Postharvest quality losses of butter lettuce as affected by leaf age and temperature

Abstract

Whole lettuce plants were used to evaluate the effect of leaf age on ascorbic acid (AA), chlorophyll (C), microbial quality (M), colour and overall visual quality of fresh butter lettuce exposed at three isothermal environmental conditions: 0-2, 10-12 and 20-22°C during first 24 hours after harvest in order to describe quality changes in the product during transport from the field to the distribution center. Relative humidity was the optimal (97-99%). Temperature, leaf age and time significantly affected the quality parameters under study. Even though lettuces were stored under optimal temperature (0-2°C), significant C decreases were observed in outer leaves, increasing the loss at higher temperatures. The highest losses took place in the first 6 h, and then the rate of loss was significantly lower. Although the inner leaves presented changes in redness/greenness colour parameter, no significant changes in C were detected in these leaves. Increments in microbial counts occurred, and resulted higher in outer leaves respect to mid or inner ones. Increments were greater at higher temperature. Ascorbic acid significantly decreased at the three temperatures. After 6 h of storage, the AA losses were of 50% at 10-12 or 20-22°C, and of 30% at 0-2°C.