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THE EFFECT OF TEMPERATURE, GEOMETRY, GAP AND SURFACE FRICTION ON OSCILLATORY RHEOLOGICAL PROPERTIES OF MASHED POTATOES
Author(s) -
ALVAREZ MARÍA DOLORES,
CANET WENCESLAO,
FERNÁNDEZ CRISTINA
Publication year - 2007
Publication title -
journal of food process engineering
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.507
H-Index - 45
eISSN - 1745-4530
pISSN - 0145-8876
DOI - 10.1111/j.1745-4530.2007.00120.x
Subject(s) - rheometer , rheology , composite material , viscoelasticity , materials science , homogeneity (statistics) , potato starch , shearing (physics) , starch , chemistry , mathematics , biochemistry , statistics
Oscillatory data obtained for mashed potatoes made from fresh tubers from measuring geometries of different designs and sizes were analyzed and compared at the sample temperatures of 25 and 55C. The measuring geometries used were smooth parallel plates (PP40 and PP20, 40‐ and 20‐mm‐diameter plates, respectively); truncated cone and plate (CP 4/40, 40‐mm‐diameter cone having an angle of 4°); FL25 four‐bladed vane tool (diameter: 25 mm, height: 55 mm); and serrated parallel plate (SPP40, 40‐mm‐diameter plate). Three different gaps between plates were used (2, 1.5 and 1 mm) to simulate the range of aggregate spacing in fresh mashed potatoes. The measured oscillatory rheological properties were significantly affected not only by the sample temperature but also by the test geometry used and the friction of and gap between its shearing surfaces. Dynamic parameter values were higher at 55 than at 25C, possibly indicating the onset and propagation of gelatinization of the potato starch grains. Unexpectedly, test geometries with higher friction capabilities, such as the serrated plate and vane tool, presented lower viscoelastic properties compared with results of other test geometries with lower friction capabilities. This result provides evidence of the influence of other factors on the measured oscillatory rheological properties of the mashed potato, such as measurement accuracy of the rheometer at different very small strains, homogeneity of the temperature for the different samples, existence of a complex dependency on the possibly complex stress condition that is imposed on the material upon loading, or even samples being prone to drying. The effect of the variation of the gap between parallel plates on oscillatory parameters depended on the shearing wall friction. The study highlights the difficulty in reconciling rheological results from different sources and the need for standardized rheological test methods so that rheological interlaboratory results can be critically analyzed and compared.