Relationships between textural changes and the changes in linkages of pectic substances of sweet pepper during cooking processes, and the applicability of the models of interactions between pectin molecules

Pectins in the alcohol-insoluble solids of sweet pepper (Capsicum annuum L.) were fractionated by sequential extraction with various solvents, and the changes in molecular size of the pectins in each fraction before and after further treatment with either heat or chelating agents were also investigated. Gel permeation chromatography was used to elucidate the changes in linkages of pectins and the textural change of sweet pepper tissue during cooking processes, and to search for the real existence of some sub-types in an elaborate model proposed for the interactions between A-, B-, and C-types of pectins. Based on the observed correlations between the contents of pectin fractions and the firmness of sweet pepper tissue, it can be deduced that the major forces for maintaining the texture of sweet pepper during cooking processes come from the pectin molecules linked by heat-labile bonds and covalent bonds. Moreover, from the molecular-size distribution of each pectin fraction before and after further treatment with heat or chelating agents, it can be concluded that the models proposed for the interactions between pectin molecules and other cell-wall constituents in vegetable tissues are reasonable and applicable.