Unveiling the structural properties of three pectin fractions variation affecting pulp browning during peach processing.

Peach ripening accompanying by processing browning exacerbated has not been clarified in perspective of pectin fractions structural variation. This study investigated pectin fractions of water-soluble (WSP), trans-cyclohexane-1,2-diaminetetraacetic acid-soluble (CSP) and sodium carbonate-soluble (NSP) pectin in peach with different ripening times (24, 48, 72 h) and pretreatments (cold shock, CaCl2, the combination) effect on pulp browning in processing. Results showed that extended ripening time increases browning index and rate, along with increased reactive oxygen species levels, polyphenol oxidase and pectinase activities, and the structural of the pectin fractions. Thereinto, weight-average (Mw) and number-average (Mn) molecular weight of WSP increased, its linearity and branching degree decreased, while CSP and NSP showed decreases in Mw, Mn, and branching degree, but increases in linearity, rhamnogalacturonan structure proportion, and bending degree. Browning was correlated positively with Mn, Mw, rhamnogalacturonan proportion of WSP and CSP, linearity and bending degree of NSP, while negatively correlated with Mw of CSP and NSP and esterification degree and branching of all fractions. Thus, maintaining pectin polydispersity and rhamnogalacturonan branching helps protect the system from being quickly browning by compartmentalization effect of hindering the polyphenol substrates and enzymes possibly effective. This study offers insights into controlling browning through pectin fractions modulation.