Morphological, structural and membrane changes in frozen tissues of Madjhoul date (Phoenix dactylifera L.) fruits

Abstract

Tissues of Madjhoul date fruits (Phoenix dactylifera L.) deteriorated during 10 months of preservation at temperatures between 0 and −18°C. The most obvious progressive damage was the appearance of bright yellow-brown spots of crystallized solutes. Injury was not detected in fruit tissues subjected to freezing and storage at lower temperatures (between −35 and −50°C). Ultrastructural observations indicated that freezing at the higher temperature range resulted in the rupture of various cellular compartments, whereas in fruits frozen at the lower temperature range both intracellular membranes and cell walls were intact even after 10 months. Microsomal membranes isolated from the latter fruits contained higher levels of proteins, phospholipids and vanadate-sensitive ATP-ase activity than membranes isolated from fruits frozen under higher temperatures. The results suggest that possible reasons for the faster deterioration of dates frozen at higher temperatures lie in damage to cell membranes and cell walls.