Accelerated Dissipation of Free and Immobilized Water Facilitating the Intramolecular Dehydration of N-Xylosamine and Conversion Improvement of the Amadori Rearrangement Product of Aspartic Acid-Xylose Reaction

Compared to the method of aqueous Maillard reaction at atmospheric pressure tandem vacuum concentration, a coupling dehydration method combining spray drying and vacuum drying was used to increase aspartic acid-xylose conversion to the Amadori rearrangement product (ARP). The water activity and moisture states were found as effective indicators to characterize the degree of dehydration of Maillard reaction intermediates and efficient formation of ARP. During the vacuum drying process, the water activity of the product powder decreased significantly. Because the formation of ARP was accompanied by intramolecular dehydration, combining spray drying and vacuum drying increased the proportion of bound water in the vacuum-dried product. Free water was easily dissipated via dehydration, which then converted the immobilized water continuously to free water, and the decreased immobilized water further converted the bound water to immobilized water. The reduction in bound water contributed to the intramolecular dehydration of N-substituted d-xylosamine, which would further be transformed to be the ARP through an intramolecular rearrangement. The yield of ARP was increased from 1.68 to 21.53% after spray drying. The ARP yield was substantially increased up to 77.9% by subsequent vacuum drying.