High-Yield and High-Titer Production of Levulinic Acid from Red Macroalgae via Sulfuric Acid-Catalyzed Hydrolysis:...

Levulinic acid (LA) is a versatile bio-based platform chemical with wide-ranging applications in biofuels, solvents, and biodegradable materials. To establish an efficient LA production strategy, red macroalgae were selected as the biomass feedstock due to their high carbohydrate content-particularly galactan, which is rich in 3,6-anhydro-L-galactose (AHG), a sugar that readily converts to LA under acidic conditions. In this study, a response surface methodology (RSM) based on a Box-Behnken design was used to optimize LA production from agar, the primary polysaccharide in red algae. The RSM model predicted an optimum of 172.5°C, 67.4 min, 8% H₂SO₄, with a predicted LA yield of 32.45%, and independent experimental validation under these conditions resulted in an LA yield of 33.23%. The validated reaction conditions were subsequently applied to two species of red macroalgae, Gracilaria verrucosa and Gelidium amansii. At 1% (w/v) biomass loading, carbohydrate-based LA yields of 52.9% and 48.4% were obtained, with corresponding titers of 3.1 and 3.0 g/L, respectively. Increasing the biomass loading to 25% (w/v) increased the LA titers to 49.8 and 48.6 g/L, while the corresponding carbohydrate-based yields decreased to 34.6% and 31.3%, respectively. These findings highlight the potential of high-solids processing as a practical approach for LA production from marine biomass and provide a basis for further process development toward sustainable biorefinery applications.