This result indicated that part of the tiny bubbles seen in the
batters were lost later during heating or/and that not all of them
could expand appropriately during heating, resulting in a more
compact structure with a low number of air cells and with an
absence of interconnectivity for the 100% sucrose replacement level.
These circumstances could be related to two factors. The first is the
lower viscosity and limited structural complexity (lower viscoelasticity)
of the reduced-sucrose muffin batter, which may have favoured
bubble buoyancy: the batter should have the necessary
consistency to retain air during the baking stage. The second is the
excessively early thermosetting associated with the decreased
sucrose content and the lack of effect of the PD on the protein
denaturation temperature. As the premature thermosetting of the
protein matrix starts in the crust region, the heat transfer mechanism
is gradually converted from convection to conduction starting
from the surface. In turn, this lowers the heat transfer rate and
consequently the vapour pressure build-up, causing inadequate
expansion of individual air cells. As a result, the cell structure is
characterised by relatively small air cells with less interconnectivity.