Potential of sugar beet vinasse as a fermentation feedstock for industrial enzyme production

Vinasse is a waste stream from industrial bioethanol production following distillation. It is derived from either sugar cane or sugar beet and contains substantial quantities of glycerol, other C5-C6 sugars, proteins and minerals that can be potentially exploited as culture medium. Here we demonstrate the feasibility of using sugar beet vinasse as a fermentation feedstock for industrial enzyme production within an integrated biorefinery. We focus on transaminase (TAm) which we are also investigating for chiral amine production from sugar beet pulp feedstocks. The effect of vinasse concentration (17, 25, 50 and 100% v/v) and IPTG induction on E. coli growth and TAm expression were assessed in a parallel 24-well miniature bioreactor system (6.5 mL). Our results showed that comparable cell growth profiles were observed in fermentations using raw vinasse up to 25% (v/v) while increasing the concentration has an inhibitory effect on cell growth. Assessment of IPTG induction demonstrated that TAm was efficiently expressed in non-induced cultures due to autoinduction by galactose present in vinasse. A maximum TAm specific activity of 118.2 U g_dcw^-1 was attained in non-induced fermentation using 25% (v/v) raw vinasse which was comparable with that achieved in complex medium. The result obtained in the miniature bioreactors were found to be reproducible at laboratory scale. Overall, the findings presented here emphasise the potential of sugar beet vinasse as feedstock for economical production of industrial biocatalysts.