Peanut emulsion capacity

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. 

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)... 

Figure 6. Effect of pH and suspension medium on the emulsion capacity of peanut proteins. Suspension medium (0—0 ) H30, (O----O) 0.1M NaCl, (0---Q)...

Lin et al. (15) showed that sunflower meal was superior to soybean and sunflower concentrates or isolates In emulsion capacity. McWatters and Cherry (9) compared select functional properties of defatted soybean, peanut, field pea, and pecan flours and showed that major seed storage proteins were important in emulsifying and foaming properties. Protein solubility was related to the quality of the emulsions and foams. Behavioral characteristics contributed by nonprotein components that occur naturally In the seeds, especially carbohydrates, were Implicated. 

Emulsion Capacity. Enzymatic digestion of proteins beyond 10 min, except the trypsin-treated sample for 30 min, destroyed emulsifying capacity of the flour (Figure 13). Apparently, hydrolysis substantially altered protein surface activity strengths and the ability of the protein to stabilize oil-in-water emulsions. This assumption agrees with earlier work showing decreased emulsion capacity of peanut flour fermented with fungi (27). 

Bnulsion Capacity. The most viscous emulsions of peanut meal with mayonnaise consistencies were produced from suspensions at pH 1.5 in water and 0.1 M NaCl, and by the water suspension adjusted from pH 6.7 to 4.0 to 8.2 (Figure 6). At pH 4.0, poor emulsifying properties were noted for all suspensions. The two-step pH adjustment from 6.7 to 4.0 to 6.7 improved emulsification properties of only the water suspension over those of samples where the pH was not adjusted or was minor. 

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