Efficient Formation Of Maillard Intermediates Dominated By Water Migration In Reaction Systems

The Amadori rearrangement product（ARP）or Heyns rearrangement product（HRP）formed in the initial stage of Maillard reaction is tasteless and non-volatile.ARP/HRP possess stable physicochemical properties during storage,but tend to degrade to complete the Maillard reaction and form fresh flavor compounds,which can realize the controlled formation of processed flavor and overcome the defects of unstable flavor enhancement effect of Maillard-type flavors during food cooking and processing.The controlled formation of thermal processing flavor of ARP is an important innovation direction for food flavor control technology.The Maillard reaction product of Aspartic acid（Asp）contains a large amount of flavor compounds including furans and ketones,which are important components of bakery aroma and sweet flavor,and the Asp-derived ARP has a promising application in bakery additives.In this paper,a method suitable for the large-scale and efficient preparation of Asp-Xyl-ARP was proposed,revealing the dynamic change law of moisture state under the dehydration effect and the mechanism of intermediate yield enhancement,clarifying the dependence of ARP yield on the water activity and moisture state of the reaction system,and studying the controlled formation law of flavor processing of aspartic acid Maillard reaction intermediate.The results can deepen the understanding of Maillard reaction theory and provide some theoretical basis for the industrial preparation of Maillard intermediate and its application as well as product development in flavor industry.The specific studies are as follows.The critical conditions for the aqueous preparation of aspartic acid-xylose ARP（Asp-Xyl-ARP）under atmospheric pressure were defined as p H 7.5,90℃,and 110 min.The yield of ARP in the aqueous phase was improved by rotary evaporation dehydration under vacuum condition.The prepared ARP was characterized by mass spectrometry and NMR spectroscopy after purification by ion exchange chromatography.The purified ARP was identified as N-1-deoxy-D-xylose-1-aspartic acid with two main isomers,and the relative molecular mass as well as molecular formula was determined to be 265 and C₉H₁₅NO₈,respectively.A high performance liquid chromatography（HPLC）method was developed for the seperation and determination of Asp-Xyl-ARP in aqueous phase using purified ARP as standard to achieve the quantitative analysis of ARP.The effect of the processing parameters on the moisture and ARP yield during the combined spray drying-vacuum drying dehydration process was investigated,and the following processing parameters were determined:the solids content of the stock solution for spray drying was 18.0%,and the addition of sodium chloride as a drying aid was 40%of the solids content of the stock solution;the inlet air temperature was 180℃,and the flow rate was 500 m L/h;the vacuum drying temperature and time were 90℃and 40 min,respectively.The conversion of ARP was increased from 1.68%to 26.53%by the high temperature transient dehydration of spray drying.By subsequent vacuum drying,the conversion of ARP was significantly increased to 77.92%.During the vacuum drying process,the water activity of vacuum dried products decreased from 0.185 to 0.114,and the percentage of bound water increased from 63.9%to88.4%,while the percentage of immobilized water also decreased significantly.This result indicated that the continuously dissipation of free water caused the conversion of immobilized water to free water with the prolongation of drying time in the process of vacuum dehydration,and according to the law of entropy increase,the decrease of immobilized water led to the tendency of conversion from bound water to immobilized water.The reduction of bound water in the system promoted the intramolecular dehydration of the Asp-Xyl system,which shifted the chemical equilibrium toward the formation of intermediates and facilitated the production of the ARP precursor substance,i.e.,imine,thus significantly increasing the yield of Asp-Xyl-ARP.The above findings suggest that water activity and water presence status can be used as the main indicators to reflect the degree of dehydration and effective formation of ARP.The formation ability of thermal processed flavor derived from Asp-Xyl-ARP was investigated.The flavor formation patterns of four systems,namely Asp-Xyl mixed solution,spray drying-vacuum drying product of ARP reaction solution,purified Asp-Xyl-ARP,and Asp-Xyl derived complete Maillard reaction product（MRPs）,were investigated under simulated baking conditions.The results showed that at the same amino molar concentration,the formation rate and quantity of flavor substances produced by the ARP and spray drying-vacuum drying product systems were much higher than those of MRPs and Asp-Xyl mixed solutions,and the types of flavor substances and the total amount of flavor produced by the spray drying-vacuum drying product system were higher than those of the purified ARP system.Therefore,the spray drying-vacuum drying products derived from Asp-Xyl system revealed superior advantages than purified ARPs and MRPs in terms of controlled flavor formation and can be applied in field of food flavor enhancement to obtain the desired fresh flavor.The application effect of Asp-Xyl-ARP in baking systems was investigated.Different proportions of spray drying-vacuum drying products were added to the finger cookie systems,and the volatile flavor substances,flavor profiles,color and taste of finger cookie samples were evaluated comprehensively by GC-MS,colorimetry and sensory evaluation.The results showed that the addition of Asp-Xyl derived spray drying-vacuum drying product in a proportion of0.3%showed the best flavor and color enhancement effect on the finger cookie system as well as the best sensory quality of finger cookies.