Changes in firmness, pectin content and nanostructure of two crisp peach cultivars after storage

To investigate the fundamental of firmness changes of crisp peaches, firmness and pectin contents of two peach (Prunus persica L. Batsch) cultivars (‘Cangfangzaosheng’ and ‘Songsenzaosheng’) stored at 2 °C, 8 °C and 15 °C were investigated. Sodium carbonate-soluble pectin (SSP) extracted showed the highest correlation (positive) with firmness among the three kinds of pectins (water-soluble pectin, chelate-soluble pectin and SSP). The qualitative and quantitative information about SSP nanostructures were determined by atomic force microscopy (AFM). The widths of the peach SSPs were very consistent. The SSP chain widths of both peach cultivars were similar and were composed of several basic units. Schematic models of the changes of the chain widths were proposed. The results indicate that the firmness of peach was closely related with the contents and nanostructural characteristics of SSP, which might be hydrolyzed by enzymes in fruit flesh.