| Abstract
| - Variable preheating conditions allowed the modification of the firmness of two green bean cultivarsafter processing. The aim of this study was to elucidate the biochemical basis of this phenomenonand to relate pectin differences to different inherent firmness of two cultivars. The preheatingtemperature, which resulted in the highest retention of firmness after sterilization, correspondedwith 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, theyields of the buffer and chelator soluble fractions, as well as their average molecular mass, werehigher after sterilization. Firmness differences between the two cultivars seemed to be related tothe degree of methylation, the degree of acetylation, and the total amount of pectins. Preheating ofgreen beans affects texture after sterilization most likely by demethylation of pectin by pectinmethylesterase thereby (i) decreasing the β-eliminative degradation of pectin and (ii) increasingthe capacity of pectin to form Ca2+-mediated complexes. Keywords: Cell walls; pectin; food processing; preheating; Phaseolus vulgaris; pectin methylesterase;peroxidase; texture; firmness
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