Production of raw starch degrading enzyme by the thermophilic filamentous bacterium Laceyella sacchari LP175 and its application for ethanol production from dried cassava chips

Physical factors that enhanced the production of raw starch degrading enzyme by a thermophilic filamentous bacterium, Laceyella sacchari LP175 in a 3 L airlift fermenter, were optimized at a pH of 6.5, a temperature of 45°C, and an aeration rate of 0.5 vvm using a central composite design. This yielded 278 U/mL, at 36 h cultivation, an increase in enzyme production and productivity of 1.53‐ and 2.04‐fold, respectively, as compared with a shaking flask cultivation. Raw starch degrading enzyme produced by L. sacchari LP175 with commercial glucoamylase synergistically enhanced the hydrolysis of 300 g/L dried cassava chips (71% starch content) to 157 g/L reducing sugars, equivalent to 66.3% hydrolysis at pH 6.5 and 50°C for 12 h. The comparative study on bioethanol production in a non‐sterile system from dried cassava chip by three different processes; the maximum production, 90.9 g/L (88% theoretical yield), was obtained by modified simultaneous saccharification and fermentation at 50°C for 6 h and subsequent fermentation by the thermotolerant Kluyveromyces marxianus DMKU‐KS07 at 42°C within 18 h with the highest productivity of 3.79 g/L/h. The other processes tested – separate hydrolysis and fermentation and simultaneous saccharification and fermentation – yielded 83 and 51.6 g/L of ethanol, respectively.