Effects of temperature and neutralizing agent on lactic acid production by Rhizopus sp. fermentation

Lactic acid is a raw material for Poly Lactic Acid (PLA) as a biodegradable polymer. One of the lignocellulosic biomass which has the potential as a feedstock to produce lactic acid is sugar palm starch waste (SPSW). This study purposes to investigate the effects of temperature and neutralizing agent on lactic acid production. SPSW has high cellulose content (40.10%) and lignin (27.24%). The presence of lignin content can inhibit the process of cellulose hydrolysis into reducing sugar. Therefore, the pretreatment process is necessary to remove lignin—the acid-organosolv pretreatment using H2SO4 0.2 M and 30% ethanol with 3% NaOH as a catalyst can reduce lignin content to 27%. Subsequently, The hydrolysis process using the cellulase enzyme from Trichoderma reseei for 24 h at 60 °C and 125 rpm. The concentration of reducing sugar (5.3144 g/L) was analyzed using the DNS method. Afterward, the aerobic fermentation process has carried out using Rhizopus oryzae and Rhizopus arrhizus with various temperatures (30, 34, 38, and 42 °C) and CaCO3 concentrations as neutralizing agents (0.6 and 0.8 (w/v)). The highest lactic acid concentration was obtained after incubation during 48 h at 30 °C; 150 rpm with CaCO3 concentration 0.8 g/L is 2.1751 g/L for Rhizopus oryzae and 2.7062 g/L for Rhizopus arrhizus.