Quality Change Of Animal Fats And Vegetable Oils In The Pan-frying Process And The Cytotoxicity Evaluation Of Their Sterol Oxides

With the accelerated pace of life and the rapid development of the food industry,the demand of consumers for fried foods grows continually.At the same time,the nutrition and safety of fried oils have also attracted consumers’attention.For a long time,people lack scientific understanding about quality change,service life and safety of fried foods during frying.In this research,there were two vegetable oils（e.g.,palm olein and corn oil）and two animal fats（e.g.,lard and basa fish oil）,which were pan-fried at 180°C for exploring the changes about the quality of the oils and functional components during frying.Phytosterol is one of functional constituents in oils,which will affect the quality and stability of frying oil,but its chemical detection is tedious and time-consuming.In this research,attenuated total reflection Fourier transform infrared spectroscopy（ATR-FTIR）combined with stoichiometry was used to establish to a way to detect total sterols efficiently and non-destructively.Some new ideas were provided for the rapid detection of sterols.Meanwhile,sterols are easily oxidized,then phytosterol oxides（POPs）and cholesterol oxides（COPs）may be produced in the pan-frying process,This will adversely affect the quality of frying oil and the health of consumers.At present,the biological effect of COPs has been extensively studied whereas that of POPs has been rarely reported.In this research,in vitro cell experiments were performed on both POPs and COP prepared by thermal oxidation in order to reveal the cytotoxicity effect of POPs.The main contents are as follows:（1）Chicken nuggets were used as the frying object,and palm olein,corn oil,lard and basa fish oil were used as the frying oils,which were pan-fried at 180°C for10 frying batches.The change of the physical and chemical indicators（e.g.,acid value,total oxidation value,total polar compounds and triglyceride polymer）,main components of oils（e.g.,glyceride composition and fatty acid composition）and functional components of oils（e.g.,total phenol,tocopherol,phytosterol and cholesterol）indicated the oil oxidation occurred during frying.After 10 batches of frying,the acid value remained below the national limit but the total oxidation value exceeded.The total polar compounds of all frying oils exceeded the national limit“27%”excepting basa fish oil.Results showed that palm olein,lard,and basa fish oil had similar fatty acid compositions,and the unsaturated fatty acid content of corn oil was too high to fry in a stable state.Moreover,the degradation of the polyunsaturated fatty acids in basa fish oil was slower than other three oils,thus basa fish oil could be considered as a new stable animal frying oil.Besides,the tocopherols decreased significantly during frying while no significant decreasing trend was found for the content of total phenols and sterols.（2）Sterols are common in animal and vegetable oils.because gas chromatography（GC）is tedious,time-consuming and detrimental to the sample,to quantitative the total sterol content in frying oils,a non-destructive and efficient detection method was established by ATR-FTIR combined with stoichiometry.Firstly,the real total sterol content in the frying oils were obtained by GC,which was analyzed with the combination of the ATR-FTIR spectrum.The entire spectrum(4000-600 cm^-1)of mid-infrared region and the characteristic spectrum of total sterol(1800-800 cm^-1)were used for the quantitative analysis.Secondly,a number of pre-processing steps were performed,including first derivative,second derivative,variable normalization and spectral normalization.Finally,a quantitative analysis model was constructed by cooperative partial least squares regression（Si PLS）.The obtained model was used to predict total sterol content,which had a high correlation with the real total sterol content.The root mean square error（RMSEP）and correlation coefficient（R_P）of sterols were respectively predicted as 977.4578 mg/kg and 0.9680,which proved the availability of ATR-FTIR spectroscopy combined with Si PLS for a fast and non-destructive analysis of total sterol content in frying oils.（3）Sterols may be oxidized to sterol oxides during frying,Using 7-keto beta-sitosterol oxide（7K-sito）,thermally oxidized beta-sitosterol（POPs）,and thermally oxidized cholesterol（COPs）to explore viability,morphology,cell cycle and mitochondrial membrane potential of Hep G2 cells.Results showed that the toxicity of these three sterol oxides to Hep G2 cells was 7K-sito>COPs>POPs at the different concentrations,indicating that 7-keto oxides are more sensitive to Hep G2 cell than thermal oxidation mixtures.All sterol oxides can significantly reduce cell viability,where 7K-sito had the highest activity and the most obvious reduction in cell viability.Moreover,all sterol oxides measured were concentration-dependent,which would increase early and late apoptotic cells and cause the cells to accumulate in the S phase.