The emulsion stabilizing properties of a variety of food protein products in relation to their water (WAC) and oil (OAC) uptakes and the viscosity of the external phase were investigated. Protein products were treated as two entities for regression analysis. Emulsion instability of protein products with a lipophilic water-oil absorption index could be explained and accurately predicted on the basis of the WAC, OAC, and viscosity. Emulsion instability of protein products with a hydrophilic water-oil absorption index could be predicted using WAC and viscosity. High WAC, OAC, and viscosity of protein products were associated with optimum stabilizing properties.

An index for describing the relative hydrophilic-lipophilic character of proteins was proposed based on the measurement of the "spontanoeous water and oil uptake." The water-oil absorption index (WOAI) showed a defined correlation with emulsifying capacity (EC) for most proteins making it possible to predict EC in a simple way. Maximum emulsion capacity was achieved when the WOAI was nearly two, that is when the protein absorbed twofold more water than oil. Proteins with WA01 greater than two had increasingly hydrophilic characteristics and concomitantly increasingly low EC. Proteins with WOAI lower than two showed increasingly lipophilic characteristics and concomitantly increasing low emulsifying capacity. The finding of this study supports the concept that emulsifying capacity of proteins depends on the suitable balance between the hydrophilic and lipophilic characteristics, rather than merely high values for each one.

A simple method was developed for determining the spontaneous oil uptake and the kinetics of oil uptake by several food protein materials. The amount q of oil taken up by a protein powder during time t was described by the equation q = Qtf(B + t), where Q is the total oil uptake at equilibrium mad B is the time required to sorb QI2. The rate of oil uptake was proportional to the square of the amount of oil that must still be absorbed to reach equilibrium. A specific rate constant for the process was calculated as (BQ} -1 and an initial rate of oil uptake as Q/B.