Functionality of plant proteins for comminuted meat systems
Creators: name: Paulson, Allan Thomas
Publisher: name: University of British Columbia
Year: 2010

description: A three part study is presented which examines the functional properties of plant proteins as they relate to textural and stability characteristics of protein-replaced meat emulsions. In the first chapter, the effects of cooking time (25 or 50 min) and temperature (70 or 95°C) on texture, microstructure and cook stability of a model meat emulsion system containing soy or canola protein isolate were investigated. The plant proteins were added either dry or rehydrated at replacement levels of 33.3% and 66.7% of the meat protein. Instrumental texture profile analysis and stability data revealed several complex interactions between experimental variables; however, level of protein replacement was predominant, with decreased firmness and increased yield resulting from increased replacement of meat protein. Thermorheological profiles of emulsions and protein dispersions demonstrated that the development of elasticity of all-meat emulsions during heating was essentially complete at 75-80°C, while the elasticity of canola or soy protein dispersions continued to rise with heating to 95°C. A meat emulsion containing canola protein displayed characteristics of the all-meat emulsion and canola protein dispersion thermoprofiles, but the increased structure formation from the canola protein at higher heating temperatures did not fully compensate for an initial decrease in elasticity that resulted from the loss of meat protein. Although there were slight differences in the fat particle distributions of the emulsions containing plant protein, the distributions had similar shapes, where particles larger than 50 micrometers approximated a normal distribution, and were thought to be relatively intact fat cells while the number of particles with diameters of 10-50 micrometers increased in an essentially logarithmic manner as size decreased. The microstructure of the proteinaceous matrix was affected primarily by protein source, replacement level and cooking conditions. In chapter 2, thermally induced gelation (72°C, 30 min heating) and emulsification properties of unmodified and succinylated canola protein isolate (54% and 84% modification of free amino groups) were examined over a wide range of pH values (pH 3.5-11.0) and sodium chloride concentrations (0.0-0.7M). Succinylation improved the gelation ability of canola isolate. For the unmodified isolate, gels formed at only 4 of 18 combinations of pH and NaCl concentration, while 12 gels formed from each level of succinylation under the same conditions. Above pH 6.5, succinylated protein formed gels only in the presence of NaCl. In general, the firmest gels were obtained with the moderate level of succinylation. Translucent and opaque gels responded differently to Theological tests and were related in different ways to the physicochemical and Theological properties of protein dispersions. The viscoelastic properties of the translucent gels were affected mainly by protein solubility and hydrophobicity, while those of the opaque gels were related to solubility, hydrophobicity, zeta potential and apparent viscosity of protein dispersions. The types of bonds involved in gel formation and stability were tentatively identified as hydrophobic interactions and hydrogen bonds. With the succinylated isolates, gels were formed in the presence of calcium ions at a concentration an order of magnitude less than was required for similar gel strengths with NaCl, which has implications for exploiting the gelation ability of succinylated proteins in products where high concentrations of NaCl are undesirable. Both emulsification activity and emulsion stability were increased by succinylation, but exhaustive succinylation was not required to produce a significant improvement in these properties. Emulsification activity was related to protein solubility, hydrophobicity, zeta potential and flow behavior of protein dispersions, while emulsion stability appeared to be mainly a measure of resistance to creaming and was related to protein solubility, zeta potential, apparent viscosity of protein dispersions, and the difference in density between the aqueous and oil phases. The third chapter examined the relationship between textural measurements of canola isolate gels obtained by means of a puncture test with an Instron tester, and fundamental rheological parameters obtained from nondestructive dynamic shear measurements with a Weissenberg Rheogoniometer. Although the force required to rupture the gels, as measured by the puncture test, was poorly correlated with the viscoelastic parameters, the slope of the force-deformation curves to the point of rupture was well correlated with the storage and loss moduli of the gels. In addition, the area under the force-deformation curves to rupture followed a curvilinear relationship with the loss tangent of the gels. The response of translucent and opaque gels to the two types of rheological tests was not identical, which indicated that gel microstructure is an influential factor when evaluating gel rheological properties by destructive or nondestructive methods.