The focus of this thesis is the area of staling of Arabic flat bread (or pita bread). The
reductions in shelf life due to bread staling cause significant economic losses in the
Middle East where preservatives are not permitted. The aim was to investigate whether
processing solutions could solve this problem.
A commercial bread produced in Kuwait was initially studied. The industrial baking
process was monitored closely, and the products analyzed for moisture content in
Kuwait after storage at 4 and 20 °C. Representative samples were ground and freezedried
in Kuwait, and transported to the UK for analysis by Differential Scanning
Calorimetry (DSC). The findings from this study showed moisture content variations
between different bread formulations after baking, however the DSC analysis was
inconclusive due to possible changes in the freeze dried bread.
The industrial process was thus replicated as closely as possible at Loughborough
University so that the bread could be analysed immediately after baking and after up to
3 days storage. It was also found that high pressure stainless steel pans produced
better DSC baseline stability compared to aluminium pans due to suspected leakage of
the latter (used in literature studies), and were thus used for the rest of the study.
Attention was also paid to the possibility that different parts of the bread receive
different radiant heating intensities during baking as evidenced by the different degrees
of brown coloration. This showed that whilst almost complete gelatinisation initially
occurs, the highest levels of subsequent retrogradation occurred in an area
intermediate between the centre and outside of the pita bread. This coincided with the
region with the highest moisture content immediately after processing (and likely to
receive the least amount of heat). A parallel study using DSC which subjected dough
samples to a temperature profile similar to that found in baking also found that lower
heating rates (with albeit higher heat exposure) produced greater amounts of
retrogradation. In each case moisture contents during storage were comparable
between samples, thus indicating that heating rates during processing is a key
parameter governing subsequent retrogradation, and also that future studies should
identify the sampling position within the bread when performing analyses.
Thermocouple studies showed that the temperatures in the steam pocket that develops
during puffing were close to that of the boiling point of water. Consequently, a further
study was also performed in which Arabic flat bread samples were baked at different
pressures (up to 2 bar) in a novel high pressure oven. The motivation was that
changing pressure to increase baking temperatures could be a way of using processing
rather than formulation methods to extend shelf life. Whilst applying pressure was
found to retard subsequent retrogradation, it did result in breads becoming firmer
during storage which was not the desired effect. However, this may be a consequence
of the slightly lower moisture contents found in the bread baked at higher pressure.
A Doctoral Thesis. Submitted in partial fulfillment of the requirements for the award of Doctor of Philosophy of Loughborough University.