Date of Award


Degree Type


Degree Name

Doctor of Philosophy


Food Science and Technology

Major Professor

Ada Marie Campbell

Committee Members

Roy Beauchene, Margaret N. Perry, Grayce E. Goertz


Two commercial soy protein products, Promine-D (a soy isolate) and Promosoy-100 (a soy concentrate), with protein contents on a moisture-free basis of approximately 97 and 72% respectively, were studied. Part A of the study was,an investigation of protein solubility, hydration capacity, emulsion properties, fat absorptivity, and thickening function of the soy products in simple systems at pH levels of 5.0, 6.0, and 7.0 and at temperatures of 4 °, ambient (22-25°), and 90°C. The soy products were compared on both equal sample weight and equal protein bases. Part B involved evaluation of the functional performance of the soy products, compared on an equal protein basis, in food system base products and dips formulated from the base products. Base products prepared at pH 5.0 and 6.0 and held at 4 and 90°C were evaluated for emulsion stability and apparent viscosity. Dips were held and evaluated at 4° by a consumer panel for viscosity, mouthfeel, oiliness, flavor, and general acceptability. The findings of Part A were related to those of B to evaluate the degree to which the simple system measurements could predict functional performance of the soy protein products in the food system selected.

The isolate (P-D) was more soluble than the concentrate (P-100) at all pH-temperature combinations. Solubility of both soys generally increased as the pH of the dispersion increased. Solubility of P-D increased as temperature increased from 4°C to ambient, whereas the response of P-100 depended on the basis of comparison, sample weight or protein. Solubility increased for both P-D and P-100 as the temperature was increased from ambient to 90°C. Hydration capacity, expressed as percent water absorption, generally paralleled solubility.

P-D, the isolate, was a more effective emulsifier than P-100. The soy products differed in their overall response to pH and temperature. Generalization is complicated further by a strong interdependence of pH and temperature effects and by the dependence of P-100's emulsifying performance on its use on the equal sample weight or equal protein basis relative to P-D.

Percent fat absorption of P-D was greater than that of P-100 at pH 7.0 at all temperatures studied. Maximum fat absorption of P-D occurred at ambient temperature, whereas that of P-100 occurred at 4°C. The fat absorption response of P-100 to temperature depended on its use on the equal sample weight or equal protein basis relative to P-D.

P-D and P-100 were compared as to dispersion viscosity only on the equal protein basis. P-D dispersions exhibited greater apparent viscosity than did P-100 dispersions at all pH-temperature combinations. P-D dispersions decreased and P-100 dispersions increased in apparent viscosity as the pH increased from 5.0 to 7.0. For both soys the apparent viscosity was minimal at ambient temperature and increased slightly at 4° and dramatically at 90°C.

Of the measurements made on simple systems, emulsion stability and viscosity were applicable to the base products used for dips. In addition, the consumer panel evaluated the dips from the standpoint of oiliness and viscosity, as well as smoothness, which is closely related to solubility.

All base product emulsions were stable when held at 4°C. P-D products were unstable at 90°C, particularly at pH 5.0, whereas P-100 products were stable. The consumer panel rated dips made with P-100 as more oily than those made with P-D, but the dips presented to the panel had been held only at 4°C.

Contrary to the results with simple systems, P-D base products were less viscous than corresponding P-100 products. Similarly to the results with simple systems, apparent viscosity of P-D base products decreased with increased pH; on the other hand, apparent viscosity of P-100 base products increased with increased pH. Apparent viscosity of base products made with both soys was higher at 90° than at 4°C; this response paralleled the temperature response of both soys in simple systems. The consumer panel rated both P-D and P-100 dips as more viscous at pH 5.0 than at 6.0.

Mouthfeel, representing smoothness of the dispersion, was rated higher at pH 6.0 than at 5.0. This response paralleled the solubility results for simple systems. The panel preferred the flavor of dips prepared at pH 5.0. They also gave these dips higher overall acceptability ratings than those prepared at pH 6.0.

Many interactions were observed throughout the study. In addition, simple and complex systems sometimes differed in their response to variations in pH and temperature. Therefore, extreme caution is needed in extrapolation of results from simple systems to food systems.

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