Effect Of Rosemary-based Antioxidants On The Oil Quality During Deep Frying Of French Fries

Frying is one of the common methods in food processing.Fried foods are widely favored by consumers because their unique sensory characteristics.However,high temperature processing will cause oxidation and deterioration of oils,leading the production of oxidation products which are harmful to human health.In this study,quality changes of different vegetable oils were explored during deep-frying process.The relationship between oil types,frying condition and chemical indicators was established,which provides a basis for predicting the quality of frying oil.In addition,the antioxidative effect of rosemary antioxidants were detected using rapid methods.At the same time,the solubility of rosmarinic acid as a polar antioxidant derived from rosemary was measured,which could provide a theoretical basis for its use in oils.The main content is as follows,(1)Changes of chemical parameters like acid value,viscosity,and total polar compounds in soybean,palm and rice bran oil were detected during deep-frying process and a rapid prediction system for its quality were established.The results showed palm oil had the best frying quality,followed by rice bran oil and soybean oil.The concentration of oryzanol decreased from 144.84 to 73.10 mg/L(not detected in palm oil and soybean oil)in rice bran oil during deep frying,and meanwhile,rice bran oil showed better DPPH free radical scavenging ability than palm oil and soybean oil,resulting in its good frying quality.Based on the quality changes of oils above,the dynamic viscosity changes of soybean oil,palm oil and rice oil at different temperatures were analyzed and found to fit with Lioumbas equation(R~2>0.999).The relationship among oil types,frying time and oil chemical composition was established using empirical parameters of the model with the prediction accuracy of 90%(R~2>0.97).This equation might provide a new method for rapid predictions of quality changes in frying oils.(2)The effect of different rosemary-based antioxidants(rosemary extracts,carnosic acid,rosmarinic acid)on soybean oil was explored during continuous frying French fries.Oil quality was characterized by traditional chemical indexes combined with low field nuclear magnetic resonance(LF-NMR)and near infrared spectrometry(NIRS)as rapid monitoring methods.The results showed that natural antioxidants from rosemary were better than synthetic antioxidant during deep frying(antioxidative effect:rosmarinic acid>rosemary extract>carnosic acid>TBHQ>control),which was consistent with the polar paradox theory that the polar antioxidant was better than other non-polar antioxidants.The results of multivariate analysis of LF-NMR and NIRS were consistent with the traditional chemical value,which not only proved rosmarinic acid as the potential natural antioxidant in frying oil application,but also showed the potential application of LF-NMR and NIRS as fast and non-destructive methods in fried food industries.(3)The interaction of rosmarinic acid and oryzanol in oil was studied,as well as.the solubility and thermodynamic variables of rosmarinic acid in soybean oil at 293.2-318.2 K.The results showed that the antioxidative effect of rosmarinic acid was up to92.83%,which had better antioxidative effect than oryzanol and no synergistic effect was found between them,which proved again the polar paradox theory.Polar antioxidants have better effects in soybean oils.The solubility of rosmarinic acid in soybean oils increased from 293.2 K to 318.2 K.At the same time,Apelblat model(RD<0.1)and Arrhenius equation(error<10%)were used to fit the dissolution process,where theoretical values had a good correlation with experimental values.According to the Apelblat model,the dissolution of rosmarinic acid in soybean oil was a non-spontaneous heat absorption process with an increasing thermal stability based on thermodynamic parameters of rosmarinic acid.