Insights into the structural alterations of different pectin fractions and their impact on enzymatic browning during apple pulp processing.

Apple pulp browning is closely related to polyphenol enzymatic oxidation and cell wall structural alterations during processing. This study investigates the structural characteristics of water-soluble pectin (WSP), chelate-soluble pectin (CSP), and sodium carbonate-soluble pectin (NSP), and their variations' impact on enzymatic browning in browning pulp (BR), CaCl pretreated pulp (CA), and fresh control (FC) apple groups. In BR, pectin degradation involved altered chain conformations, reduced RG-I branching in CSP and increased RG-I linearity in NSP, leading to compromised cell wall integrity. Conversely, CaCl pretreatment enhanced esterification and promoted formation of characteristic linkages (1,3-α-Galp, 1,4-β-Galp, and T-β-Galp) in WSP, contributing to reduced browning. Additionally, CaCl stabilized cell wall by reinforcing cross-linking in CSP and NSP, particularly within RG regions, thereby limiting their conversion to WSP, and maintained high molecular weight in NSP due to a high HG content. These findings highlight the crucial role of pectin structure in enzymatic browning.