Kinetic modeling of fungal biomass growth and lactic acid production in Rhizopus oryzae fermentation by using grape stalk as a solid substrate.

This work proposes the use of grape stalk, a residue from the wine industry, as a solid substrate for R. oryzae NCIM 1299 fermentation to obtain lactic acid. The use of filamentous fungi on grape stalk as a fermentative solid substrate has not been studied yet making this study an innovative research work. Grape Stalk was chemically characterized, and according to its properties, it was deemed as an innovative material with great potential to be used as a fermentation substrate. R. oryzae growth kinetic determination needs the measurement of the biomass dry weight of fungus versus time, but the filamentous fungi penetration into the solid substrate makes the quantitative biomass removal from the substrate practically impossible. Therefore, fungal growth on membrane experiment was performed making gravimetric quantification of fungal biomass feasible. Two mediums were used comparatively, potato dextrose agar and a medium designed with agar and grape stalk for 5 days at 30 degrees C and 50%RH. Logistic, First Order and First Order Plus Dead Time models were used to model biomass growth, where these last two models have not been previously used for microbial kinetics studies. Growth kinetic parameters (X-max, mu(max), T-p and T-0) were found for all models and the First Order model showed the best fit with an R-2 equal to 91.84%. The Luedeking-Piret model was used to model lactic acid production and provided the parameters Y-p/x and m(p), with an R-2 equal to 90.05%. The kinetic parameters found here are also of great interest for further bioreactor designs.