Valorization of low-grade <i>Gracilaria verrucosa</i> biomass via optimized acid hydrolysis: a sustainable route to high-value sugars for bioproduct development

Low-grade <i>Gracilaria verrucosa</i> biomass, typically discarded during seaweed processing, remains underutilized despite its rich polysaccharide content. This study explores the valorization of this waste stream through optimized acid hydrolysis, comparing conventional water bath heating and pressurized steam pretreatment. A low-concentration sulfuric acid (H₂SO₄) hydrolysis process was statistically optimized using response surface methodology (RSM), employing a central composite design (CCD), yielding a maximum reducing sugar concentration of 56.54 g/L under pressurized steam conditions-substantially higher than 37.51 g/L under water bath treatment. Structural changes in the biomass were characterized via scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and density measurements, revealing enhanced polysaccharide breakdown under pressurized conditions. Importantly, the sugar-rich hydrolysate, dominated by glucose and xylose, demonstrates potential as a substrate for microbial fermentation, supporting downstream bioproduct development such as biodegradable plastics. These findings offer a sustainable pathway for converting seaweed processing waste into high-value biochemical feedstocks using a mild, cost-effective hydrolysis process.