Dong Yaoyao, Shi Shaoxia, Li Qi, Zhang Lingyan, Yu Xiuzhu
College of Food Science and Engineering, Northwest A&F University 22 Xinong Road Yangling 712100 Shaanxi P. R. China
RSC Adv. 2020 Jun 24;10(40):24073-24078. doi: 10.1039/d0ra03668d. eCollection 2020 Jun 19.
In this study, we developed a novel approach for determining a free fatty acid (FFA) in vegetable oils using attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy. FFA was converted to carboxylate species by a reaction with phthalimide potassium salt, and the linear relationship between FFA content and ATR-FTIR peak areas at 1541-1616 cm (1595 cm as baseline) was established. Results showed that the values obtained during calibration and validation were more than 0.99. The calibration method concurred to within ±0.035% over the range of 0.4% to 4.0% (quantitative determination of the percentage of FFA in oils, expressed as the percentage of oleic acid). In the calibration model, the root mean square error of prediction was 0.0104, the relative error was less than 0.246% and the relative average deviation was 0.386%, respectively. These indexes demonstrated that the calibration model has great accuracy, high precision and good stability. The indirect method established using ATR-FTIR has the advantages of excellent reproducibility, high exactitude, independent of oil type, simple operation and easy cleaning of the instrument surface. The slope of the verification equation between FFA prediction values and American Oil Chemists' Society's (AOCS) titration method was close to 1, value was more than 0.99. These indicators suggested that the proposed method and the AOCS method have a good correlation through AOCS titration and ATR-FTIR spectroscopy to determine validation samples parallel. In addition, for comparison, when the AOCS titration and ATR-FTIR spectroscopy methods were used for sample validation, the results indicated that the latter method is more reproducible, highly sensitive and has strong anti-disturbance. Therefore, the ATR-FTIR technique can be applied as a simple, highly sensitive, convenient and timely method for the analysis of FFAs in oils.
在本研究中，我们开发了一种使用衰减全反射傅里叶变换红外（ATR-FTIR）光谱法测定植物油中游离脂肪酸（FFA）的新方法。通过与邻苯二甲酰亚胺钾盐反应将FFA转化为羧酸盐物种，并建立了FFA含量与1541-1616 cm（以1595 cm为基线）处的ATR-FTIR峰面积之间的线性关系。结果表明，在校准和验证过程中获得的值均大于0.99。校准方法在0.4%至4.0%的范围内（以油酸百分比表示油中FFA百分比的定量测定）的误差在±0.035%以内。在校准模型中，预测的均方根误差为0.0104，相对误差小于0.246%，相对平均偏差为0.386%。这些指标表明校准模型具有很高的准确性、高精度和良好的稳定性。使用ATR-FTIR建立的间接方法具有重现性好、准确度高、不受油类型影响、操作简单且仪器表面易于清洁等优点。FFA预测值与美国油脂化学家协会（AOCS）滴定法之间验证方程的斜率接近1， 值大于0.99。这些指标表明，通过AOCS滴定和ATR-FTIR光谱法平行测定验证样品，所提出的方法与AOCS方法具有良好的相关性。此外，为了进行比较，当使用AOCS滴定法和ATR-FTIR光谱法进行样品验证时，结果表明后一种方法具有更高的重现性、高灵敏度和强抗干扰性。因此，ATR-FTIR技术可作为一种简单、高灵敏度、方便且及时的油中FFA分析方法。
