Abstract
Different agro-industrial residues and bioproducts were studied, such as sugar cane juice, molasses, cheese whey and cassava wastewater as carbon source and autolysate, yeast, yeast extract, corn steep liquor (CSL), pro-floo (protein seed cotton), as well as ammonium sulfate as nitrogen sources. The fermentations were carried out in bioreactor with six glasses vases of 1.5 L and the initial pH was controlled to 6.2 using 10 M NaOH at 37 °C and 200 rpm. The best agro-industrial substrates for lactic acid production were cheese whey as carbon source and corn steep liquor as nitrogen source. A central composite design (CCD) was employed to determine maximum lactic acid production at optimum values for the variables, lactose (X1) and CSL (X2). Statistical analysis of the results showed that the linear terms of these two variables had significant effects as well as the quadratic term of lactose (X12). A second-order polynomial regression model estimated that the maximum lactic acid concentration of 114.73 g/L was obtained when the optimum values of lactose and CSL were 143 g/L and 60 mL/L, respectively, after 48 h of fermentation. Verification of the optimization showed that L(+)-lactic acid concentration was of 116.5 g/L. During the fermentation, the concentration of lactose decreased from 143 g/L to 1.4 g/L at the end of cultivation and the growth. The higher productivity (3.45 g/Lh) was obtained after 24 hours of fermentation.
Keywords: cheese whey, cassava wastewater, molasses, sugar cane juice, corn steep liquor; Lactobacillus rhamnosus; L(+)-Lactic acid.