Biomedical Engineering Reference
In-Depth Information
In the oscillatory tests, samples are subjected to deformation or stress which varies
harmonically with time. Sinuosoidal and simple shear is typical [
62
] . This testing
procedure is the most common dynamic method for studying the viscoelastic
behaviour of food. Results are very sensitive to the chemical composition and phys-
ical structure [
62
]. Using a sinusoidally oscillating deformation of known magni-
tude and frequency, the phase lag angle between stress and strain is measured and
used to calculate the elastic (storage modulus or G¢) and viscous (loss modulus or
G″) components of a complex viscosity h *.
The rheological behaviour of the dough is determined by protein-protein inter-
actions at large deformations, while starch-starch interactions dominate at small
deformations. Therefore, empirical tests correlate well with the results of the baking
test [
64
], as the deformation that occurs is reasonably large compared with the
deformation applied during the creep and dynamic rheological tests. In contrast,
fundamental tests provide well-defined basic rheological information (viscosity and
elasticity) and provide better defined experimental conditions of stress and strain,
which allow results to be interpreted in fundamental units. Although various types
of tests and instruments have been developed to describe dough performance during
processing, it is fair to say that no single technique could completely describe its
rheological behaviour.
3.5.2
Innovative Approaches
3.5.2.1
Image Analysis
Recently, image analysis has been introduced to evaluate the quality of foods,
including baked goods. This technique uses protocols based on image digitalization
at the macro- and micro-structural level through different systems (e.g. scanners,
video cameras and microscopes). Image analysis provides a rapid and objective
definition of the morphological and densitometrical characteristics of single objects
or complex structures (Fig.
3.10
). It makes it possible to study and model the phe-
nomena that occur during processing continuously or even on-line [
65,
66
] .
The analysis of an image requires a number of passages: (1) image acquisition in
a digital format (a pixel image); (2) image pre-processing, to improve the image
while maintaining its original dimensions; (3) image segmentation, to divide the digi-
tal image into separate, non-overlapping areas (e.g. to better distinguish the objects
from the rest of the image, such as the alveoli in a slice of bread); (4) measurement of
objects, to determine their different characteristics (size, shape, colour, texture); and
(5) classification, to identify the objects by classifying them into different classes [
67
] .
When used for baked good processing, image analysis allows the determination of
several parameters such as the increase of volume, changes of shape, time needed to
complete the dough development, extent and distribution of the alveolar structure
during leavening, initial increase and successive contraction of volume, and gelatini-
zation of the starch and surface browning during baking [
68
] .
