| Edible oils are highly susceptible to oxidization and decomposition because of inappropriate temperature,light and oxygen during processing and storage.In addition,the initial oxidation products that accumulate in oils are hydro-peroxides,which may subsequently break down to form lower-molecular weight compounds,such as alcohols,aldehydes,free fatty acids,and ketones.These compounds for long-term intake have damage in health.Therefore,the detecting technique for oxidation process of oils and fats,especially the peroxide value(PV)is particularly significant.The detecting techniques of Fourier infrared spectrum(FTIR)can provide the information on groups of C、H、O,which is very suitable for monitoring of edible oil oxidation process.However,the traditional methods for oil oxidation detection based on FTIR technique involve complicated procedures,large amounts of organic solvent and time-consuming,which is not conducive to promote in the actual application.In this research,we develop a novel and reliable detection method based on FTIR technology,using the low cost of polyethylene(PE)film for sample testing carrier,which are not only simplify the testing process and reduce the cost,but also overcome the low accuracy and high error of the traditional test method.Taken the common edible oils in our country as raw material,we study the changing process of PV in oxidation using the novel polyethylene film-Fourier infrared spectrum(PE-FTIR)detection technology from such four aspects as correction to optical path of edible oil films,qualitative analysis of PV,real-time monitoring of oxidation process and quantitative analysis of PV.A series of mathematical analysis models with high credibility and good predictive ability have been established by this method.Fast and efficient real-time detection of PV can be carried out with low test cost.The main contents and results are as follows:(1)Based on the absorption band of triphenylphosphine oxide(TPPO)at 542 cm-1 in FITR spectrum change with the concentration of TPPO,a series of linear calibration equations relating among concentration of TPPO,optical path of edible oil films and intensity of the absorption band of edible oil in FTIR spectrum are obtained by the two-dimensional correlation spectroscopy technique.Then,a calibration model between the intensity changes of absorption band and those of optical path is established,which could normalize the spectrum for qualitative and quantitative analysis.In addition,the use of PE or mesh film for oil testing carrier could simplify the preparation process of oils samples by FTIR.On that basis,we develop the novel FTIR detection technology.(2)Taken the common edible oils as raw material,PVs of oils were measured according to the national standard(GB/T 5538-5538/ISO 3960:2001)and then established a reference set.The qualitative analysis of edible oils with different oxidation degrees are performed with the application of FTIR technology to adjust the optical path and combining with the markov distance discriminanting analysis method.The results of model validation show that the recognition rate of the established discriminant model can reach to 100%at the wave-number range of 3750-3150 cm-1 with the application of PE-FTIR technology combined with markov distance discriminant analysis.(3)Chosen soybean oil,peanut oil,flax seed oil and palm oil as testing material,we studied the growth of PV with the change of storage time in a simulated storage situation by the adhibition of FTIR technology,employed the characteristic absorption band(3444/3295 cm-1)intensity of edible oils as the criterion for oil oxidation process and screen mesh as testing carrier.Tests results reveal that screen mesh can also be appropriate for testing carrier in FTIR detection technology while applying in the real-time monitoring process of oil oxidation at high temperature.(4)Basing on the stoichiometric reaction of hydroperoxides with the triphenylphosphine(TPP)in oil to produce TPPO and the absorption band of TPPO at 542 cm-1 in FITR spectrum change with the concentration of TPPO,a novel FTIR quantitative analysis method of edible oil’s PV has been established with application of PE-FTIR technology.To test validation set samples using this analysis method.The results can be predicted by the following equation:y=0.1524+172.75x;SD = 0.1335,the PV determinations are made on two sets of validation samples,spanning PV ranges of 0-25 and 0-2 mmol/kg in oil,and carried out in parallel using the AOCS titrimetric and PE-based FTIR procedures.Comparison of the results of the duplicate analyses of these two methods indicates that the latter was more reproducible and slightly more sensitive. |
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