Study of the effects of temperature and pH on lactic acid production from fresh cassava roots in tofu liquid waste by Streptococcus bovis

Abstract

We report a study of the effects of temperature and pH on the kinetics of lactic acid production from fresh cassava roots (FCR) by Streptococcus bovis in new media: tofu liquid waste (TLW); TLW with 2 wt% concentrated maguro waste (TLW + CMW2); and in a standard trypto-soya broth (TSB) compared with a standard medium (glucose in TSB). The results showed that 39 °C and pH 5.5 were optimal for fermentation properties (lactic acid concentration, productivity and specific growth rate) in all media, including the standard. The energy of activation ( E a) and the energy of deactivation ( E d) of lactic acid fermentation in all media were calculated using the Arrhenius relation. The E a and E d values increased in the order FCR in TLW < FCR in TLW + CMW2 < glucose in TSB < FCR in TSB, while values of productivity and specific growth rate decreased in the same order. The effects of pH on productivity and specific growth rate were evaluated by Michaelis–Menten and Monod-type equations. For pH, the inhibition is competitive for both productivity and specific growth rate. By controlling the pH at 5.80, the inhibition for both productivity and specific growth rate were minimized in all media.