CHANGES TO PECTIC AND HEMICELLULOSIC POLYSACCHARIDES OF KIWIFRUIT DURING RIPENING

Cell walls of kiwifruit consisted of 40–50% pectic substances, 15–25% hemicellulose, 25–35% cellulose and 1–7% protein. Relative amounts of each type of cell wall polysaccharide varied among different tissue zones of the fruit, as did the onset of cell wall breakdown during ripening. Ethylene induced ripening in the outer pericarp was accompanied by solubilisation of pectic polymers and removal of galactose from the side chains of the pectic polysaccharides. Pectic polymers were initially solubilised without detectable change to either primary structure or molecular weight. Concurrent changes occurred in the inner pericarp but not in the core or locule walls, where cell wall breakdown was much less marked 7 days after an ethylene treatment. There was a decrease in the molecular weight of the hemicellulose xyloglucan fraction during ripening but no change in either the 4-O-methylglucuronoxylan or galactoglucomannan hemicellulose fractions. Results are discussed in relation to the possibility that initial cell wall dissolution during ripening occurred in the absence of pectin-degrading enzyme action.