Reduction of phenolics in faba bean meal using recombinantly produced and purified Bacillus ligniniphilus catechol 2,3-dioxygenase

Abstract

Abstract Pulse meal should be a valuable product in the animal feed industry based on its strong nutritional and protein profiles. However, pulse meal contains anti-nutritional and anti-palatability compounds, including (poly)phenolics (tannic and non-tannic), such that improvements in pulse meal processing are still needed to increase its uptake by the industry. Microbial fermentation is currently used as a strategy to decrease tannin content, but results in the undesirable accumulation of monophenolics. Here we investigate the viability of cell-free biocatalytic reduction of phenolic content in faba bean (Vicia faba) meal. A representative catechol dioxygenase, Bacillus ligniniphilus L1 catechol 2,3-dioxygenase (BLC23O) was used in this proof-of concept based on its known stability and broad substrate specificity. Its amenability to large scale recombinant production was established, and its ongoing stability in complex environments including resuspension in slurries of faba bean meal demonstrated. Reaction results suggest that BLC23O is effective for biocatalytic phenol reduction in faba bean meal. However, the upstream hydrolytic release of phenolics from higher molecular weight species (tannins, proteins, carbohydrates) likely remains a rate limiting step, in the absence of other enzymes or microbial fermentation. Overall, this study highlights the potential viability of the biocatalytic processing of pulse meals, for optimization of their nutritional and economical value in the animal feed industry.