Production and characterization of raw starch degrading enzyme from a newly isolated thermophilic filamentous bacterium, Laceyella sacchari LP175

Medium optimization for production of raw starch degrading enzyme (RSDE) from a newly isolated thermophilic filamentous bacterium, Laceyella sacchari LP175, is described. Yeast extract and raw cassava starch were found to be the best nitrogen and carbon sources, respectively, for enzyme production. Response surface methodology with Plackett–Burman design and central composite design showed that an optimized concentration of 4.93 g/L raw cassava starch and 2.8 g/L yeast extract in basal medium yielded 181.1 U/mL RSDE activity in a shaking flask at 50°C and pH 7.0 after 48 h. Maximum RDSE activity in crude enzyme was achieved at pH 6.5 and 50°C. The major end product of raw cassava starch hydrolysis was maltose (88%). The Km and Ki values of raw cassava starch and maltose, respectively, were found to be 2.85 mg/mL and 1.04 mg/mL. Raw cassava starch at 100 g/L was hydrolyzed with 200 U/mL RSDE for 12 h, yielding 36.8% hydrolysis. The addition of commercial glucoamylase (1.6 U/mL) synergistically enhanced the hydrolysis reaction, yielding 70% hydrolysis (equivalent to 78.0 g/L glucose). The high efficiency of RSDE produced from L. sacchari LP175 could be useful for replacing conventional enzymes currently used in various raw starch processing industries.