Defining the sorption isotherms of Deglet Nour dates stored in Tunisia.

摘要

Sorption isotherms determine the hygroscopicity in dates and anticipate the impact of any variations in the ambient relative humidity (RH) on the moisture content of the fruit during storage. Such isotherms help maintain a premium quality fruit. Dates were placed in storage rooms with increasing rates of relative humidity controlled with appropriate saline solutions. The moisture content of the dates was followed until the moisture exchanges between the fruit and its surroundings had reached an equilibrium. Dry and semidry Deglet Nour dates were used for the experiment. The analysis of the moisture content of both types of fruit, stored at 25deg C, was performed on two batches of dates: natural untreated dates and treated dates coated with a glucosemixture. With a RH inferior to 50%, both types of dates experienced dehydration which was all the more significant when the RH was low. With a RH exceeding 50%, hydration increased as the ambient RH rose. For the same RH, recorded gains and losses in water were lower in treated dates than in untreated dates. The glucose mixture therefore appeared to act as a physical barrier preventing the surrounding moisture from penetrating the fruit itself. The use of sorption isotherms and the coating of dates should help extend the longevity of the stored fruit as well as protect its quality.