Qualitative And Quantitative Analysis Of Aldehydes In Vegetable Oils And Its Study On Control Techniques

Most vegetable oils are rich in unsaturated fatty acids,which are easily oxidized,leading to rancidity,odors and discoloration.In order to delay these degradation reactions,exogenous additives are usually added to vegetable oil.Importantly,aldehydes are the main secondary oxidation products of vegetable oil.The qualitative and quantitative determination of aldehydes is the premise for the smooth progress of antioxidant research of vegetable oil.In view of this,sunflower oil(rich in linoleic acid)was selected as the main research object,and the qualitative and quantitative determination methods of aldehydes were optimized and verified.On this basis,the oxidation inhibition effects of L-ascorbyl palmitate(AP),carnosic acid(CA)and vitamin E(VE)on sunflower oil under single and combined conditions were studied.This work can provide scientific data and technical support for the quantitative determination of aldehydes and the control of aldehydes formation.The main research results are as follows:(1)A reliable RP-HPLC method for the determination of carbonyl compounds was developed,and 2,4-decadienal as the target aldehyde was verified and applied.The optimal sample pretreatment method was extraction by 2 m L of acetonitrile three times,followed by derivatization at 40°C for 30 min.The method was linear,sensitive,and accurate with detection and quantification limits of 15 and 50 nmol/L,respectively,and had good average recoveries for 2,4-decadienal in oil samples.In tested edible oils,during heating at180°C,the level of 2,4-decadienal rose faster than other aldehydes,including one of the characteristic aldehydes,hexanal.In addition,after accelerated oxidation,the content of2,4-decadienal in the systems of sunflower oil,corn oil,soybean oil and blend oil was correlated with other oxidation indices(R~2=0.81 to 0.97 for p-AV;R~2=0.83 to 0.97 for TOTOX,indicating that 2,4-decadienal can predict the oxidative deterioration of oil.(2)The oxidation inhibition of sunflower oil with different concentration of AP and CA was investigated.The results showed that a dose-response relationship existed in AP.The lowest values of anisidine(p-AV),total oxidation value(TOTOX),conjugated diene(CD)and 2,4-decadienal were reached at 200 ppm 4 h before heating at 150℃.After heating for 24 h,200ppm-AP still had a stabilizing effect on linoleic acid.The dose-response relationship also existed at 4h before heating at 150℃,and the best effect was at 200 ppm.(3)The antioxidant properties of AP and CA on sunflower oil were compared under the optimal concentration.The oxidation induction time of carnosic acid in sunflower oil showed that the oxidation induction time of carnosic acid at five temperatures(80,90,100,110 and 120℃)was about 10 times that of AP,indicating that CA could replace AP in sunflower oil.(4)The antioxidant capacity of sunflower oil was investigated by adding AP,CA and VE into sunflower oil at different concentrations.The results showed that the antioxidant efficacy was different under different heating time and different types of antioxidants.VE showed significant inhibitory effects on oxidative indices such as p-AV,CD,CT,TOTOX and aldehydes(e.g.,2,4-decadienal)at low concentration(200 ppm)and short time(within4 h),but weak at high concentration(800 ppm).VE and CA complex,CA and AP complex have the most potential for pair antioxidant complex.The three kinds of compound showed stronger antioxidant effect.In general,all antioxidant combinations added with CA had a good effect on the oxidation stability of sunflower oil.Among them,the sunflower oil added with 200 ppm CA+200 ppm AP+800 ppm VE showed the highest oxidation stability in all heating time and all indexes,and had a great potential for application in food industry.