Modification of matrix polysaccharides during avocado (Persea americana) fruit ripening: an assessment of the role of Cx‐cellulase

The role of C x ‐cellulase (EC 3.2.1.4) in fruit ripening and softening is unknown. In the present study, avocado ( Persea americana ) fruit, a rich source of C x ‐cellulase, were examined to determine if the enzyme plays a role in ripening‐related hemicellulose metabolism. Hemicelluloses (4 M alkali‐soluble) from avocado fruit exhibited a very broad distribution of polymer sizes and an overall decrease in M r during ripening. Polymers affected were primarily those of large M r (relative molecular mass). The characteristic total hemicellulose M r distribution and changes with ripening were also evident for xyloglucan (XG), a putative substrate for avocado C x ‐cellulase. Hydrolytic activity toward hemicelluloses from preripe fruit was detected in crude buffer‐soluble protein extracts derived from ripe avocado mesocarp tissue. XG was also degraded, and in a pattern similar to that observed during ripening. Purified C x ‐cellulase also exhibited activity against specific components of isolated hemicelluloses; however, in contrast to the crude protein. C x ‐cellulase alone was without influence on the M r distribution of avocado XG. Protein depleted of C x ‐cellulase was capable of moderate XG depolymerization. We conclude from the present studies that the enzyme C x ‐cellulase is not involved in the ripening‐related depolymerization of XG in avocado fruit.