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APPLICATION OF STRESS‐CONTROLLED ANALYSIS TO THE DEVELOPMENT OF LOW FAT SPREADS
Author(s) -
EVAGELIOU VASILIKI,
ALEVISOPOULOS STEFAN,
KASAPIS STEFAN
Publication year - 1997
Publication title -
journal of texture studies
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.593
H-Index - 54
eISSN - 1745-4603
pISSN - 0022-4901
DOI - 10.1111/j.1745-4603.1997.tb00120.x
Subject(s) - creep , viscoelasticity , rheometer , materials science , rheology , gelatin , shear stress , deformation (meteorology) , composite material , viscosity , shear (geology) , chemistry , biochemistry
ABSTRACT Creep testing was carried out on low fat commercial spreads at 3% (Promise) and 22.5% (Delight) fat content. A ‘full fat’ product (Flora margarine) and gelatin gels were also analysed to provide background understanding of the viscoelastic behaviour in the low fat samples. Increasing levels of applied stress deform both the Flora margarine and the gelatin gels which creep and eventually achieve steady flow. The linear creep compliance‐time dependency for a given stress/level of initial deformation was imitated by a mechanical model combining a Maxwell element in series with one or more Voigt elements, which exposed the elastic nature of gelatin associations as opposed to the ‘plasticity’ of a fat lattice. Deviations from linearity in gelatin gels and Flora margarine lead to a catastrophic disruption of networks and the termination of experiments due to excessively high angular velocities on the rheometer. The nonlinear regime in low fat spreads, however, produces a three part deformation‐time profile comprising creep with steady shear flow, accelerated rate of deformation, and a second level of flow (‘terminal'). The accelerated rate of deformation signifies the catastrophic disruption of the biopolymer matrix and results in a viscoelastic solution with suspended fat aggregates. The viscosity of this system (‘terminal') is much lower than the preceding steady shear viscosity before the yield point. Eventually, the fat aggregates break down leading to the sequence of viscosity collapse, excessive angular velocity, and experiment termination. The understanding achieved on phase behaviour and structural properties was used to develop economically water continuous spreads (5%–7.5% fat) without the undue gel‐like behaviour of Promise imparted by the gelatin component. The prototype spreads possess a stress‐strain profile under compression similar to that of Flora margarine at refrigerator temperature.