A comprehensive study on non-enzymatic browning in cowpea pickles during storage based on a model system.

Non-enzymatic browning during storage devalues pickled vegetables, yet roles of the Maillard reaction (MR), ascorbic acid (AA) degradation, sugar degradation and phenolic oxidation are unclear. Fourteen defined model systems (M1-M14) mimicking cowpea pickles composition were incubated at 45 °C for 40 d. Browning index and reactants, intermediates, and products were tracked. Pronounced visible browning and BI increases were mainly observed when amino acids and sugars coexisted (M3-M14), whereas amino acids (M1) or sugars (M2) alone showed limited discoloration. AA was nearly depleted by day 20 and 3-hydroxy-2-pyranone peaked at day 10 then vanished, indicating an early AA driven phase. 5-Hydroxymethylfurfural accumulated in all sugar-containing systems (16.16-98.73 μg/g at day 40) and increased continuously, marking late-stage browning. Redundancy analysis (96.75% variance) and structural equation modeling identified AA degradation (0.72) and MR (0.89) as dominant direct drivers. These results provide time-resolved compositional targets to mitigate discoloration in fermented vegetables for better quality preservation.