Study On Inhibition Mechanism Of Carnosic Acid On Formation Of Trans Fatty Acids In Oils And Fats During Heat Tratment

Trans fatty acids(TFAs)in edible oils during heating processing are a risk factor for the human health.Reduction of TFAs formation in food product can improve the food safety.Previous studies suggested that natural antioxidants can reduce the formation of trans fatty acids in edible oils during heat treatment.Fully understanding of the inhibition mechanism of natural antioxidants is the main challenges in developing low dietary TFAs food products.Previous studies have showed that carnosic acid(CA)can significantly reduce the TFAs content via free radical scavenging to prevent thermal oxidative degradation and heat-induced isomerization reaction.In this proposal,the quantum chemistry density functional theory(DFT)will be used for the theoretical calculation of the effects and transition state of eliminating free radical reaction to elucidate their theoretical mechanism.The oleic acid triacylglycerol/carnosic acid model system will be used to explore inhibitory pathway and kinetics characteristic of carnosic acid.Moreover,frying food system using coconut oil will be chosen to discuss the inhibitory effects of carnosic acid on TFAs formation in different heat processing conditions.These results may provide insight into the role of carnosic acid during heat treatment and may suggest the way to reduce the formation of TFAs.This thesis includes five research part,whose main results are followed.Firstly,density functional theory(DFT)was used to analyze the CA's antioxidant activity mechanism by theoretical calculating the indicators such as atomic charge,total molecular energy,and phenolic hydroxyl dissociation enthalpy(BDE),the highest occupying orbit(HOMO)energy,and the lowest altitude orbit(LUMO)energy by B3LYP/6-31G(d,p).In vitro antioxidant activity of carnosic acid was analyzed by DPPH,ABTS and retroactivity test.The results showed that the two phenolic hydroxyl groups at the C7(O15)and C8(O18)sites on the benzene ring of CA had the highest activity,and the reaction heat was minimal when hydrogen extraction occurred.Among them,phenol hydroxyl activity of C7(O15)(303.34 kJ/mol)was slightly lower than that of C8(O18)(295.63 kJ/mol),while dissociation enthalpy of phenol hydroxyl was much lower than that of ?-CH2 bond(C8,353.92 kJ/mol and C9,353.72 kJ/mol).The results of theoretical calculation on antioxidant activity were consistent with those of in vitro assays.Secondly,the analysis results of the national standard method,hgh performance liquid chromatography(HPLC),fourier transform infrared spectroscopy(FTIR),electron spin resonance(ESR)and Hnuclear magnetic resonance spectroscopy(1HNMR)showed that the addition of antioxidants could significantly reduce the main characteristic indexes free fatty acids(FFA),acid value(AV),peroxide value(POV),p-anisidine value(PAV),and total oxidation value(TOTOX),and inhibit the production of major aldehyde carbonyl compounds and free radicals.Among them,CA had slightly better inhibitory effects on FFA,AV and free radicals of oleic acid triacylglycerol than Tertiary butyllhydroquinone(TBHQ).Infrared spectral analysis showed that CA was better than TBHQ to reduce infrared absorption of compounds containing characteristic groups and chemical bonds,such as the non-conjugate C=C bond,C-H-bound cis-/trans-double bond,methylene and methyl,and C=O bond.The HNMR analysis showed that CA reduced slightly lower on methylene and unsaturated fatty acids(olefin hydrogen)than TBHQ.This indicated that CA had a strong inhibitory effect on the thermal oxidation of oleic acid triacylglycerol.Thirdly,Rancimat method and non-isothermal differential Scanning calorimetry(DSC)method got the results of activation energy and Kinetics analysis.CA was better than TBHQ to prolong oxidation induction period and to reduce reaction rate of oleic acid triacylglycerol.According to Arrhenius equation,the apparent activation energy(Ea)of CK,CA,and TBHQ oxidation reaction was 82.23,93.12 and 92.44 kJ/mol,respectively,indicating that antioxidants could improve the apparent activation energy and thermal oxidation stability of oleic acid triacylglycerol in thermal oxidation reaction.Using the Flynn-Wall-Ozawa method and Kissinger-Akahira-Sunose method also proved that adding CA and TBHQ could increase the thermal oxidation stability of oleic acid triacylglycerol,and the CA had a better effect than TBHQ.The inhibition of oleic acid triacylglycerol to form trans oleic acid fit the zero-order kinetic equation.CA can significantly reduce the reaction rate than TBHQ,and CA can reduce the reaction rate of methyl oleate to form trans oleic acid,indicating that CA inhibits the formation of methyl oleate.The isomerization reaction is stronger than TBHQ.Fourthly,the analysis results of the national standard method,HPLC,fourier FTIR,ESR and HNMR showed that CA could significantly reduce the FFA,AV,POV,PAV,and TOTOX values of Camellia oil,and could inhibit the production of major aldehyde carbonyl compounds and free radicals.Infrared spectral analysis showed that TBHQ reduced more infrared absorption of substances containing characteristic groups and chemical bonds,including C-H bond,cis-/trans?double bond,and C=O bond than CA.The NMR analysis showed that CA reduced slightly more on methylene and unsaturated fatty acids(olefin hydrogen)than TBHQ.The results showed that CA had a strong inhibitory effect on the thermal oxidation of in Camellia seed oil system.Fifthly,the results of Rancimat method and non-isothermal DSC method also showed that CA had significantly better effects than TBHQ to prolong oxidation induction period and to reduce reaction rate of Camellia oil.The Ea of CK,CA,and TBHQ oxidation reaction was 93.50,106.00 and 94.56 kJ/mol,respectively,indicating that antioxidants also could improve the apparent activation energy and thermal oxidation stability of Camellia oil.Using the Flynn-Wall-Ozawa method and the Akahira method got the similar results,and it showed a good correlation(R2>0.95).CA could reduce more the growth rate of palmitic acid,stearic acid,and oleic acid,the decline rate of linoleic acid and linolenic acid,and inhibit more the production of trans-oleic acid,trans-linoleic acid and trans-fatty acid than TBHQ.