Hydrolysis of ginger bagasse starch in subcritical water and carbon dioxide.

Ginger bagasse from supercritical extraction was hydrolyzed using subcritical water and CO(2) to produce reducing sugars and other low molecular mass substances. Response surface methodology was used to find the best hydrolysis conditions; the degree of hydrolysis and the yield were the two response variables selected for maximization. The kinetic studies of the hydrolysis were performed at 150 bar and temperatures of 176, 188, and 200 degrees C. The higher degree of hydrolysis (97.1% after 15 min of reaction) and higher reducing sugars yield (18.1% after 11 min of reaction) were established for the higher process temperature (200 degrees C). Different mixtures of oligosaccharides with different molecular mass distributions were obtained, depending on the temperature and on the reaction time. The ginger bagasse hydrolysis was treated as a heterogeneous reaction with a first-order global chemical kinetic, in relation to the starch concentration, which resulted in an activation energy of 180.2 kJ/mol and a preexponential factor of 5.79 x 10(17)/s.