CHANGES IN PECTIC AND HEMICELLULOSIC POLYMERS OF GREEN BEANS (PHASEOLUS-VULGARIS L.) DURING INDUSTRIAL PROCESSING

Pectic and hemicellulosic material was extracted from the alcohol-inso luble residues of two fresh and industrially processed green bean vari eties. The carbohydrate compositions and relative molecular masses of these fractions were determined. Fresh beans of cv. Odessa contained m ore pectin and hemicellulose but less cellulose than cv. Masai. The ma jor changes occurred during sterilization and concerned the pectic pol ymers. In fresh beans the major part of the pectins was most likely co valently linked to other cell wall polymers since they were extractabl e only after mild saponification of the cell wall. Sterilization resul ted in degradation and solubilization of pectic polymers from the cell wall and middle lamella. The galacturonic acid backbone was partially degraded. Side chains, however, were not removed from the pectic poly mers, resulting in an accumulation of branched pectins of low molecula r mass in the buffer-soluble fraction. The amount of cyclohexane-trans -12,-diaminetetraacetate-soluble material showed a small increase afte r blanching, but the amount after sterilization was the same as compar ed with the fresh material. These results confirm the hypothesis that pectins are solubilized by degradation of the galacturonic acid backbo ne during industrial processing. The changes in pectic polymers during processing are summarized in a scheme. No significant changes were ob served in the hemicellulose and cellulose fractions.