<i>L</i>(+)‐Lactic acid from sweet sorghum by submerged and solid‐state fermentations

Abstract

Abstract Sweet sorghum was used as the raw material for the lactate production by a strain of Lactobacillus paracasei . The submerged conversion of sugar juice obtained from sweet sorghum by extraction could be accomplished with the same efficiency as observed in a control experiment with MRS‐glucose medium (final lactate concentration of 88–106 g/l, lactate yield of 91–95%, duration of the fermentation of 24–32 h). Finely ground stalks of sorghum served as the substrate in the solid‐state fermentation. The lactate accumulation in the solid medium and the lactate yield were optimized up to values comparable with the results from the submerged fermentation (final lactate concentration of 90 g/kg, lactate yield of 91–95%). However, the duration of the fermentation amounted to 120–200 h in the solid‐state process. The data from a series of experiments performed at variable values of temperatures between 30°C and 36°C and initial sugar concentrations between 60 g/kg and 115 g/kg, and degrees of moisture between 78% and 82% was the basis of a polynomial multidimensional regression. As a result, simple three‐dimensional model functions were obtained for the maximum productivity of lactate formation, the lactate yield and the time required for a 90% conversion.