Effects Of Different Roasting Conditions On The Structure Of Polysaccharides In Sesame Skin Cell Wall

Sesame(Sesamum indicum L.)is an important oil crop.Sesame oil is the main product of sesame processing in China and the world.Roasting pretreatment,as a key step during the process of fragrant sesame seed oil,has complicated various chemical reactions,which made the fragrant sesame oil have rich aromas and characteristic colors as well as antioxidant activities.Many sugar compositions,which provided by the dissociation of cell wall polysaccharides in sesame seeds during the roasting pretreatment process,were the important precursors for sugar chemical reactions including the Maillard reaction and caramelization.Sesame skins are an important part of sesame seeds which is rich in carbohydrates,especially cell wall polysaccharides such as cellulose,hemicellulose,and pectin.However,there are few reports about polysaccharides in the cell wall of sesame skin.In this paper,the cell wall polysaccharides from sesame skin before and after roasting were extracted and characterized.It is expected to provide theoretical supports for the study of Maillard reaction and caramelization reaction in sesame seed roasting pretreatment and the comprehensive utilization of sesame skin cell wall polysaccharides.The main research contents and conclusions are as follows:1.The changes of main ingredients in sesame skin were studied under different roasting conditions.The fatty acid composition,amino acid composition and monosaccharide composition of the sesame skin remained unchanged during the roasting process.The polysaccharides mainly included cellulosic polysaccharides,hemicellulosic polysaccharides and pectinic polysaccharides in the sesame skin.The sesame skins were aromatic odor after roasting,which were derived from furan,furfural,pyrimidine,thiazole,pyrrole,pyridine and other substances produced in the process of the Maillard reaction and caramelization.The contents of serine,threonine,arginine,galacturonic acid,rhamnose,arabinose and xylose in the roasted sesame skin decreased sharply.It was speculated that its may as an important precursors in the Maillard reaction and caramelization reaction.2.The changes of cellulosic polysaccharides in sesame skin were studied under different roasting conditions.The hemicellulosic sugars attached to cellulose,such as galacturonic acid,xylose and rhamnose,were more easily degraded than other sugars.Although,during roasting,the crystalline structure and linkages of these sugar units in cellulose did not obviously break down,amorphous cellulose did partly degrade.The sugars were degraded to various volatile compounds,such as acetic acid and 3-furaldehyde,were likely contributors to the Maillard and caramelization reaction in sesame seed roasting.3.The changes of hemicellulosic polysaccharides in sesame skin were studied under different roasting conditions.The yield of hemicellulose increased after sesame skin roasting.The side chain sugar units of hemicelluloses in the cell wall structures were more easily breaked and degraded as compared with the main chain structure.The degradation of xylose,arabinose and rhamnose in hemicellulose may contribute to the Maillard and caramelization reaction,thus affecting the flavor and color of sesame oil.4.The extraction and analysis of pectin polysaccharide from sesame skin were carried out in this chapter.The structure and composition of pectin in sesame skin were understood comprehensively,which provided theoretical and technical support for the subsequent study of its degradation.Three pectin components,SSP30(DE=44.62%),SSP50(DE=36.70%)and SSP90(DE=22.73%),were all low methoxypectin extracted from sesame skin.Among the pectin samples,SSP30 had the highest yield(7.35%),the highest content of galacturonic acid(76.39%),the highest degree of esterification(44.62%)and the highest molecular weight(41531 Da).SSP50 had the lowest yield(0.68%).However,it had the most complex composition of monosaccharide.In addition,thermogravimetric analysis showed that SSP50 had the highest thermal stability.SSP30 had greater viscosity,foam stability and emulsification stability at high concentration(?2.0%).SSP30 had the highest scavenging ability of hydroxyl radical in vitro tests of antioxidant activity.5.The changes of pectinic polysaccharides in sesame skin were studied under different roasting conditions.The yield of pectin increased when sesame skin was roasted at low temperature(?180?),while high temperature roasting(?200?)caused a decreasing in the yield.The RG-I region and side chain sugar units of pectin were more easily degraded during the roasting of sesame skins.The degradation of rhamnose,arabinose,galactose,fucose,xylose and glucuronic acid in pectin may contribute to the Maillard and caramelization reaction,thus affecting the flavor and color of sesame oil.According to the research of this subject,it can be understood that hemicellulosic polysaccharides and pectin polysaccharides were more likely to be degraded than cellulose polysaccharides in sesame skin.And their degradation products participated in Maillard reactions and caramelization reactions as important precursors.And then the flavor and color of sesame oil were affected.