Dynamic Optimization of Lactic Acid Production from Grape Stalk Solid-State Fermentation with Rhizopus oryzae Applying a Variable Temperature Profile

Abstract

Lactic acid is widely used in the food industry. It can be produced via chemical synthesisor biotechnological pathways by using renewable resources as substrates. The main challengeof sustainable production lies in reaching productivities and yields that allow for their industrialproduction. In this case, the application of process engineering becomes a crucial tool to improve theperformance of bioprocesses. In this work, we performed the solid-state fermentation of grape stalkusing Rhizopus oryzae NCIM 1299 to obtain lactic acid, employing three different temperatures (22,35, and 40 ◦C) and a relative humidity of 50%. The Logistic and First-Order Plus Dead Time modelswere adjusted for fungal biomass growth, and the Luedeking and Piret with Delay Time model wasused for lactic acid production, obtaining higher R2 values in all cases. At 40 ◦C, it was observed thatRhizopus oryzae grew in pellet form, resulting in an increase in lactic acid productivity. In this context,the effect of temperature on the kinetic parameters was evaluated with a polynomial correlation.Finally, using this correlation, a smooth and continuous optimal temperature profile was obtained bya dynamic optimization method, improving the final lactic acid concentration by 53%.