Study On The Generation Law And Regulation Of Epoxy Triglycerides During Oil Thermal Processing

Epoxy triglycerides（ETGs）are a class of triglycerides that have at least one fatty acid acyl chain carrying an epoxy group.They are widely found in thermally oxidized oil and frying oil.ETGs are one of the most toxic components of oxidized triglycerides（ox-TGs）,having potential harm to human health.This paper established a comprehensive method for ETGs analysis to explore factors that affect the formation of ETGs during oil thermal processing,further achieved the targeted regulation of ETGs,and applied to actual frying systems.The main research contents and results are as follows:（1）An approach for ETGs qualitative analysis by high performance liquid chromatography-mass spectrometry（HPLC-MS）was developed by exploring the mass spectrometric decomposition rules of ETGs.The chromatographic and mass spectrometry conditions were optimized.ETGs were effectively eluted when the ratio of acetonitrile-water（6:4,v/v）to acetonitrile-isopropanol（1:9,v/v）was 37%to 90%.The optimal column temperature was 40℃,the flow rate of mobile phase was 0.3 m L/min.ETGs had the highest intensity in ESI positive ion mode,and the entire analysis process was completed within 20minutes.The accuracy of the method was verified.This method was of good linearity in the range of 0.20 to 1.00 mg/m L（R²=0.9971）.The average recovery rate was between 89.35%to105.01%.The detection limit and quantization limit were 0.0679μg/L,0.2032μg/L,respectively,indicating that this analytical method provided with good accuracy.Based on the characteristic fragments such as excimer ions,epoxy stearic aldehyde（m/z 281）,diacylglycerols such as OO⁺（m/z 603）,O_epO⁺（m/z 619）in mass spectrometry,a total of 36 ETGs were identified in thermally oxidized sunflower seed oil（SFO）,including five major categories（mono-ETGs,di-ETGs,hydroxy-ETGs,and aldehyde-ETGs）.（2）Influence factors that affect ETGs generation in vegetable oils were explored.Results showed that the total contents of ETGs were proportional to heating time,temperature,and degree of unsaturation of oil.At the early stage of heating,ETGs contents in palm oil（PO）,high oleic peanut oil（HOPO）,and SFO increased rapidly,but the cumulative rate decreased after 18 h.After heating at 120°C to 210°C for 36 h,ETGs contents in PO,HOPO,and SFO increased by 4.47 to 19.90,5.94 to 25.66,and 7.61 to 29.82 times,respectively,compared to fresh oil.Mono-ETGs and hydroxy-ETGs were the main monomers in PO and SFO,respectively（both above 40%）.The proportion of mono-ETGs increased with rising temperature and time.Other factors were investigated in SFO at 180℃.Results showed that ETGs total contents increased by 1.34 to 2.48 times as much as that of the control group（p<0.05）when air flow rate was rised from 30 to 120 m L/min.Metal ions（100 mg/kg）promoted ETGs formation（p<0.05）,and the promotion effect was inversely proportional to the valence state of added ions.Na⁺had the strongest promoting effect（33.87%）,while Al³⁺had the weakest（17.69%）.Compared with the control group,introducing water with a flow rate of 0.5 to 0.8m L/min to oil increased ETGs contents by 2.32%to 5.68%.Continue to reduce or rise water content prohibited ETGs formation（4.16%to 10.08%）.Adding 5%to 15%（oil weight）starch or 1%to 15%（oil weight）protein promoted ETGs contents by 4.47%to 22.5%and 17.69%to 51.32%compared to control group,respectively.However,ETGs contents were inhibited by low content starch（1%oil weight）at the early stage of heating（17.86%）,and then exceeded the control group with heating process.A prediction equation for ETGs contents was obtained using multiple linear regression analysis（R²=0.8574）.The total ETGs contents=0.747（heating time）+0.209（heating temperature）-0.007（water content）+0.216（protein content）+0.052（starch content）+0.474（air flow rate）.The correlation analysis between ETGs and oxidation indicators showed that ETGs were most correlated with ox-TGs（r=0.9522）,followed by TPC（r=0.9248）.（3）Tea polyphenol micelle particles were prepared to target inhibit ETGs in frying oil,and the flour coating quality was improved to reduce the migration of ETGs into food.The synergistic inhibitory effect of a 1:1 ratio of tocopherol and tea polyphenols on ETGs in SFO was the strongest（34.46%）.Tea polyphenol was embedded in lecithin high potency by evaporation film method.The particles size range was 107.00 to 752.79 nm,the Zeta potential range was-41.63 to-30.45 m V,and the encapsulation efficiency was between 64.86%to75.88%.Scanning electron microscopy showed that the micelle particles were spherical,and the laser confocal microscopy confirmed that the core material was successfully encapsulated and uniformly distributed in the wall material.Embedded tea polyphenol was mixed with tocopherols in a ratio of 1:1,and this combination had good dispersibility in SFO at both room temperature and high temperature.Its inhibition rate of ETGs in high-temperature SFO was46.94%higher than that of the non embedded group,and significantly superior to the effect of synthetic antioxidants.The inhibition rates of ETGs on the frying oil of fried chicken nuggets and french fries were 25.88%and 23.93%respectively,and the texture,sensory characteristics,and flavor substances of the samples did not significantly change compared to control group.In wheat flour coating system,with the increase of amylose/amylopectin ratio in the range of0.12 to 0.42,the coating ratio increased from 33.40%to 46.81%,and the oil contents in chicken nuggets decreased from 25.53%to 20.77%.Moreover,there was no significant difference in ETGs contents of the oil contained in chicken nuggets.Therefore,reducing oil absorption decreased the migration of ETGs into chicken nuggets,but when the ratio exceeded 0.29,the sensory quality of chicken nuggets significantly decreased.In summary,when amylose/amylopectin ratio in the powder coating layer is controlled to 0.29,combined with the application of micelle particle combination,it is expected to reduce the ETGs content in fried food by more than 33.95%.