Emulsions capacity

Emulsion Capacity is the property of the protein product solution or suspension to emulsify oil. The measurement is of the maximum amount of oil that the mixture will emulsify without losing its emulsion characteristics. The steps involved in this test are 1) Hydration - formation of the aqueous mixture. 2) Oil addition - with agitation the cause of emulsification. 3) Stress - a result of the heat generated during emulsification. 

Data in Table I show that emulsion capacity of peanut flour decreased with increasing flour or protein concentration while emulsion viscosity increased. This phenomenon was also demonstrated by McWatters and Holmes (2D. A decrease in flour particle size increased emulsion capacity and viscosity appreciably. Increasing the rate of mixing, however, decreased emulsion capacity but increased viscosity. Increased speeds produce greater shear rate, which decreases the size of the oil droplet thus, there is an increase in the surface area of the oil to be emulsified by the same amount of soluble protein (23, 24). 

Data in Figure 6 show the effect of varying the pH and sodium chloride concentration on emulsion capacity of peanut protein isolate. Shifting the pH to levels above or below the isoelectric point improved emulsion capacity of peanut protein isolate in O.IM or 0.2M NaCl. Similar trends were noted when distilled water was used as the continuous phase (data not.shown). At the 0.5M NaCl concentration, however, little difference was noted in emulsion capacity at pH 3, 4, or 5 appreciable increases occurred when the pH was raised to 6 and above. At the highest salt concentration (1.OM NaCl), a gradual increase in emulsion capacity occurred when the pH was increased from 3 to 10. An overall suppression in emulsion capacity occurred as salt concentration increased except at pH 5 and 6. These emulsion-capacity curves closely resemble the protein-solubility curves of peanut protein shown in Figure 7... 

Attention has been directed toward modifying functional properties of peanut proteins by chemical, enzymatic, and physical approaches. Chemical modification has included acetylation and succinylation treatments (28, 29). Marked improvement in emulsion capacity occurred as a result of this treatment if the proteins were extracted in acid 28). Beuchat et al. 

Pea and Bean Seeds. McWatters and Cherry ( ) investigated the influence of pH adjustment on emulsion capacity and viscosity of cowpea flour (24.2% protein, dry wt basis) using the procedure of Carpenter and Saffle (23). Data in Table II show that adjusting the pH from the naturaT level of 6.4 to 4.0 reduced emulsion capacity by about 20% adjusting the pH from the natural level to... 

Table II. Effect of pH adjustment on emulsion capacity (EC) and viscosity of cowpea flour.

Sunflower Seed. Emulsion capacity of defatted sunflower meal was investigated by Huffman et al. (45) at three pH levels (5.2, 7.0, 10.8), blender speeds (4500, 6500, 9000 rpm), and oil addition rates (30, 45, 60 ml/min). With low mixing speeds and rapid rates of oil addition, optimum emulsion capacity occurred at pH 7.0. These authors related the observed emulsification properties to protein solubility, surface area and size of oil droplets, and rate of protein film formation. 

Lin et al. ( 6) measured the emulsion capacity of defatted sunflower seed products. Data in Table VII show that sunflower flour was superior in emulsifying capacity to all other products tested. The emulsions were in the form of fine foams and were stable during subsequent heat treatments. The diffusion-extraction processes employed to remove phenolic compounds dramatically reduced emulsion capacity, although isolating the protein improved emulsion capacity to some extent. 

Rapeseed. Methods employed in processing of rapeseed protein products influence emulsion capacities (48, 49). Kodagoda et al. (48) showed that rapeseed protein isolates from water extracts emulsified more oil than isolates from acid or alkali extracts (Table VIII). Rapeseed isolates emulsified more oil than their concentrate counterparts. Rapeseed isolates and concentrates from acid extracts were far superior in emulsion stability to rapeseed protein products from water or alkali extracts. 

Table VII. Emulsion capacity of defatted sunflower seed products.

Table IX. Emulsion capacity of rapeseed protein products.

Cottonseed. Emulsion capacity and viscosity characteristics of glandless cottonseed flour dispersed in water are markedly influenced by variations in pH and flour concentration (51,... 

Figure 10). Emulsion capacity was lowest near the isoelectric pH...

Kuehler and Stine (43) studied the functional properties of whey protein with respect to emulsifying capacity as affected by treatment with three proteolytic enzymes. Two microbial proteases and pepsin were examined. The emulsion capacity decreased as proteolysis continued, suggesting that there is an optimum mean molecular size of the whey proteins contributing to emulsification. 

McWatters and Holmes ( ) developed multiple regression models of the effects of pH and salt concentration on functional properties of soy flour. Design of the experiment and selection of the factors to be Included were based. In part, on earlier findings that emulsion capacity of defatted peanut meal was Inhibited around the Isoelectric point (ca pH 4.0)... 

There are a number of key points to be made about the variables used In the equations. First, the equation forms used for the high salt concentration (1.0 M NaCl) are simple quadratic and cubic forms using pH and the square and cube of pH as Independent variables. The high salt concentration negated the emulsion Inhibiting effects of the Isoelectric point. The percent of the variation In the function properties accounted for by these equations ranged from about 80 percent for emulsion viscosity to over 98 percent for emulsion capacity. 

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