Changes in sugars, total protein, and oil in 'Hass' avocado (Persea americana Mill.) fruit during ripening

A better understanding of the post-harvest physiology of avocado (Persea americana Mill.) fruit is required to improve the post-harvest management of the crop. Two heptoses, D-mannoheptulose and perseitol, occur in unusually high concentrations in avocado tissues and are thought to be important in fruit ripening. We determined changes in the concentrations and relationships between individual sugars, total soluble proteins, and oil during fruit ripening. 'Hass' fruit were harvested from cool and warm sub-tropical areas in South Africa three-times during a single season. Dry matter increased during the season at both locations. For fruit from the cool sub-tropical climate, D-mannoheptulose and perseitol concentrations declined rapidly from 15.9 mg g(-1) dry weight (DW) and 7.9 mg g(-1) DW to 2.1 mg g(-1) DW and 0.6 mg g(-1) DW, respectively, 13 d after harvest. Overall concentrations of glucose and fructose were negligible at harvest and increased to 1.4 mg g(-1) DW and 0.8 mg g(-1) DW, respectively, during ripening. The concentration of glucose in fast-ripening fruit increased 3 d prior to increasing in slow-ripening fruit. The concentration of sucrose was intermediate (2.8 - 4.5 mg g(-1) DW) and was variable during ripening. The concentration of total soluble proteins increased during ripening from 17.8 mg g(-1) DW to 34.8 mg g(-1) DW, whereas the concentration of oil was fairly stable during ripening, and varied from 24.8 - 36.7% DW, depending on fruit maturity. It is suggested that the heptose pool is an important source of carbon and/or energy in avocado fruit. The low concentrations of these sugars and the rapid decline in their levels, post-harvest, indicate that optimal post-harvest management, especially cold storage and ripening temperature regimes, is necessary to reduce the risk of post-harvest disorders and to ensure a consistent supply of high-quality avocado fruit.