Influence of 1-methylcyclopropene (1-MCP) on ripening and cell-wall matrix polysaccharides of avocado (Persea americana) fruit

West Indian-type avocado (Persea americana Mill. cv. 'Simmonds') fruit were treated with two different concentrations (0.09 and 0.45 mul l(-1)) of 1-methylcyclopropene (1-MCP) for three exposure times (6, 12, and 24 h) at 20 C. The fruit were then stored at 20 C in ethylene-free air for ripening assessment. Firmness, weight loss, respiration and C2H4 production, peel color, cell-wall enzymes (polygalacturonase (PG), pectinmethylesterase, alpha-,beta-galactosidase, and C-x-cellulase) and cell-wall matrix polysaccharides (polyuronides and hemicellulose) were monitored during storage. 1-MCP treatment at 0.45 mul l(-1) for 24 h at 20 degreesC delayed the ripening of avocado fruit by 4 days at 20 C. This delay was characterized by a significant reduction in the rate of fruit softening and in the timing and intensity of the ethylene and respiratory climacterics. Avocado treated with 1-MCP (0.45 mul l(-1)) for 24 h at 20 C also showed significantly less weight loss and retained more green color than control fruit at the full-ripe stage (10-20 N). The delay in avocado ripening was influenced by 1-MCP concentration, exposure duration, and exposure temperature. 1-MCP treatment affected the activity trends of all cell-wall enzymes measured and completely suppressed increases in PG activity for up to 12 days. Consistent with the activity trends of PG, polyuronides from 1-MCP treated fruit when fully ripe exhibited less extensive molecular mass downshifts compared with the control fruit. The data indicate that the primary phase of avocado fruit softening occurs in the absence of appreciable PG activity. 1-MCP treatment also delayed and slightly reduced the depolymerization of 4 M alkali-soluble hemicelluloses, including xyloglucan. (C) 2002 Elsevier Science B.V. All rights reserved.