Preheating effects on the textural strength of canned green beans. 1. Cellwall chemistry

Variable preheating conditions allowed the modification of the firmness of two green bean cultivars after processing. The aim of this study was to elu cidate the biochemical basis of this phenomenon and to relate pectin differ ences to different inherent firmness of two cultivars. The preheating tempe rature, which resulted in the highest retention of firmness after steriliza tion, corresponded with the optimal temperature for pectin methylesterase a ctivity. After this preheating treatment, there was an overall reduction of the degree of methylation of the cell wall pectin. In addition, the yields of the buffer and chelator soluble fractions, as well as their average mol ecular mass, were higher after sterilization. Firmness differences between the two cultivars seemed to be related to the degree of methylation, the de gree of acetylation, and the total amount of pectins. Preheating of green b eans affects texture after sterilization most likely by demethylation of pe ctin by pectin methylesterase thereby (i) decreasing the beta -eliminative degradation of pectin and (ii) increasing the capacity of pectin to form Ca 2+-mediated complexes.