Harnessing Waste Bread: From Potential Use in Microbial Growth and Enzyme Production to Techno-economic Assessment

Waste bread (WB) represents a valuable renewable resource for sustainable economic circular. Therefore, recycling WB is linked to food processing through fermentation, enzyme production, and sustainable food innovation. This study highlights WB as a major ingredient in growth medium for various microorganisms’ species and as a key factor in amylase production. Compared to conventional Luria-Bertani (LB) medium, the growth of the tested reference microorganisms (E. coli, E. faecalis, P. aeruginosa, and S. aureus) was improved by at least two-fold using 2% WB or (1/10 LB + 2%WB) reducing medium costs by up to 90%. Furthermore, it was confirmed that 1% WB can effectively replace starch during the screening of amylolytic strains. Applying a fractional factorial design, the production of amylase by Bacillus sp. BSS (Amy-BSS) was enhanced 15-fold. An analysis of the Pareto diagram revealed that WB was the most significant factor. Additionally, Amy-BSS was applied to hydrolyze polysaccharides in WB, enabling the generation of high-value-added products in food processing. This hydrolysis process yielded 4.6 g/L of fermentable sugars from 1% WB. Evaluating the economic feasibility of WB valorization into value-added products elucidates potential pathways for cost reduction and enhanced environmental sustainability, thereby positioning WB as a viable tool for sustainable development.