Dairy Systems - Practical Food Rheology - page 166

of liquid foods. As previously stated, one major goal of instrumental
tests, including rheological measurements, is to relate the results with
sensory perception. It is challenging to find a good correlation between
instrumental test and oral perception because humans simultaneously
detect many aspects of material properties including flavor, aroma, tex-
ture, appearance, color, and sound (Nishinari, 2004). The processing
occurring in the mouth during eating can have a big impact on sensory
perception. Therefore, the effect of oral processing should be considered
in interpreting the rheological results.
Factors contributing to the final texture perception are initial product
characteristics, oral processing, the stimuli from the receptors and their
integration in the brain to a conscious perception (van Vliet et al ., 2009).
Recently, the role of oral processing in sensory perception has been
the subject of much interest. Important processes in the mouth during
chewing solid foods such as cheese include fracturing during biting
and chewing, water uptake, dissolving, lubrication, bolus formation,
swallowing and clearing (van Vliet et al ., 2009). Hutchings and Lillford
(1988) proposed that food will be swallowed only after its structure has
been broken down far enough to obtain particles below a certain size
and the food has been moistened sufficiently by saliva, allowing the
formation of the bolus. The size of the bolus that is swallowed depends
on foods and the ability of individuals to grind foods. The swallowing
threshold is affected by product characteristics and oral physiology
such as the saliva flow rate. Using computer simulations to study the
chewing of Brazil nuts and raw carrots, Prinz and Lucas (1997) found
that the masticatory system of humans is highly responsive to changes
in food texture. During mastication of solid foods, the particles mix
with saliva and form more or less a coherent bolus. Food particles could
also stick to the oral mucosa. Factors determining whether particles
aggregate or stick to the mucosa are the work of adhesion between
food-food and food-mucosal interfaces, the surface tension of fluid in
the mouth, its viscosity and the frictional resistance needed to displace
food particles from the mucosa by the tongue (Prinz and Lucas, 1997;
Lucas et al ., 2004). For semi-solid dairy products, sensory attributes
that are important to consumer perception are firmness, crumbliness,
creaminess, stickiness, spreadability, and consistency (van Vliet et al .,
2009). Oral processing between the tongue and palate becomes more
important with adhesion and creaminess. Important textural attributes
of liquid foods include thickness, sliminess, creaminess, roughness,
fattiness, and the after-feel texture of the coating formed on the mucosa
(van Vliet et al ., 2009). Oral processing mainly involves the tongue,
which pushes down the throat followed by swallowing.
In order to get a clear understanding of the texture perception of
solid foods, a thorough background in fracture mechanics and the