Effect of milling and enzymatic hydrolysis in the production of glucose from starch-rich Chlorella sorokiniana biomass

Starch-accumulating microalgae are a potential source of glucose, a valuable industrial feedstock. However, the recalcitrance of their cell wall hinders the enzymatic hydrolysis of the intracellular starch. This work studied starch accumulation, cell wall disruption, and enzymatic hydrolysis of the green microalga Chlorella sorokiniana. Starch accumulation reached 26% of the microalgal biomass in response to nitrogen starvation. The use of cellulases for cell wall disruption was not successful; however, disruption of the dry biomass using a vibratory mill was very effective for the hydrolysis of the intracellular starch by amylases. In reaction mixtures with a solids loading of 5% (m/m), the starch of milled cells was hydrolyzed by fungal amylases, without a prior gelatinization step, to a final respective glucose yield and concentration of 99% and 16 g.L-1 within 5 h. The increase of the solids loading to 25% (m/m) resulted in a glucose yield and concentration of 75% and 70 g.L-1, respectively, within the same reaction time.