Enzymatic hydrolysis of chestnut puree:: Process optimization using mixtures of α-amylase and glucoamylase

The enzymatic hydrolysis of starch present in chestnut puree was performed through a one-step treatment with a mixture of a commercial thermostable a-amylase (Termamyl 120L, type S) and glucoamylase (AMG 300L) at 70 degreesC. The effect of the enzyme concentration and the ratio of both amylases in the reaction mixture was studied by means of a factorial second-order rotatable design, which allowed conditions to be set leading to the total conversion of starch to glucose after 15 min of incubation (60 total enzymatic units g(-1) of chestnut; ratio of alpha-amylase/glucoamylase enzymatic units, 0.35:0.65). At lower enzyme concentration, the delay in the addition of the glucoamylase with regard to the addition of the alpha-amylase allowed a slightly higher hydrolysis percentage to be reached when compared to the simultaneous addition of both amylases at the same low enzyme concentration. The kinetics of liberation of glucose supports the existence of a synergistic effect between these two enzymes only in the first moments of the reaction. Finally, a sequential one-step hydrolysis was assayed, and more concentrated glucose syrups were thus obtained.