Optimization of bioprocesses with Brewers’ spent grain and Cellulomonas uda

Abstract

Brewers' spent grain (BSG) is a low-value by-product of the brewing process, which is produced in large quantities every year. In this study, the lignocellulosic feedstock (solid BSG) was used to optimize fermentations with Cellulomonas uda. Under aerobic conditions, maximum cellulase activities of 0.98 nkat•mL −1 , maximum xylanase activities of 5.00 nkat•mL −1 and cell yields of 0.22 g Cells •g BSG −1 were achieved. Under anaerobic conditions, enzyme activities and cell yields were lower, but valuable liquid products (organic acids, ethanol) were produced with a yield of 0.41 g Prod •g BSG −1 . The growth phase of the organisms was monitored by measuring extracellular concentrations of two fluorophores pyridoxin (aerobic) and tryptophan (anaerobic) and by cell count. By combining reductive with anaerobic conditions, the ratio of ethanol to acetate was increased from 1.08 to 1.59 mol EtOH •mol Ac −1 . This ratio was further improved to 9.2 mol EtOH •mol Ac −1 by lowering the pH from 7.4 to 5.0 without decreasing the final ethanol concentration. A fermentation in a bioreactor with 15 w% BSG instead of 5 w% BSG quadrupled the acetate concentration, whilst ethanol was removed by gas stripping. This study provides various ideas for optimizing and monitoring fermentations with solid substrates, which can support feasibility and incorporation into holistic biorefining approaches in the future.

Valorisation of Brewer’s Spent Grain: Lignocellulosic Fractionation and its Potential for Polymer and Composite Material Applications

“…The ethanol to acetate ratio could be increased significantly by adapting the pH. [101] The overview of all building blocks obtainable from BSG's lignocellulosic biomass (LCB) according to the literature so far are displayed in Promising examples of BSG biomass fractionation have been described, showing the potential of such an application for high valorisation strategies. However, challenges are still to be overcome for an optimal valorisation such as efficient scale-up and biorefinery designing, to assess the feasibility of complete valorisation of this bioresource, its economic viability and environmental impact.…”

Xylanase Production by Cellulomonas phragmiteti Using Lignocellulosic Waste Materials

“…These results prove that the most dominant enzyme, in terms of activity, in the extracellular extracts of C. phragmiteti is xylanase, and other lignocellulolytic enzyme activities are also present. [14,15,38]. These authors related this activity to the large amount of xylanases secreted by the bacteria under appropriate culture conditions.…”

Fungal‐Based Biorefinery: From Renewable Resources to Organic Acids

“…Several attempts have been made to produce organic acids using raw material as substrate by either bacteria or fungi. Akerman et al reported the production of acetic acid by Cellulomonas uda using brewers' spent grain as feedstock [14]. Lactic acid was produced by Lactobacillus spp.…”

“…Akerman et al. reported the production of acetic acid by Cellulomonas uda using brewers' spent grain as feedstock 14. Lactic acid was produced by Lactobacillus spp.…”