Lactic Acid Production from Acid Hydrolysate of Ulva pertusa as a Sustainable Biomass Feedstock

The development of sustainable alternatives to fossil-based feedstocks is a global priority in light of climate change and resource depletion. Seaweeds, particularly green seaweeds, represent promising candidates for biorefinery applications due to their rapid growth, high carbohydrate content, and non-competition with arable land. In this study, the feasibility of lactic acid production from acid hydrolysates of the green seaweed Ulva pertusa was systematically investigated. Proximate composition analysis revealed that dried Ulva pertusa contained 52.3% carbohydrates, highlighting its suitability as a fermentation substrate. Acid hydrolysis with dilute sulfuric acid released 23.8 g of fermentable monosaccharides per 100 g of biomass, with L-rhamnose and D-glucose as the predominant sugars. Fermentation experiments were conducted using five Lactobacillus strains (L. casei, L. plantarum, L. brevis, L. salivarius, and L. rhamnosus). Among these, L. rhamnosus and L. salivarius achieved the highest lactic acid yields (0.66 g g^-1), followed by L. plantarum (0.63 g g^-1), whereas L. casei and L. brevis exhibited comparatively lower yields (0.46 and 0.39 g g^-1, respectively). Time-course analysis demonstrated that the superior strains reached maximum productivity within 9 h, significantly faster than typical lignocellulosic feedstocks such as corn stover, which require extensive pretreatment and longer fermentation times. Furthermore, the mineral-rich composition of Ulva pertusa (notably Mg²⁺ and Ca²⁺) provided intrinsic nutrients that supported microbial growth, thereby reducing the requirement for external supplementation. Comparative evaluation with lignocellulosic hydrolysates confirmed that Ulva pertusa offers higher efficiency, faster kinetics, and lower process complexity. To our knowledge, this work represents the first comprehensive assessment of multiple Lactobacillus strains for lactic acid production from Ulva pertusa hydrolysates. The findings highlight the unique advantages of green seaweeds as a sustainable biomass resource and contribute to the advancement of marine biomass-based biorefineries. Future studies should focus on improving the utilization of non-fermentable sugars, optimizing fermentation strategies, and evaluating techno-economic feasibility on an industrial scale.