Post-harvest Processing of Dates: Drying, Disinfestation and Storage

Abstract

Progressive demand for better date quality led to the development of solar drying technology. Equilibrium relative humidity (ERH) and water activity (aw) are the most reliable criteria indicating the ability to safely store dates. ERH <65 % at 26 °C serves as a critical limit for date storage at the commercial level and ensures resistance to deterioration by microflora. The relationship between MC and ERH for Medjool, Khadrawy, Zahidi and Deglet Noor is established based on different studies. A solar dryer employing mechanical distribution fans was successfully implemented to integrate thermal disinfestation technology. It is based on the principle of transfer of hot air through a tunnel containing 3 tonnes of dates exposed for 3 h at 50 °C. By employing thermal disinfestation technology to replace methyl bromide (MeBr) fumigation, no effect on the organoleptic properties of dates was observed, while complete mortality of insects and high disinfestation levels for all dry date cultivars were achieved. The technology is currently implemented in all Israeli date packing houses to replace the MeBr fumigation. Vapormate™ is a fumigant that contains 16.7 wt.% ethyl formate in liquid CO2. It is registered in Israel to control date pests, such as Nitidulid beetles, at dosage of 420 g/m3 for 12 h at temperatures above 24 °C, as an alternative to MeBr for dates stored in bulk. The storage atmosphere containing a concentration of 60–80 % CO2 in a gas tight chamber was found to be effective in controlling pests and preserving the quality of dates and moisture content (MC) for 4.5 months storage period.