English abstract
Date production in the world is only confined to a small number of countries, major
among which are the Arab countries. However, the date industry in the Arab world is not
yet fully developed and concerted efforts are still needed to fully utilize the tremendous
potential of date substances as ingredients in processed foods for export and the local
market. Date pectin is particularly promising since it should be possible to find
applications as a thickener or gelling agent in high solids foods (confectioneries, jams,
table jellies, processed cheeses, etc). Product development on a sound technological
basis requires adequate characterisation of the physicochemical properties of date
pectin in conjunction with those of citrus pectin, which the former is aimed to replace in
foodstuffs. In view of the above, the Thesis undertakes an overall characterisation of the
date ingredients from pollination to traditional launching of the fruit to the market. It was
found that astringency closely followed levels of the fresh weight tannin content. The
dates decreased in firmness as they matured through a process of de-esterification, not
through a decrease in the amount of pectin present. De esterification should allow
polygalacturonase to attack the polygalacturonic acid, decreasing the molecular weight
of pectin, thus contributing to softening. Changes in chemical characteristics can
significantly alter the functionality of the molecule thus allowing design of 'tailor-made'
food products. The chemical properties of citrus pectin are well known but there is a
lack of fundamental understanding of the structural behaviour in high solids systems.
This was achieved by employing sophisticated rheology and applying, for the first time,
the theoretical framework of Williams, Landel and Ferry, which demonstrated that high
sugar/pectin mixtures exhibit a classic glass transition. Future research should address
the effect of molecular weight and degree of esterification of the date pectin on
viscoelasticity in an effort to utilize the macromolecule in traditional foods and novel
appealing formulations.
