Proteomic and Amino Acid Dynamics During Jujube Blackening: Structural Transformations and Maillard Reaction Linkages

In this study, the structural characteristics of proteins and the amino acid composition during the jujube blackening process were investigated, with a particular focus on their relationship to the Maillard reaction. The reaction induced disruption of protein covalent bonds and altered protein aggregation states, with the most significant structural changes observed at 78 h. Blackened jujube exhibited elevated levels of pyruvate dehydrogenase and a higher content of hydrophobic amino acids compared to hydrophilic ones, both of which facilitated the progression of the Maillard reaction. The contents of total and free amino acids underwent marked changes throughout the blackening process, with substantial reductions in most amino acids, except for a few. After darkening, valine was identified as the most abundant essential amino acid, accounting for 68.69% of the total amino acid content, while cysteine was the most prevalent nonessential amino acid at 13.38%. The protein with the highest abundance had a molecular weight of approximately 60 kDa. Overall, this study elucidates the effects of the Maillard reaction on jujube proteins and amino acids and provides a theoretical foundation for understanding the formation mechanism of blackened jujube.