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P. J. LUCK, E. A. Foegeding, and D. A. Clare. Dept. of Food Science, North Carolina State Univ., 238 Schuab Hall, Box 7624, Raleigh, NC 27695-7624 Recent dietary shifts have caused growing interest in high protein containing foods. High protein beverages are problematic due to protein aggregation caused by thermal processing. This problem has been addressed for whey protein beverages by adjusting pH and ionic strength or adding hydrocolloids. Roefs and De Kruif (1994) propose a kinetic model for heat-induced aggregation of b-lactoglobulin (b-lg), a whey protein, involving 3 steps: initiation, propagation and termination. By increasing redox potential of solutions containing b-lg, disulfide exchange reactions will be forced into favoring disulfide formation between b-lg monomers, naturally in the dimer state, and favoring termination reactions. Here conditions were altered to promote oxidation of sulfhydryl groups thereby favoring the termination step of b-lg polymerization and ultimately affecting protein aggregation. The effect of 1 to 5 mM CuSO4 and heat treatment at 60 or 80oC on pH 7.0 whey protein isolate (WPI) solutions was examined using native, non-reducing and reducing electrophoresis, free and total reactive cysteine measurement, and small strain oscillatory rheological measurement. WPI solutions containing no added CuSO4 heated to 80oC had high levels of large MW polymers as evidenced by non-reducing SDS-PAGE. Addition of 5 mM CuSO4 decreased large MW polymers, maintained a-lactalbumin monomers and increased b-lg dimers. CuSO4 addition and heat treatment decreased free and total reactive thiols indicating increased net disulfide bonding. Formation of small MW polymers by CuSO4 addition and heating created solutions that were liquid-like at 25oC as compared to fluid gels formed without CuSO4. These results suggest heat and oxidizing agents can be used to control WPI aggregation at neutral pH. Small MW disulfide bonded polymers can be formed and their solutions remain fluid at room temperature. Addition of CuSO4 to WPI solutions controls aggregation such that high protein levels can be heat processed with minimal formation of large aggregates.
Session 79, Food Chemistry: Protein and enzyme chemistry
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