Fractionation and characterization of sodium carbonate-soluble fractions of cell wall pectic polysaccharides involved in the rapid mealiness of 'Hongjiangjun' apple fruit.

Apple flesh tends to turn mealy and textural deterioration commonly occurs during storage. The comparative investigation of three sub-fractions separated from sodium carbonate-soluble pectin (SSP) of 'Hongjiangjun' apples between crisp and mealy stages was performed to unveil the textural alterations related to mealiness. In situ immunofluorescence labelling showed that galactans declined in parenchyma cell walls during the fruit mealiness. FTIR analysis, monosaccharide compositions and structural polymers configurated that loss of rhammogalacturonan-I (RG-I) from SSP sub-fragments (S C0.0-P and S-M0.0-P) might be closely involved in the mealiness. The NMR spectroscopy revealed that loss of the substituted galactans from α -Rha p residues repeat unit in S C0.0-P constituting RG-I in crisp stage that subsequently converted to S-M0.0-P in mealy stage might be closely associated with the modifications of pectin in cell walls during mealiness. These findings provided novel evidence for understanding the underlying modifications of SSP polymers during the mealiness of 'Hongjiangjun' apples. [Display omitted] • The immunofluorescent signal of galactan in mealy apple cells was sharply weakened. • Apple mealiness altered the sub-fragments of sodium carbonate-soluble pectin (SSP). • The mealiness of apple involved the loss of galactan on the RG-I chain in SSP. • The fine structure of product of RG-I degradation were putatively established. [ABSTRACT FROM AUTHOR]