Peptide Rich Fermentates from Surplus Bread: Screening for ACE/α Glucosidase Inhibition, Antioxidant Capacity and Antimicrobial Activity

Abstract

This study evaluates the valorization of surplus bread as a substrate for microbial production of bioactive peptides with antidiabetic, antioxidant, and antimicrobial properties. Surplus bread was enzymatically hydrolyzed (alcalase, α‐amylase, amyloglucosidase) and fermented with a collection of 35 isolates (20 yeasts, 15 lactic acid bacteria) obtained from sourdough, lyophilized sourdough, kefir and commercial probiotics. Fermentates were characterized for peptide content (α‐amino nitrogen), enzyme inhibition (ACE, α‐glucosidase), antioxidant capacity (DPPH, FRAP) and bacteriostatic activity (agar well diffusion against S. aureus and E. coli). ANOVA indicated a significant effect of strain on peptide release (R2 = 87.7%, adj. R2 = 76.2%), and strain and peptide concentration significantly influenced antioxidant assays (DPPH R2 ≈ 97.6%, FRAP R2 ≈ 92.6%). Fermentation increased peptide levels 1.5–4.8‐fold relative to hydrolysates. Several LAB ( L1, L2, L11, L12) consistently produced 60–70% ACE and α‐glucosidase inhibition, while several yeast isolates (Y11, Y19, Y20) achieved the highest ACE inhibition (up to >90%). Antioxidant capacity reached ~40–48% in top-performing strains. Antimicrobial assays revealed clear inhibition halos against S. aureus for specific LAB (L1, L3, L11, L13) but no activity against E. coli, indicating selective Gram‐positive antagonism. These results demonstrate that surplus bread can be converted into multifunctional peptide-rich fermentates with potent antidiabetic and antioxidant effects and targeted antimicrobial activity. The work establishes a strain repository and supports further proteomic and structural characterization to optimize peptide yields and bioactivity. Valorization of surplus bread aligns with circular bioeconomy and SDG objectives by reducing food waste while generating value‐added functional ingredients with translational potential