Journal
BIOCHEMICAL ENGINEERING JOURNAL
Volume 169, Issue -, Pages -Publisher
ELSEVIER
DOI: 10.1016/j.bej.2021.107959
Keywords
Neurospora intermedia; Semi-continuous bioreactor; Plug flow bioreactor; Solid-state fermentation; Bread waste
Funding
- Swedish Agency for Economic and Regional Growth via European Union European Regional Development Fund within the project 'Ways2Taste'
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Stale bread, a major food waste, was successfully converted into new food products through solid-state fermentation using a plug-flow bioreactor, showing improved productivity compared to batch fermentation. By adjusting residence time and inoculum-to-substrate ratio, the fermentation performance could be effectively controlled, leading to reduced starch content in the substrate.
Stale bread, one of the major food wastes, holds great potential to produce new food products by solid-state fermentation using the edible filamentous fungus Neurospora intermedia. Yet, this process is limited to small-scale batch production. In this study, a plug-flow bioreactor was developed and successfully operated semicontinuously without addition of external inoculum. Two critical process parameters namely residence time and inoculum-to-substrate ratio (ISR) were studied in two experimental set-ups, 48 h and ISR 10:65 or 24 h and 20:55. The fermentation performance was assessed by the CO2 evolution rate and starch degradation in the substrate. Both experiments resulted in a relatively stable CO2 evolution rate up to 10 days and the starch content was reduced from 65 % in bread to 40.6 % and 43.2 %, respectively, in the product. Performance of the plug-flow bioreactor was compared to batch fermentation in tray bioreactors using the same ratio of inoculum. No significant differences of the final starch content were observed between the bioreactors, which indicate improved productivity by the semi-continuous process compared to the batch. The fungal biomass yield was calculated to range from 0.12 to 0.5 mol C-biomass/mole C-substrate . A material balance of the process revealed that 220 g dry bread and 200 ml water were required to produce 400 g fermented product with a fungal biomass content of 15 % in 24 h.
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