Maillard Reaction Of Three Free Amino Acids-glucose Under Mild Conditions

Maillard reaction plays an indispensable role in the food industry.Since the reaction process is complicated,most researchers establish a single reaction model to simplify substrates at the beginning of the study,which using a single sugar reacting with amino acid,through controlling reaction conditions,to investigate the properties and functions of the reaction products.At present,studies on high temperature(>100℃)Maillard reaction are mature,in which most of them are focused on flavor compounds,browning reactions,flavoring and anti-oxidation characteristics.However,many foods do not require high temperature to conduct the Maillard reaction.For instance,Maillard reaction exists in the whole maturation process of fermented meat and plays a crucial role in the formation of its flavors.Currently,investigations on the reaction rules and mechanisms of mild Maillard reaction are insufficient,Therefore,it is necessary to explore the Maillard reaction of free amino acids in fermented meat products under mild conditions.In this study,three amino acids,arginine,alanine and lysine,with glucose were used as substrates for a single reaction system to establish three independent Maillard reaction systems:arginine-glucose,alanine-glucose and lysine-glucose to investigate the impact of reaction time and temperature on volatile flavor substances,substrate concentration,intermediate product changes as well as to determine the Maillard reaction rule of three amino acid-glucose systems under mild conditions.Furthermore,a Maillard reaction system of glucose with one of the three amino acids absent(absent arginine,absent alanine,absent lysine)was constructed,and through monitoring the intermediates and volatile product changes to verify independent single reaction system,hence to provide a theoretical basis for the Maillard reaction mechanism and reaction law of three amino acids in fermented meat products under mild conditions.The key research findings are as follows:(1)In arginine-glucose reaction system,the volatile compounds increased with the increase of temperature under mild conditions,among which the variety and content of esters and hydrocarbons were the most,followed by the alcohol compounds.By the comparison with the volatile products in arginine absent system,results indicated that the main volatile products generated by arginine were hydrocarbons and aldehydes,mainly including hexanal,valeraldehyde and o-xylene,etc.In addition,through observing the change of substrate concentration,It was found that the glucose concentration changed regularly with time and temperature,which mainly followed the Boltzmann equation,while the arginine concentration indicated a decreasing trend with the increasing of reaction time and temperature,the reduction rate reached to the peak at 40℃.The quantity of intermediate products in the initial stage of arginine system was greater than that in the middle stage.The content of intermediate products in the two stages both showed an increasing trend with prolonged time and rising temperature,and these changes followed zero-order kinetics.(2)The alanine reaction system under mild conditions indicated that the yield of volatile products and intermediates and consumption of substrates were small in the early phase,the reaction rate increased slightly under 40℃ till the later stage of reaction.The variety of volatile compounds produced in this reaction system were similar to the arginine system,mainly consist of ester and hydrocarbon compounds,followed by alcohol compounds.Comparing with the volatile products in the alanine absent system,it was found that the volatile compounds produced by the alanine system were mainly hydrocarbon compounds such as meta-xylene and p-xylene etc.The intermediates in this system were produced more in the initial stage of the reaction and changed most significant at 40℃,and it met the zero-order kinetics.The intermediate products in the intermediate stage showed an increasing trend with increasing temperature and time,but did not follow the zero-order kinetics.Through the detection of substrate concentration,results showed that with the increase of temperature and time,changes in the glucose concentration were not significant,basically following the Boltzmann equation.The decrease in alanine concentration mainly occurred mainly at the initial stage of the reaction(<10 days),and variation was most significant at 40℃.(3)The lysine reaction system had the highest degree of reaction among the three systems,and volatile products obtained in this system increased significantly with the rising temperature.Compared with the lysine absent system,the volatile compound produced by lysine were mainly consist of ketone compounds such as 2,3-butanedione,3-hydroxy-2-butanone or 2-butanone.The yield of the intermediate product was significant in the initial stage of the reaction.The formation rate of the intermediate product performed an evolution of fast increasing,midterm decrease and final stabilizing.The changes in both the initial and middle stages did not follow the zero-order kinetics.The consumption of glucose in the lysine system was much higher than the consumption of amino acid under the same reaction time and temperature conditions.The relationship between the glucose concentration consumption and reaction time followed the Boltzmann equation.In addition,the changes in amino acids were less obvious and unstable.(4)The Maillard reaction occurred in all three amino acid-glucose system under mild conditions.The reaction environment of the three amino acid systems was acidic,and the volatile products increased with rising temperature.Volatile products from the three different systems can be properly distinguished by principal component analysis method.The changes of glucose concentration over reaction time and temperature followed the Boltzmann equation.The zero-order kinetics was not applied to all amino acids.The degree of reaction of three amino acids was ranked in order from largest to smallest as following:lysine>arginine>alanine.