The Study Of The Rapid Determination Of Physical-chemical Indexes In Edible Oils Based On FTIR Method

Oxidation,polymerization,pyrolysis and hydrolysis will occur in edible oils under storage and frying.These reaction will produce toxic substances,deteriorate the oil quality,rise the undesirable flavors and damage human health.According to these disadvantages,the quality control of oils while store and using is particularly important,and it is of great significance to determine the hygienic-quality index.Currently,the standard methods of these index are rather time-consuming,tedious and costing a large amount of organic reagent,so it is not adapted for real time analysis and large number of samples.Fourier transform infrared?FTIR?spectroscopy is accurate,rapid,non-destructive and environment friendly.So it is playing an important role in analysis of food and agricultural products.This research is based on FTIR method,combining with stoichiometric reaction and partial least squares?PLS?to establish a rapid determination of acid value?AV?,peroxide value?PV?and total polar compound?TPC?.First,using stoichiometric reaction between sodium phenate and free fatty acid in edible oils to produce the phenate absorption band at 1588 cm^-1 and carboxylate absorption band at 1569 cm^-1,respectively,in the second-derivative differential spectra.Both coefficient of the calibration is greater than 0.997,showed a good linear relationship.Theoretic precision was±0.1441 mg KOH/g and±0.0469%respectively.The FTIR acidity predictions were compared to the AOCS titrimetric method using real samples and frying samples,the overall error is less than 5%.The results showed that FTIR method is more accurate and reproducible in determining AV.The FTIR method overcomes a variety of limitations of earlier FTIR-based methods,being particularly simple and well suited to routine,semi-automated acidity analysis of edible oils using a basic FTIR spectrometer.Second,using p-Toluenesulfonyl isocyanate?p-TSI?to react with peroxide in edible oils,the measurement of absorption band at 2235 cm^-1was related to PV by titration method.The coefficient of the calibration is0.9995,and theoretic precision is±0.0042 g/100g,showed a good stability of calibration.The verification of the calibration shows that the FTIR method is accurate and more rapid as AOCS method.For different type of refined oil,the error was 2.36%,it is lower than it of fried oils.Although the overall error is 4.56%shows a good adaptability of both refined and fried oils,and suitable for PV determination of large amount of oil samples.Finally,based on the ATR-FTIR spectroscopy combined with the interval partial least squares?i-PLS?to determine the TPC of fried oils.Showed the great potential of this method to monitor the quality of fried oils.Collecting all spectrum of simulation samples as calibration set,and spectrum of fried oil from restaurants and food venders as validation set to build the model.After spectral preprocessing and interval selection,the optimization model was carry out by second derivative spectrum with interval of 3400-2800 cm^-1,1800-1400 cm^-1 and 1000-800 cm^-1.The R² of the model was 0.9929,RMSEC and RMSEP were 0.93 and 1.16,respectively.In the accuracy validation,the overall error of FTIR was 3.11%compared with AOCS method,shows a good accuracy,stability and good adaptability.In summary,this study is based on FTIR spectroscopy combined with stoichiometric reaction and partial least squares?PLS?to establish an accurate and rapid determination method to analyze the AV,PV and TPC of edible oils for both refined and fried oils.The study overcomes many disadvantages of tradition method,and shows a great potential to monitor these index.Offering a new way to control the oil quality by FTIR method.