Food Waste Valorization Through Fermentation: Effects of Substrate Consistency, Acidification, and Sampling on Value-Added Compounds Production

Food waste management through fermentation offers a promising strategy for addressing the challenges of urban organic waste. This study explored the effects of substrate consistency (20% and 80%), based liquid type (mineral water, pH 8, and citric acid solution, pH 4), and sampling methods (destructive and non-destructive) on the production of value-added compounds during fermentation. Artificial food waste, modelled on Brazilian consumption patterns, was characterized for its physicochemical properties and fermented in non-agitated, bioreactors inoculated with a commercial microbial consortium. Rapid sugar consumption within 24–48 h resulted in lactic acid concentrations of 9.9 ± 1.0 g/L at 80% consistency and 4.4 ± 0.7 g/L at 20% consistency, corresponding to a 130% increase despite a fourfold rise in substrate loading, indicating non-proportional gains at higher consistency. High solids reactors with only spring water revealed lower lactic acid production (7.5 ± 1.0 g/L) and a pronounced shift towards butyric acid production after 7 days of fermentation, reaching 14.1 ± 3.0 g/L at the end of the process. Acidification also resulted in more stable acetic acid concentrations and increased ethanol production. These findings underscore the critical role of consistency, initial acidification, and sampling techniques in optimizing stable fermentations for organic waste valorization.