Opposite shapes appearing on the PCA biplots are significantly
differentiated by the Duncan test. The Wing and the Sail were
significantly more intense in cocoa than the Trapezoid, Round and
Rectangle shapes (Fig. 5a). Despite caramel flavour being perceived
at very low intensities (mean scores < 1), results showed that the
Trapezoid shape was significantly more intense than the Rectangle,
Ellipsoid and Oval shapes (graph not shown). The Sail shape
aftertaste was significantly more intense than for Triangle, Oval and
Catstongue 1 shapes (Fig. 5b). As deformation, melting, and smooth
and powdery were strongly correlated, the focus from here on
would only be on melting and smooth attributes. The shape
perceived to melt the most was the Round. It was significantly more
melting than Ellipsoid, Sail, Wing, Trapezoid, Catstongue 2 and
triangle shapes. The shapes perceived to melt the least were
Ellipsoid, Sail and Wing (Fig. 5c). The Rectangle shape was
perceived significantly smoother than the Ellipsoid, the Sail, the
Catstongue 1 and the Wing shapes. The Sail and the Ellipsoid were
the least smooth samples (Fig. 5d).
From these results, the most promising shapes in terms of
flavour (high cocoa, high caramel notes and high aftertaste) were
the Wing and the Sail. However, both shapes did not gather the best
melting and smooth properties, while Round and Rectangle were
well delivering on texture (high melting, high smoothness).
To better understand the observed differences in texture and
especially on melting attribute, we went a step further by exploring
the physical mechanisms underlying the melting sensory attribute
in the specific conditions of the test. Differences in perceived
melting were expected as we know that modulating the shape
plays a role on the heat transfer occurring in the mouth. The
dominating heat transfer mechanism is heat conduction across the
parts of the chocolate surface being in direct contact with the oral
surface (Fig. 6). Thus, a shape with a small initial contact surface
area (ex. the Sail) is expected to melt slower than a shape with large
contact surface area (ex. Round).
In addition, a shape which is compact (e.g. a sphere), will melt
slower than a shape which is elongated (e.g. thin plate) since
internal heat propagation depends on the characteristic length of
the geometry. The compactness is therefore important to consider
for predicting the melting speed of shapes. It is quantified as surface
to volume ratio S/V. Keeping in mind that only a part of the total
surface of the shape is in contact with mouth elements during