Effect Of Sesame Oil And Fatty Acids On Thermal Reaction Volatile Compounds From Defatted Sesame Meal

Sesame is one of the important oil crops.And sesame oil has been the favorite of consumers for its rich unique flavor.Volatile compounds have a decisive effect on the unique flavor of roasted sesame and sesame oil.As the richest component of sesame,lipid also is one of the important aroma precursors which play a critical role of the characteristic flavor of sesame oil.This research focuses on the effects of lipids on the formation of roasted sesame meal flavour,taking the defatted sesame meal,cold-pressed sesame oil and five major fatty acids as materials.Gas chromatography(GC)was used to analyze the fatty acid composition in cold-pressed sesame oil and oxidized cold-pressed sesame oil.Using solid phase microextraction-gas chromatography-mass spectrometry(SPME-GC/MS)technology combined with sensory evaluation to optimize the thermal reaction conditions of defatted sesame meal.The impacts of oxidized and non-oxidized cold-pressed sesame oil on the volatiles of defatted sesame meal Maillard reaction were analyzed by establishing different reaction model systems.We studied the thermal oxidation products of five fatty acids.In addition,the effects of different fatty acids on the defatted sesame meal thermal reaction systems were also investigated.The main contents and results of this paper are as follows:1.The composition and content of volatile components observed from roasted defatted sesame meal with different reaction conditions were detected by SPME-GC/MS.Meanwhile,the thermal reaction products were evaluated by sensory evaluation.Results showed that the optimal Maillard reaction conditions were: defatted sesame meal which had 15% moisture content,reacted at 120°C for 15 min.Under this condition,a total of 57 aroma compounds were identified,including 26 components with S-,N-or O-heterocycles which had higher contents.And at this time,the roasted defatted sesame meal was fragrant,golden in color,and high quality.2.First,The fatty acid compositions in cold-pressed sesame oil and oxidized cold-pressed sesame oil were analyzed by GC.Results showed that linoleic acid,oleic acid,palmitic acid and stearic acid were the main fatty acids in sesame oil,and a decrease in linoleic and polyunsaturated fatty acids values was observed after thermal oxidation.Then we examined the flavour profiles of thermal reaction mixtures including oxidized and non-oxidized cold-pressed sesame oil by SPME-GC/MS.The addition of sesame oil to the defatted sesame meal resulted in an increase in the types and amounts of volatile components.However,general Maillard reaction products were inhibited or in low content.In addition,numerous thermal degradation components of sesame oil appeared and interaction compounds of Maillard reaction with lipid degradation products were formed.Compared with cold-pressed sesame oil,controlled oxidized sesame oil had more obvious effect on the Maillard reaction products.It showed that the volatiles' amounts was higher,as well as the contents of aldehydes,phenols,pyrazine,pyridine,pyrrole and furans which made important contributions to the flavour of roasted sesame.There was a more significant decrease in the sulfur-containing compounds,and the contents of several heterocyclic compounds with long-chain alkyl substituent were also higher.3.GC/MS was used to investigate the thermal oxidation products of five major fatty acids in cold-pressed sesame oil.Results showed that aldehydes,ketones,alcohols,acids,esters,hydrocarbons and furans were the main products of thermal oxidized fatty acids.Among them,aldehydes were the most abundant components,which accounted for the main part of the thermal degradation products.Compared with saturated fatty acids,unsaturated fatty acids were more easily oxidized to produce more volatiles which made them have more influence on the flavour of controlled oxidized sesame oil.4.This section aimed to study the effects of 5 fatty acids on volatile compounds in the thermal reaction system of defatted sesame meal by using SPME-GC/MS.We have chosen palmitic acid,stearic acid,oleic acid,linoleic acid and linolenic acid for the investigation.The results showed that compared with defatted sesame meal system,the addition of fatty acids resulted in an obvious increase in the types and levels of thermal reaction products,and promoted the formation of pyrazines,pyridines,furans and thiophenes.Different fatty acids with different contents had certain influences on the composition and contents of volatile thermal reaction products.Besides,saturated and unsaturated fatty acids had significant different effects on the volatiles.Oleic acid and linoleic acid are two of the richest unsaturated fatty acids in cold-pressed sesame oil.And linoleic acid-defatted sesame meal system had more thermal reaction products than the system containing oleic acid.Because of the extremely low content,the addition of linolenic acid didn't have an obvious effect on the volatiles.And in comparison with the palmitic acid-defatted sesame meal system,the reaction of stearic acid and defatted sesame meal produced more compounds,which made it have more influence on defatted sesame meal aroma.Principal component analysis showed that the effect of linoleic acid on the volatile products of the basic thermal reaction system of defatted sesame meal was more consistent with that of sesame oil,and its contribution to the flavour of roasted sesame was the largest of 5 fatty acids.