Behaviors of glucose decomposition during acid-catalyzed hydrothermal hydrolysis of pretreated Gelidium amansii

► Decomposition behaviors were investigated during acid-catalyzed hydrothermal hydrolysis. ► Experiments were conducted with four different acid catalysts at various acid normalities. ► Operating condition for maximizing glucose yield was established, but requires new strategies. ► Glucose decomposition behavior suggested that considerable attention should be directed at the production of levulinic acid. ► Levulinic acid has a potential as a platform chemical.