Optimization of hydrolysis conditions for the production of glucomanno-oligosaccharides from konjac using β-mannanase by response surface methodology

► The change in the direct reducing sugar (DRS) is consistent with total reducing sugar (TRS) but contrary to the degree of polymerization (DP). ► DRS could be used as an indicator of the content of GMO in the RSM study. ► The optimum RSM operating conditions were: reaction time of 3.4 h, reaction temperature of 41.0 °C, pH of 7.1 and enzyme to substrate ratio (E/S) of 0.49. ► The enzymatic hydrolysis was enhanced by temperature, pH and incubation time.