Application of ensilage as a green approach for simultaneous preservation and pretreatment of macroalgae Ulva lactuca for fermentable sugar production

Green macroalgae Ulva lactuca could be a potential marine biomass feedstock for the production of biofuel and biochemicals. However, the high moisture content makes long-term preservation of fresh Ulva biomass a challenge. Ensilage has been suggested as a green approach to preserving and pretreating fresh biomass without intensive energy input. In this study, silage additives including cellulase complex and inoculum of Lactobacillus plantarum were tested and applied to circumvent the difficulties associated with ensilage of the Ulva species, such as insufficient water-soluble carbohydrate and low lactic acid bacteria (LAB) count. The experimental results with statistical analysis indicated that the addition of both cellulase complex at 10 carboxymethyl cellulose unit (CMCU)/g dry biomass and inoculum of Lactobacillus plantarum at 10⁶ cfu/g dry biomass was necessary to drop silage pH value to lower than 4 in 15 days. The successful preparation of Ulva silage could retain around 92% solid and most of the carbohydrates and the ensiled Ulva biomass could produce more reducing sugar than fresh biomass by dilute acid hydrolysis at high solid content and moderate temperature. Moreover, with further enzymatic hydrolysis, the Ulva silage proved to be fermentable by LAB for lactic acid production. The results suggested that ensilage could be a useful process for simultaneous preservation and pretreatment of Ulva biomass for fermentable sugar production.