Degradation kinetics of sugars (glucose and xylose), amino acids (proline and aspartic acid) and their binary mixtures in subcritical water: Effect of Maillard reaction.

• A kinetic framework was provided for biomass compounds released in subW. • Secondary char was formed by increasing T from sugar soluble degradation products. • Maillard reactions between sugars and amino acids in subW led to faster reaction loss. • Dehydration products formation was retarded in sugar + amino acid systems. • Higher relative reactivity in Maillard reactions was observed for xylose over glucose. A systematic kinetic study was conducted in subcritical water medium in the temperature range from 150 to 200 °C for pure glucose, xylose, proline and aspartic acid as well as binary mixtures of sugars + amino acids to understand the reaction kinetics and interactions among biomass components and to discern the influence of Maillard reaction (MR) on the overall reaction kinetics. The main degradation products identified for glucose and xylose were the respective dehydration products, hydroxymethyl furfural and furfural, yielding an increasing solid residue with temperature (15.9 wt% at 200 °C) with an augmented heating value. The degradation of sugars and amino acids in binary systems was faster compared to pure compounds due to MR and the production of dehydration products was delayed when considering total sugar conversion. Higher relative reactivity in MR was observed for xylose over glucose showing also higher antioxidant activity. [ABSTRACT FROM AUTHOR]