Comprehensive analysis of Maillard reaction products coupled with lipid and protein oxidation in walnuts subjected to different drying methods.

This study evaluated five drying methods [natural drying (ND), hot-air drying (HAD), far-infrared drying (FIRD), far-infrared combined hot-air drying (FIR-HAD), and vacuum drying (VD) on Maillard reaction products (MRPs) and lipid-protein oxidation in shelled walnuts. Advanced glycation end products (AGEs: carboxymethyllysine/CML, carboxyethyllysine/CEL, methylglyoxal-derived hydroimidazolone/MG-H1, argpyrimidine/Arg-p), α-dicarbonyls (3-deoxyglucosone/3-DG, glyoxal/GO, methylglyoxal/MGO), and oxidation markers were analyzed. Results showed that VD yielded the highest protein carbonyls, total AGEs, and CML. However, HAD produced the lowest total AGEs, CEL, MG-H1, and Arg-p, but the highest fructosamine and GO levels (1.2-1.5 and 1.3-2.7 times higher than those of other treatments, respectively). Relative to the other four drying methods, HAD reduced CEL, MG-H1, Arg-p and total AGEs by 8.4%-42.7%, 14.3%-34.5%, 34.6%-46.8% and 19.3%-34.1%, respectively. FIR-HAD was characterized by elevated MGO, Arg-p, peroxide value (POV), and CEL. ND showed the highest CEL content. Principal component analysis and heatmap visualization revealed distinct clustering patterns among the five treatments. Correlation analysis revealed complex links between lipid/protein oxidation markers and MRPs. These findings indicate that drying method strongly influences walnut quality, with HAD being preferable for minimizing total AGE accumulation despite elevated intermediate products.