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J. P. DAVIS and E. A. Foegeding. Dept. of Food Science, North Carolina State Univ., 200 Schaub Hall, Box 7624, Raleigh, NC 27695-7624 Soluble polymers of disulfide linked whey proteins, formed under proper heating and solution conditions, can provide foods with unique and improved functional properties. Optimal ratios of native whey protein isolate (WPI) and polymerized whey protein isolate (pWPI) have been determined for foam formation and stability; however pWPI effects on foam rheology are undetermined. This is unfortunate when considering food foams are often extensively processed after formation, meaning their successful manufacture is firmly tied to their rheological profiles. Our objective was to systematically measure the yield stress (t) of whipped foams consisting of WPI and pWPI, while simultaneously investigating the mechanisms responsible for this property. Foam t was determined via vane rheometry. Air phase volume (f) was determined via density measurements. Adsorption and dilatational rheological measurements at a model interface were determined via pendant drop tensiometry. Yield stress displayed a parabolic trend with increasing pWPI content, peaking at 50%. Equilibrium surface tension steadily increased and f steadily decreased with increasing pWPI content, consistent with the predictions of a theoretical equation describing foam t. Dynamic surface tension measurements revealed that native WPI adsorbed much more rapidly than pWPI, presumably due to the latter’s larger size. Interfacial dilatational elasticity (E¢) measurements displayed a parabolic trend with increasing pWPI content, peaking at 50%. This suggested that pWPI coadsorbs with native WPI, bolstering E¢ of native WPI interfaces. However, too much pWPI caused a weakening of the network. A positive, curvilinear relationship between E¢ and t was observed, consistent with that observed for WPI foams formed at various pH and salt ranges, suggesting a general link between these parameters. This study established that pWPI incorporation is a useful strategy for modifying foam t. A previously observed relationship between E¢ and t was confirmed, improving our capacity to design and seek ingredients which improve food foam rheology.
Session 64, Dairy Foods: Milk proteins
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