Enhancement of Growth and Paramylon Production of Euglena gracilis by Upcycling of Spent Tomato Byproduct as an Alternative Medium

Euglena gracilis (E. gracilis) accumulates paramylon, an immune-functional beta-glucan that can be used as a functional food. Paramylon production is strongly affected by the organic carbon source and the initial pH conditions. Food processing byproducts have attracted attention for microalgal cultivation because of their low cost and abundance of nutrients, including carbon and nitrogen. We investigated the optimal carbon source and its concentration for efficient paramylon production. A spent tomato byproduct (STB) generated from a tomato processing plant was applied for biomass and paramylon production from E. gracilis with respect to the initial pH condition. The highest paramylon concentration (1.2 g L−1) and content (58.2%) were observed with 15 g L−1 glucose. The biomass production increased when STB was used as compared with that when a synthetic medium was used (1.6-fold higher at pH 3 and 2-fold higher at pH 8). The optimal initial pH was determined according to the maximum production of biomass and paramylon. Upcycling the food processing byproduct, STB, can contribute not only to cost reduction of the biorefinery process using E. gracilis but also to environmental remediation by removing organic carbon and nitrogen from the byproducts.