THE EFFECTS OF SOY PROTEIN ISOLATE ADDITION ON THE PHYSICO-CHEMICAL PROPERTIES OF GUMMI CONFECTIONS

The effects of soy protein isolate incorporation on the physico-chemical properties of starch-based gummi confections were investigated using thermal and rheological analyses, as well as supportive sensory and spectroscopy studies. The overall objectives of this study were to characterize the textural and rheological changes upon varying levels of soy addition to starch confections and consequent changes to quality parameters and second to assess the impact of incorporation of soy protein isolate on storage stability. Texture profile analysis was conducted to simulate mastication and to quantify, along with a hedonic sensory panel, the effects on gummi acceptability as a function of texture. Increasing levels of soy protein yielded samples that were progressively less firm and cohesive, caused either by starch network dilution and/or disruption. The softening effect of soy protein was observed throughout storage. Addition of soy protein improved the texture acceptability, presumably by decreasing perceived shortness, a texture defect associated with overly-firm gelled confections. Rheometric analyses were conducted to determine the relationship between gummi viscoelastic properties and the applied stress and rate thereof. Addition of soy protein was found to progressively decrease the yield stress to suppress yield stress increase at each storage interval. The viscoelastic crossover frequency, an indicator of stability, was also found to decrease as soy protein concentration increased and to have a lower rate of increase during storage.Water-dependent interactions were characterized as they relate to soy concentration and storage time. Thermogravimetric analysis results indicated that the primary water population was more easily removed in high-soy protein formulations. Additionally, as storage time increased, soy protein maintained relative homogeneity of the primary water population and removal of water required lower temperatures with the soy formulation, indicating less entrapment of water throughout the storage period studied.Results from differential scanning calorimetry did not indicate a significant shift in the glass transition temperature as soy concentration increased, likely due to the low concentration of plasticizing water. Neither gummi system exhibited distinct endotherms associated with starch melting regardless of treatment; soy protein inclusion did not prevent complete starch gelatinization during the confection process, as evidenced by the lack of the typical starch melting endotherm. However, the addition of soy protein was able to prevent an increase in the Tg of the gummi confections, perhaps by interfering with starch re-association.The changes in monomeric anthocyanin quantity, expressed as units of cyanidin 3-glucoside, which occurred as a result of confection processing were also analyzed using ultraviolet spectroscopy. The soy gummi confections yielded higher anthocyanin recovery, perhaps due to the greater heat dissipation caused by a lower cooking viscosity. Hedonic sensory analysis showed that addition of soy protein improved acceptance for texture and flavor. The mechanism of improvement is thought to be related to the decreased shortness of the product which augments mouth-feel and flavor release. All results indicate that soy protein has potential as a processing aide in gelled confections by modulating physical properties: decreasing gel rigidity, improving sensory characteristics, improving natural pigment recovery, and homogenizing water populations.