Liquid Foodstuffs Exhibiting Yield Stress and Shear‐degradability

Abstract

Two rheological properties of liquid foodstuffs often encountered in practice are the yield stress and the shear-degradabils'ty (irreversible time-dependence). Both these properties were determined for meat and yeast extracts using two rotational viscometers. The material constants were obtained and fitted with Bingham Plastic and Herschel-Bulkley models for the meat extracts. The shear-degradability exhibited by the yeast extract was quantified in terms of the energy required to destroy the material structure. Texture Studies 12 (1981) 39--46. All Rights Reserved. @Copyright 1981 by Food Journal of

Flow behaviour of semi-solid dairy desserts. Effect of temperature

“…According to Halmos and Tiu (1981), the area encircled between the ascending and the descending curves is an index of the energy per unit time and unit volume needed to eliminate the influence of time in flow behaviour.…”

“…Flow behaviour. Before analysing flow behaviour, the structure responsible for thixotropy was previously destroyed by shearing (Halmos & Tiu, 1981;Carbonell et al, 1991a;Nguyen et al, 1998;Abu-Jdayil, 2002). After testing several shearing conditions, for 5 min at 100, 200, and 300 s À1 shear rates, and analysing the hysteresis cycles, a previous shearing of 5 min at 300 s À1 was selected as the appropriate treatment to get a nule hysteresis area.…”

Olestra formulation and the gastrointestinal tract

“…This interpretation is valid as long as the flow curve is generated under a standardized testing protocol (e.g., sample handling, temperature, shear rate ramp, etc.) (26). A comparison of thixotropic areas measured for semisolid olestra and liquid sucrose polyester is shown in Figure 3.…”

“…3). The magnitude of thixotropic area enclosed by the ascending and descending portions of the flow curve can be expressed in terms of the energy per unit volume of sample being sheared, which indicates that thixotropic area is related to the energy required to break down the particulate network structure of the material being sheared (25,26). Therefore, thixotropic area may be interpreted as a relative measure of the solid-like structural strength or stiffness of a material that exists prior to shearing.…”

Dairy Systems

“…A hysteresis in the flow curve (shear stress vs. shear rate) suggests that shearing at high-shear rate modifies the material structure (Doublier and Durand, 2008). The area of the hysteresis loop corresponds to the extent of structural breakdown during the shearing cycle (Halmos and Tiu, 1981). Ramaswamy and Basak (1991) measured the flow behaviour of stirred yoghurts under three consecutive shear rate cycles (Fig.…”