Preparation Of Two Kinds Of Ferulic Acid Amides And The Evaluation Of Their Antioxidant Performance During Frying

During repeated frying,oils react with water,oxygen and food to cause rancidity,and antioxidants are usually selected to control lipid oxidation.However,common synthetic and natural antioxidants in commerce exert no good performance in deep frying,and are easily degraded and volatilized due to their poor thermal stability and volatility.Ferulic acid amide derivatives widely exist in nature,and they possess excellent thermal stability and strong antioxidant capacity.However,there are not enough ferulic acid amide derivatives in nature.This study payed attention to the synthesis of feruloylphenethylamine(FRP)and feruloyltyramine(FTP).Their antioxidant properties during frying were investigated,and underlying antioxidant mechanisms were also speculated.The main content are as follows:FRP and FTP were synthesised from ferulic acid through(benzotriazol-l-yloxy)-tris-(dimethy lamino)-phosphonium hexafluorophosphate(BOP)coupling by chemical method.The struct-ure of FRP and FTP was confirmed by liquid chromatography-mass spectrum(LC-MS)and proton nuclear magnetic resonance(’H-NMR).The purity of FRP and FTP was 97.05%and 94.55%,respectively,determined by high performance liquid chromatography(HPLC).Firstly,soybean oil is used as frying oil,by comparing the change of acid value,total polar component and its composition in frying oil to verify the relationship between the rapid evaluation method and the actual frying.The results showed that this rapid method was in agreement with the deterioration degree of oils in actual frying.So it can be used to evaluate the stability of the frying oil directly.Based on the rapid evaluation method of the stability of frying oil,the optimum application concentration of FRP and FTP in frying oil were studied,and their antioxidant properties were evaluated.It is shown that the soybean oil fortified with 500 mg/kg FRP or FTP exhibited the best inhibitory effect on deterioration of frying oil.The total polar component was increased by 19.16%and 8.61%compared with those in the blank group(without adding antioxidants in the soybean oil).Subsequently,the antioxidant performance of FRP and FTP was compared with common antioxidants,and formula antioxidant effects during frying was studied.The order of antioxidant performance(500 mg/kg antioxidant,frying 120 min at 180 °C)was FRP>ascorbyl palmitate>FTP>ethyl ferulate>rosemary extract>γ-oryzanol>BHT>tocopherol>ferulic acid>tea polyphenol palmitate,indicated by the content of total polar component as an indicator.FRP exerted the best antioxidant activity(P<0.05).The antioxidant activity of FRP and FTP were significantly stronger than BHT.The TGP content of FRP and FTP was relatively low(16.0%and 20.1%,respectively).FRP showed excellent anti-polymerization ability.The formula antioxidant results showed that the best antioxidant activity of formula antioxidant was obtained when the content of FTP and tea polyphenol palmitate(TP)was both 250 mg/kg.The content of total polar component in formula antioxidants was 28.1%through rapid frying for 120 min,which was slightly stronger than the total polar component(containing 28.8%TBHQ).Finally,the content of aldehydes was traced by 1H-NMR in the frying system added with single antioxidant.The results showed that the content of aldehydes during frying in soybean oil containing FRP and FTP(18.36 mmol/mol TAG and 20.97 mmol/mol TAG,respectively),which was decreased by 19.68%and 8.27%compared with y-oryzanol.Previous studies showed phenolic acid amides had the mechanism of removing aldehydes besides the free radical mechanism.Therefore,it was most likely that ferulic acid amides can remove aldehydes from the frying oil through a condensation reaction between amine and carbonyl group,thereby inhibiting deteriorating of deeq frying.