CHANGES IN THE PECTIC SUBSTANCES OF APPLES DURING DEVELOPMENT AND POSTHARVEST RIPENING .1. ANALYSIS OF THE ALCOHOL INSOLUBLE RESIDUE

Cell wall material in the form of an alcohol-insoluble residue (AIR) was prepared from apples during growth and maturation on the tree and at different stages of ripening during postharvest storage. The galacturonic acid, neutral sugar, starch content as well as the degree of acetylation of the AIR were determined for each stage as was the degree of methyl esterification of the pectic substances. During the first weeks of development, the AIR content of the fruit decreased; it then stayed constant until the end of storage. The galactose and arabinose content of the AIR decreased with time while the galacturonic acid content stayed almost constant. Hardly any changes were observed in the degrees of methyl esterification and acetylation. The unripe fruit contained appreciable amounts of starch whereas none could be determined shortly after harvest. The significance of the losses of arabinose and galactose residues will be examined in a further paper.