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

Variable preheating conditions allowed the modification of the firmness of two green bean cultivars after processing. The aim of this study was to elucidate the biochemical basis of this phenomenon and to relate pectin differences to different inherent firmness of two cultivars. The preheating temperature, which resulted in the highest retention of firmness after sterilization, corresponded with the optimal temperature for pectin methylesterase activity. 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 molecular mass, were higher after sterilization. Firmness differences between the two cultivars seemed to be related to the degree of methylation, the degree of acetylation, and the total amount of pectins. Preheating of green beans affects texture after sterilization most likely by demethylation of pectin 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.