Effect Of Carnosic Acid On Thermal Oxidation Stability Of Coconut Oil

Coconut oil is the main ingredient of coconut.Fresh and dried coconut kernel contain up to 33wt.%and 63wt.%oil content.It is not only an important tropical woody oil,but also a major product of international coconut processing.It is also a major product of international oil trade.It plays an important role in food,chemical industry and medicine,so it has attracted much attention in recent years.In the process of processing coconut milk,coconut sugar and coconut juice,the unsaturated fatty acid in coconut oil undergoes thermal oxidation and thermal isomerization to produce thermal oxidation products and trans fatty acids,which not only affect product quality,but also It can lead to security risks.Therefore,coconut oil was taken as the research object,and tert-butyl hydroquinone(TBHQ)oil samples were added as positive control to study the inhibition of carnosic acid on thermal oxidation and isomerization reaction of coconut oil.The aim is to provide technical support and theoretical basis for improving the quality of coconut products and the deep processing and utilization of coconut oil.(1)The national standard method was used to determine the changes of main physical and chemical indicators during the thermal processing of coconut oil.The results showed that the acid value(AV)and free fatty acid(FFA)of three groups of coconut oil increased gradually with the heating time prolonged,the peroxide value(POV)and total oxidation value(TOTOX)increased first and then decreased,and the malondialdehyde(MDA)and p-anisidine value(PAV)increased first and then tended to be gentle.The addition of antioxidants significantly reduced AV,FFA,POV,PAV,MDA,and TOTOX values in coconut oil samples(p<0.05).In the acid value and free fatty acid experiments,TBHQ and CA were equivalent;in the peroxide value and malondialdehyde experiments,TBHQ was better than CA.(2)Electron spin resonance(ESR)and high performance liquid chromatography(HPLC)were used to analyze the thermal oxidation products(aldehyde carbonyl compounds and free radicals)of coconut oil.The ESR signal intensity of the three groups of coconut oil increased with the prolongation of heating time.In the early stage(within 4 h),the effect of CA quenching free radicals was better than that of TBHQ.The TBHQ effect is stronger than CA in the later stage of heating.Among the five volatile aldehyde carbonyl compounds,the change of trans-2-decenoaldehyde content showed that the addition of antioxidants promoted the increase of its content at the later stage of heating,while the change of other substances content showed that the addition of antioxidants had obvious inhibitory effect,and the CA effect was better than TBHQ.(3)The thermal oxidation degradation products(main volatile components)of coconut oil were determined by thermal desorption instrument and gas chromatography-mass spectrometry(TD-GC-MS).From the analysis of the number of volatile components,adding antioxidants has delayed oxidation effect,and TBHQ is slightly better than CA.Among them,the relative content of aldehydes and alcohols increased first and then decreased;the relative content of ketones increased first and then tended to be flat;the relative content of acids and esters decreased first and then increased.Aldehydes and esters are the main volatile components The detection of a variety of characteristic small molecular substances indicates that oleic acid and linoleic acid have undergone oxidative decomposition.From the content of aldehydes,alcohols,acids and ketones,TBHQ is slightly better than CA.(4)The structure of coconut oil was analyzed by fourier transform infrared spectroscopy(FTIR),hydrogen spectroscopy('H NMR).FTIR analysis showed that CA could reduce the intensity of infrared absorption peaks of coconut oil trans-double bond substances and C=O bond characteristic groups and chemical bonds more effectively than TBHQ.'H NMR analysis showed that the unsaturated fatty acid decreased gradually with the heating time.Compared with TBHQ,CA has a slightly lower reduction in methylene peaks and unsaturated fatty acids(olefin hydrogen)at both ends of olefins in coconut oil.However,TBHQ was slightly stronger than CA in inhibiting the oxidation and decomposition of linoleic acid.(5)Differential scanning calorimetry(DSC)analysis of activation energy and kinetics showed that the E values of TBHQ and CA oil samples were about 3.3 and 2.2 times of those of blank group,respectively.(6)The composition of fatty acids and trans fatty acids was determined by gas chromatography-mass spectrometry(GC-MS).The results showed that the content of unsaturated fatty acids decreased gradually and the content of short and medium chain fatty acids increased.Long-chain saturated fatty acids increased first and then decreased.Compared with TBHQ,salvianolic acid can reduce the growth rate of palmitic acid and stearic acid,decrease the decline rate of oleic acid and linoleic acid,and inhibit the production of trans-oleic acid,trans-linoleic acid and trans-fatty acid.