Abstract
Microalgae are considered as sustainable starch producers, yet the carbon sources for this process in terms of starch productivity and functionality require further elucidation. The present study investigated the roles of CO(2) and acetate on the starch production in a marine microalga Tetraselmis subcordiformis, and the ordered structure and digestibility of the starches obtained were characterized. CO(2) and acetate could serve as efficient carbon sources for T. subcordiformis to accumulate starch, with the maximum starch content, yield, and productivity reaching 66.0%, 2.16 g/L, and 0.71 g/L/day on day 3 and the maximum biomass productivity reaching 0.94 g/L/day on day 2, respectively, when 2.5 g/L sodium acetate and 2% CO(2) were simultaneously applied. The addition of acetate under 2% CO(2) improved the photosynthetic efficiency and enhanced the activity of ADP-glucose pyrophosphorylase, facilitating the biomass and starch production. The supply of CO(2) and acetate changed the amylose/amylopectin ratio by affecting the activity of starch branching enzymes and isoamylases. FTIR and XRD analyzes showed that the supply of CO(2) reduced the long- and short-range ordered structure of starch, while acetate promoted the production of additional B- and V-type starch, resulting in a reduced digestibility. The combined supply of 2% CO(2) and 5 g/L sodium acetate enabled the most efficient production of functional resistant starch (RS) measured with Englyst's method, with a maximum RS content and yield reaching 13.7%DW and 0.40 g/L, respectively, on day 3. This study provided novel insights into the efficient production of high value-added functional starch (RS) from microalgae.