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A whipping method for the measurement of overrun and foam stability was developed. Using this method the characteristic foams formed by the following proteins were studied: sodium caseinate, milk protein isolate and whey protein. The method was able to detect differences between foams produced by different proteins. The effects of copper sulfate and proteose-peptone on egg white foams were studied to show the reliability of the method. It was demonstrated that the addition of I mM copper sulfate stabilized (p < 0.05) foams made from both fresh and powdered egg white. Addition of proteose-peptone (0.05% and 0.1%) reduced the overrun and destabilized egg white foams.

A collaborative study involving nine laboratories was conducted over four years to evaluate a rapid, simple and reliable whipping method for measuring overrun and foam stability. Effectiveness of the method was assessed by measuring the characteristics of foams formed by three protein solutions (5%): sodium cascinate, milk protein isolate, and egg white protein; identifying and systematically eliminating sources of variability. Major sources of variability were protein dispersing technique, the mixer, and the cart exercised by the operator during sampling and weighing. The method detected differences in foam stability between egg white, casein and milk protein isolate (pooled SD = 4.5) using different mixers.

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TurbidityThe overrun obtained by whipping whey protein isolate (WPI) was significantly (~~0.05) affected by changing pH. Heating WPI at pH 4.0 reduced rate and amount of overrun. The highest overrun values for unheated WPI were observed at pH 5.0 and 7.0 after heating at 55°C for 10 min. The maximum foam stability for unheated WPI was obtained at pH 5.0. Heat treatment had little effect on stability at pH 4.0 or 7.0 but at pH 5.0, 80°C for 10 min improved stability by 65%. Based on surface pressure data, the rate of adsorption of P-lactoglobulin interfacial films and the work of compression correlated with overrun, maximum overrun, overrun development and foam stability.Before whipping, the aggregation of whey protein isolate after pH adjustment was determined by transmittance at 500 nm using a Spectronic 700 spectrometer (Bausch and Lomb, Rochester, NY). The values were expressed as Tb = (l-T500) x 100. A value of 100 corresponded to a completely turbid solution (0 transmittance). Foaming propertiesThe effects of pH and heat treatment on the foaming properties of WPI were assessed using the method of Phillips et al. (l-987): Overrun was measured (3 replicates) using 75 mL whey protein isolate (5.0% w/w) solubilized for 30 min with adjustment to the appropriate pH (4.0; 5.0 or 7.0) using either O.lN HeI or O.lN NaOH.'Th&soluti&s were held for 10 min at 25, 55 or 80°C: cooled to 25°C in a water bath (10 min) then whipped-for 5-min iniervals for a total of 20 min using a Sunbeam Mixmaster mixer (Sunbeam Corporation, Oak Brook, IL.). The amount of air incorporated was measured and recorded as Hoshino, T. and Yukawa, H. 1977. Effect of ultrasonic waves on heat trans-

Permeate and retentate (concentration factor ca. 2x) from UF of skim milk were combined, and cream was added to produce skim milk (0.1% fat) and 1% milk with a range of true protein contents (1.0 to 4.8%) within each fat level. A panel that had been trained for descriptive sensory analysis evaluated the appearance, aroma, flavor, and textural attributes of milks. Relative viscosity and Hunter color values for whiteness (L value), greenness to redness (a value), and blueness to yellowness (b value) increased when either protein or fat was increased. The rate of change of L, a, and b values as protein content changed was greater for skim milk than for 1% milk and was greater as protein contents decreased. Sensory scores for several descriptors of appearance, texture, and flavor had a stronger positive correlation with objective measurements of whiteness than with objective measurements of viscosity. Thus, the judgment of panelists about milk texture and flavor in milks that differed in protein content was influenced more by appearance than by viscosity. As the protein content of skim and 1% milk was increased from 2.9 to 4.8% true protein, the sensory properties of the milks were made more like those of higher fat milk, particularly those of skim milk, mainly because of whiter appearance. Panelists perceived changes in the sensory characteristics of both skim and 1% fat milk when the true protein content was increased by 0.9%, the smallest increase that was studied in the experiment.