Impact of freezing storage on the structure integrity of pectin in Eureka lemons

This study systematically examined freezing-induced pectin modifications in whole Eureka lemons by analyzing water-soluble (WSP), trans-1,2-cyclohexane diamine tetraacetic acid-soluble pectin (CDTA)-soluble (CSP), and sodium carbonate-soluble (NSP) pectin fractions under different freezing conditions. Comprehensive analyses included content measurement, monosaccharide composition, and structural characterization using Fourier transform infrared spectroscopy (FTIR), molecular weight determination, nanoparticle size analysis and nuclear magnetic resonance bop (NMR). Results demonstrated significant pectin redistribution: long-chain WSP decreased substantially while long-chain CSP increased remarkably. Freezing triggered homogalacturonan depolymerization in CSP, whereas NSP maintained short-chain structures with minimal side-chain loss. Structural analyses revealed coexisting α- and β-configurations . Freezing storage notably reduced the degree of methyl esterification and molecular weight of WSP, while increasing its nanoparticle size. This study elucidated the distinct freezing damage mechanisms of the three pectin types. The composition and structure of citrus pectin were regulated by selecting appropriate freezing methods, thereby enhancing the structural stability of frozen lemon.