Study Of The Antioxidant Effect Of Rosemary Extract In Chicken Fat And Its Emulsion

Rosemary(Rosmarinus officinalis L.)extract(RE)is a natural and effective antioxidant extensively used in oils,fats and meat products while the relationship between its stability and antioxidant effect in thermal processing remains unclear.Besides,the mechanisms of the antioxidant effect of RE on the lipids in protein emulsions are not specified yet.This research firstly studied the antioxidant effect,thermal decomposition characteristics and total phenolic content after heating of RE,and the changes in the content of bioactive compounds were analyzed.Later RE was applied in chicken fat to study its antioxidant effect and protective effect on the physical properties of chicken fat at 90-150℃.Next,myofibrillar protein(MP)-chicken fat emulsion was prepared,and the concentration-related antioxidant effect of RE on this emulsion along with its mechanisms were discovered.The main contents and conclusions are as following:1.RE shows favorable free radical scavenging and reducing ability,which increase with its concentration,but RE cannot form chelates with metal ions;2.The simultaneous thermal analysis(TG-DTA)shows that RE first decomposes at 200 ℃in air atmosphere while the phenolic compounds are easily destroyed beyond 130 ℃,which indicates the greater sensitivity of bioactive compounds though RE is stable at high temperatures;3.The antioxidant characteristic of RE becomes more distinct with increasing heating temperature and time at and below 130 ℃,which endows chicken fat with better oxidative stability.Also the TG-DTA result shows that RE promotes the thermal stability of chicken fat by preventing oxygen absorption and elevating the initial decomposition temperature of chicken fat;4.The preparation and storage condition have significant influence on the oxidative stability of MP-chicken fat emulsion.Emulsions stored at low temperature(4℃)are prone to oxidation and the different concentrations of RE have no impact on its oxidative stability.Besides,RE has no antioxidant effect on emulsions stored at room temperature(25℃)and the concentrations of RE show no significant difference(p>0.05)in enhancing its oxidative stability;5.The influence of RE on the molecular structure and emulsifying properties of MP and on the physiochemical characteristics of MP-chicken fat emulsion were studied,and the results reveal that the phenolics in RE are connected with MP through covalent and non-covalent bond,which consequently modifies the structure and properties of MP and decreases the amount of available phenolic hydroxyl groups.Therefore,the antioxidant effect of RE on MP-chicken fat emulsion is eliminated.6.The DSC results show that high concentrations(0.2% and 0.4%)of RE elevate the melting point of chicken fat and as a result the solid fat content at the same temperature increases,which causes the unobvious antioxidant effect of RE.