Contribution of various pectin fractions and internal condition to gel formation in wooly peach fruit during cold...

Peach fruits stored at 5 °C are prone to woolliness, mainly due to pectin gel. The gel capacity of different pectin fractions in vitro and the contribution of internal conditions were analyzed. Results indicated that compared with fruits stored at 10 °C, those at 5 °C had lower sucrose and higher glucose and fructose. Metal ion content, especially Ca²⁺, initially increased then decreased. Decline in pectin methylesterase activity was less than that in polygalacturonase activity. Water-soluble and chelator-soluble pectin (WSP and CSP) stored at 3 and 4 weeks formed gel with tissue fluid, whereas alkali-soluble pectin remained fluid. Low-field NMR and rheology confirmed these findings, which resulted from the relatively high molecular weight, low degree of esterification, and elevated homogalacturonan ratio. Sucrose and acidic conditions provided an environment conducive to gel and the elevated Ca²⁺ benefited for gel formation, providing direction for elucidating gel mechanism in peach fruit.