Study Of Thermal Reactions Between Sesame Carbohydrates And Protein In The Maillard Model System

Roasting seeds is one of the key pretreatments to produce aromatic vegetable oils.The high-temperature treatment changes the texture properties of the seeds and gives aroma and good color,which are related to the complex reactions induced by roasting,particularly the Maillard reaction.Protein and non-starch polysaccharides are important components in sesame,having a great contribution to color and flavor during roasting.In this study,to investigate the participation of macromolecules in the Maillard reaction and their contribution to color and flavor formation,the polysaccharide-protein model system and the oligosaccharide-protein model system were firstly established,and the substrate consumption,browning intensity,and volatile compounds were determined.Then the typical amino acids were chosen to establish the polysaccharide-amino acid model system and the oligosaccharide-amino acid model system,to further investigate the effect of specific nitrogen sources reacted with sugars on color development and flavor formation.The main content and conclusion are shown below.1.Sequential fractionation and characterization of structural polysaccharides extracted from sesame:Five cell wall polysaccharides（WSP,CSP,NSP,KS1,and KS4）were obtained from sesame hull using water,chelator（CDTA）,Na₂CO₃,1 mol/L KOH and 4 mol/L KOH,respectively,and their structural and functional properties were investigated.WSP and CSP were rich in galacturonic acid,approximately 30%and 70%,respectively.They were pectic polysaccharides with a backbone consisting ofα-D-1,4-Galp A units,mainly existing in middle lamella and primary cell wall.The polysaccharides extracted with lye were hemicellulose,which existed in the secondary cell wall.WSP and CSP were susceptible to thermal treatment and began to degrade at 150°C,which were the key carbonyl precursors to participate in thermal reaction.2.Thermal reaction between sesame structural polysaccharides and proteins:WSP and CSP were chosen as thermally unstable substrates to build the Maillard model system with sesame isolate protein（180°C,35 min）,to investigate their reactivity of color development and flavor formation.TGA showed that SPI had higher thermal stability than WSP and CSP,which reached the highest degradation rate at 300°C.The content of total sugar and protein decreased significantly after roasting.Glucose,galacturonic acid,lysine,and arginine significantly reduced and they were the key monomers involved in thermal reaction.CSP and SPI mixture had higher thermal reactivity according to color development and browning intensity.After roasting,the content of aldehydes（45%-75%）and heterocyclic compounds（20%-35%）increased significantly.3.Thermal reactions between sesame structural polysaccharides and amino acids:several amino acids（lysine,arginine,methionine,cysteine and serine）were chosen to establish the Maillard model system with WSP and CSP（180°C,30 min）.TGA showed that lysine and arginine had the lowest thermal degradation rates（<15%/°C）,which offered more carbonyl sites for the Maillard reaction.CSP had higher thermal reactivity with amino acids than WSP,and the highest reduction rate of total sugar was 45%.CSP and lysine/arginine showed significant color development after roasting,exceeding the color development of polysaccharides-protein model system.The volatiles were mainly aldehydes and heterocyclics after roasting.Except for cysteine（12.9%）,heterocyclic compounds accounted for about 75%of all other mixtures.Pyrazines,pyrrole,and pyridine were the predominant volatile compounds,which were the key characteristic aromas in sesame oil.4.Thermal reaction characteristics of sesame oligosaccharide and protein:the model system was established by sesame oligosaccharides and protein to investigate the formation of color and flavor（160/180°C,5/10 min）.TGA showed that SOL began to degrade approximately at 100°C and reached the highest degradation rate at around 207°C,which was thermally unstable than SPI.Color and browning intensity significantly increased with increasing roasting intensity,and lysine,arginine,cysteine,galactose and fructose were the key monomers involved in the thermal reaction.The type and concentration of volatiles increased significantly with increasing roasting intensity,and esters,heterocyclics and phenolic compounds were the main volatiles,account for 3.2%-29.8%,14.1%-34.2%,and28.4%-32.3%,respectively,which was higher than that of WSP/CSP-SPI model system but lower than the WSP/CSP-amino acid model system.5.Thermal reaction between sesame oligosaccharides and amino acids:the significantly reduced amino acids（lysine,arginine,cysteine,serine,tyrosine,and aspartic acid）were chosen as substrates to establish a model system with SOL（120°C,15 min）.TGA shows that tyrosine is highly thermal stable and began to degrade at 300°C.However,aspartic acid showed a clear stepwise degradation phase.Lysine and arginine were specially reacted with galactose,the same for aspartic acid and fructose.The color and browning intensity largely developed after heating（ΔE>20）,and more heterocyclic compounds（3.2%-29.9%）were produced from the SOL-amino acids model system,which was higher than the oligosaccharide-protein model system but lower than the polysaccharide-amino acid model system.In a summary,this study found that the color development and flavor formation were significantly different in various model systems.The formation of flavor from strong to weak was that polysaccharide-amino acid model system,oligosaccharide-amino acid model system,oligosaccharide-protein model system,and polysaccharide-protein model system.Glucose,galactose,galacturonic acid,lysine and arginine were the key monomers involved in the thermal reactions.Moreover,sulfur-containing amino acids including methionine and cysteine inhibited the Maillard reaction.This study gives a new idea to investigate aroma formation of sesame oil,as well as providing a theoretical reference for preparing spice by thermal reaction.