New evidence on pectin

Evidence on mechanism of instantaneous pressure softening of asparagus lettuce under high pressure processing was explored with respect to pectin methylesterase activity, degree of methylation of pectin, degree of methylation patterns of pectin fractions, and pectin distribution in cell wall matrix. Instantaneous pressure softening was observed at 300？MPa, while texture recovery was obtained at 500？MPa. Pectin methylesterase activity was not significantly affected at 100 and 300？MPa, but dramatically activated at 500？MPa (p？<？0.05). Correspondingly, the degree of methylation of pectin decreased as pressure rose. Results of in situ immuno-dot blotting and immunolabeling based on specific bindings of antipectin antibodies showed a significant reduction of chelator-soluble pectin at 300？MPa, in contrast to a remarkable increase at 500？MPa. High pressure processing-induced demethoxylation was further verified by the enhanced fluorescence intensity of LM19 (an antihomogalacturonan antibody specifically binds to nonmethoxylated pectin) immunolabeled pectin, which was mainly located in tricellular junctions at 300？MPa, but covered the full cell surface at 500？MPa. In conclusion, instantaneous pressure softening of asparagus lettuce is strongly associated with loss of chelator-soluble pectin at 300？MPa