Optimization of solid-state enzymatic hydrolysis of chestnut using mixtures of α-amylase and glucoamylase

Solid-state hydrolysis of starch present in chestnut was assayed in a single step with a mixture of a thermostable alpha-amylase and glucoamylase at three temperatures: 17 and 30degreesC, for simultaneous hydrolysis and ethanol fermentation, and 70degreesC, the optimal temperature for these enzymes. Total hydrolysis was only reached at the highest temperature, leading to a more concentrated hydrolysate than in submerged hydrolysis. Mass transfer limitations and starch retrogradation appear as the main causes for the incomplete hydrolysis of chestnut starch in solid-state operation at 17 and 30degreesC. Even accepting that this limitation causes a 15% reduction of the yield of the hydrolysis with respect to the submerged process or the solid process at high temperature, solid-state hydrolysis at low temperatures seems to be adequate for simultaneous solid-state hydrolysis and fermentation processes.