Optimization of operating variables for polyphenol extraction from lipid-extracted microalgae using acid-catalyzed hot-water extraction

Microalgae are a promising source of lipids for biodiesel production, which has the potential to replace fossil fuels without affecting the supply of foods and crop products. From the production of biodiesel, a solid waste known as lipid-extracted microalgae (LEM) is generated as a byproduct, and it is considered a rich source of antioxidant compounds, mainly polyphenols. In this study, optimization of the process variables of acid-catalyzed hot-water extraction was performed at low temperature in order to increase the production of polyphenols from LEM (Tetraselmis KCTC 12236BP). A statistically based method was used to optimize key variables, including extraction temperature, time, and sulfuric acid concentration. The results indicated that all process variables had significant effects on the extraction of polyphenols (p < 0.05). For instance, polyphenol levels increased in accordance with the increase of the three variables. The most economical optimal conditions were 100°C, 46.8 min, and 0.32 N H₂SO₄, under which polyphenol yield was 8.04 mg gallic acid equivalent (GAE)/g dry matter (DM), 5.2-fold higher than that from hot-water extraction without optimization.