Antioxidant Effect Of Tocopherol-loaded Ethyl Cellulose Particles In High-temperature Oil

Frying oil is an important source of lipid in the diet.It not only contains abundant fatty acids,but also makes frying food crispy,which is popular with consumers.Oxidation,hydrolysis and polymerization occurs during heating at 150 °C to 190 °C,resulting some adverse products.Tocopherol is a kind of natural antioxidant,but it tends to degrade at high temperature,reducing its antioxidant capacity to a large extent.It is well-known that encapsulation is one of the most effective ways to protect antioxidant from heat and oxygen.Some researchers tried to encapsulate natural antioxidants to inhibit thermal oxidation of edible oils.But there were still two main limitations about the previous researches: The evaluation temperature of above experiments was lower than the commonly applied processing temperature and the fabricated microcapsules were not well dispersed in oil system.Based on the above limits,ethyl cellulose,a heat resistant hydrophobic polymer,was applied to encapsulate tocopherol,aiming to inhibit thermal oxidation of soybean oil,decrease contents of adverse products and prolong the service time of frying oil.Firstly,we fabricated the tocopherol-loaded particles by ethyl cellulose differing in viscosity and the physicochemical properties of them were characterized.Next,the antioxidant effect of different loaded particles on soybean oil was fully evaluated.Furthermore,the antioxidant mechanism of the loaded particles was explained.The main results were listed as follows:By anti-solvent method,tocopherol was successfully encapsulated by ethyl cellulose with different viscosities(9cP,70 cP and 200 cP)and the physicochemical properties of the obtained loaded particles(EC9-T?EC70-T and EC200-T)were characterized.As the viscosity of ethyl cellulose increased,particle size decreased from 72596 nm to 245 nm,Zeta potential decreased from-24.37 mV to-41.50 mV.Through scanning electron microscope images,it could be seen that the loaded particles were round and slight aggregation occurs among them.Confocal laser scanning microscope further confirmed successful encapsulation and uniform distribution of tocopherol in the loaded particles.Encapsulation efficiency and loading capacity of the loaded particles were 88.72%?99.71% and 22.18%?24.93%,respectively.Thermogravimetric analysis confirmed that loaded particles protected tocopherol from thermal degradation at 277.3°C.And differential scanning calorimetry analysis indicated that ethyl cellulose with viscosity of 70 cP and 200 cP successfully protected tocopherol from oxidation at 150 °C.To explore the antioxidant application of the loaded particles in soybean oil,their dispersibility and antioxidant effect were evaluated.Three kinds of loaded particles(EC9-T,EC70-T and EC200-T)had good dispersibility in soybean oil and decreased the viscosity,K232(absorbance at ?=232 nm),K268(absorbance at ?=268 nm),acid value,total polar compounds content,carbonyl value,p-anisidine and volatile(E,E)-2-4-heptadienal content of soybean oil.There was no significant difference in antioxidant effect between EC9-T and EC70-T loaded particles,and EC200-T was the most effective in inhibiting thermal oxidation.In detail,EC200-T loaded particles decreased the total polar compounds content,carbonyl value and p-anisidine of soybean oil by 44.29%,46.94% and 35.43% respectively compared to the control group.According to the legal limit of total polar compounds content in state criteria for food safety(27%),EC200-T increased the service time of heated soybean oil approximately from 20 h to30 h,which performed far better than tert-butylhydroquinone and rosemary extract.The antioxidant mechanism of the loaded particles was explained.Through Fourier transform infrared spectroscopy,it was found that ethyl cellulose and tocopherol interacted with each other by hydrogen bond.The loaded particles delayed the thermal degradation of tocopherol in soybean oil and increased the retention rate of total tocopherols from 25.04% to57.45% after heating for 20 h.Correspondingly,loaded particles significantly increased the antioxidant effect of tocopherol in high-temperature soybean oil.In addition,ethyl cellulose with viscosity of 200 cp could inhibit thermal oxidation of soybean oil.It was predicted that ethyl cellulose exhibited antioxidant effect by being oxidized at high temperature and consuming oxygen in the oil system.The prediction was further proved by investigating the effect of pre-oxidation,temperature and oxygen on the antioxidant activity of ethyl cellulose.In the last,the potential antioxidant mechanism of the loaded particles was explained: On the one hand,tocopherol was entrapped in the network of loaded particles,ensuring that it was protected by physical barrier and decomposed at a slower rate;On the other hand,ethyl cellulose and tocopherol acted on different stages of oxidation,played a complementary role to exhibit antioxidant effect together.