂, and its relative peak strength decreased with the dropping of temperature; meanwhile, the peak at 2 883 cm^-1 corresponding to the asymmetrical stretching vibration of CH₂ gradually increased and became the strongest peak. Synchronous two-dimensional Raman correlation spectra showed that the strength of the auto peak around 2 925 cm^-1 and that of the negative cross peak at (2 925, 2 883 cm^-1) remarkably decreased with the increase of doping ratio, and the two-dimensional spectral difference among the pure and the low-doping (5%, 10%, 20%) olive oils was significant. Hierarchical clustering analysis based on the synchronous two-dimensional Raman correlation spectra showed that the blind samples of the pure and the low-doping olive oils were all accurately identified. Synchronous two-dimensional Raman correlation spectroscopy with cooling as a perturbation factor is efficient to distinguish the low-doping oils from the genuine olive oil and can be also helpful for the identification of other kinds of oils.