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This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License
Article
Shear Rate Effect on the Viscosity of Homemade and Commercial Tomato Sauce
Author(s)
Virues-Delgadillo Jorge-Octavio, Lozada-Santillan Claudia-Karina, Bulbarela-Sampieri Carmen, Galán-Méndez Frixia and López-del-Castillo-Lozano Micloth
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DOI:10.17265/2159-5828/2017.10.003
Affiliation(s)
Facultad de Ciencias Químicas, Universidad Veracruzana, Lomas del Estadio S/N, Xalapa, Veracruz 91000, México
ABSTRACT
Rheological
characterization of tomato products is important not only for design of unit
operations, but also to optimize processes and guarantee high quality of food
products. Time dependence is related with structural changes due to shear rate.
Thus, rheological characterization as a function of time is extremely important
to understand the changes that occurred in food products during commercial
processes. However, these characterizations are rare in the literature for
tomato products. Those rheological properties depend of several parameters,
such as agronomic, structural and process parameters. In this study, the effect
of shear rate on the viscosity at room temperature (22 °C) of two kinds of
tomato sauce (homemade and commercial) is analyzed; using a Brookfield
viscometer model 4535, Lab-Line Instruments. Homemade sauce was prepared with
fresh saladette tomatoes from a local market. Rheological analysis was performed
at shear rates from 0.05 to 10.47 s-1; using all the spindles
available. Statistical analysis was made using LSD and Duncan tests with a
confidence interval of 95% (p-value of 0.05). It
was demonstrated that homemade and commercial tomato sauce behaved as a
thixotropic fluid, due to the typical decrease on viscosity samples observed
when testing time was increased. When tomato sauce is at rest, it has a gelled
tridimensional structure; and, as soon as a shear stress is applied, the
movement generates an alignment of tomato constituent chains in flow direction,
breaking physic entanglements and thus causing a decrease in viscosity as a
function of time. Furthermore, it was discovered that the viscosity of homemade
sauce was higher than the viscosity of commercial sauce. The latter may be due
to the pre-thermal treatment. During this unit operation, polymeric chains of
lycopene most likely break into smaller chains of isoprene, causing the
observed decrease in viscosity. Besides, commercial sauce contains additives,
seasonings, preservatives and thickeners that are not in a homemade sauce.
KEYWORDS
Food rheology, viscosity, shear rate, tomato sauce.
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