Feasibility of improving carbohydrate content of Chlorella S4, a native isolate from the Persian Gulf using sequential statistical designs

Microalgal carbohydrates can serve as feedstock for bioethanol production. Environmental and/or nutritional factors influence the carbohydrate content of microalgae and optimization of culture condition has a key role in the economic production of bioethanol. This research has evaluated the optimization of the carbohydrate content of a marine microalga isolate from the Persian Gulf. The Plackett-Burman design was used to screen the most effective parameters responsible for carbohydrate production. Then, the levels of two effective factors, total phosphate (KH2PO4+K2HPO4) and initial pH, were optimized by two types of Response Surface Method designs (Central Composite and historical data designs). Maximum carbohydrate production was obtained at a low concentration of phosphate (0.031 g/L) and initial pH of 5.95. Under optimal condition, the concentration of carbohydrate was increased by 1.9 folds, from 0.12 g/L (0.2 g/g of dry biomass) to 0.230 g/L (0.365 g/g of dry biomass). The carbohydrate content of microalga hydrolysate was also evaluated by the HPLC method, and the results showed that glucose made about 3.19% (w/w) of total carbohydrates. This study represents the isolation and determination of a promising native and non-invasive microalga for bioethanol production, and subsequently enhancement of its carbohydrate content for the same goal.