80-3 |
Ultra high pressure: Molten globule structure and hydrophobicity of b-lactoglobulin |
B. G. SWANSON1, J. Yang1, J. R. Powers1, S. Clark1, and A. K. Dunker2. (1) Dept. of Food Science & Human Nutrition, Washington State Univ., PO Box 646376, Pullman, WA 99164-6376, (2) School of Molecular Biosciences, Washington State Univ., 638 Fulmer, Pullman, WA 99164-4660 Ultra high pressure (UHP) is an easily adapted technology that can be uniformly applied to foods or food constituents to improve quality and functionality. UHP will depolymerize protein oligomers and unfold protein monomers. However, the mechanisms underlying pressure-induced protein unfolding is controversial. b-lactoglobulin (b-LG) contributes diverse functional properties such as solubility, gelation, foaming, emulsification and flavor binding to foods. Investigation of high pressure induction of changes in the structure and functionality of b-LG will provide useful insights for the potential use of whey proteins in formulated food products. b-LG treated with UHP at 600 MPa, pH 7.0 and 50°C exhibits increased intrinsic tryptophan fluorescence and a 3-fold increase in extrinsic 1-anilino-naphthalene-8-sulfonate (ANS) fluorescence. Far ultraviolet circular dichroism (CD) spectra reveals that b-LG retains secondary structure following UHP treatment. Near ultraviolet CD spectra reveals that the native tertiary structure of b-LG essentially disappears after UHP treatment. Urea titrations reveal that UHP treated b-LG unfolds non-cooperatively and is stable for 3 months at 5°C. The free thiol group of cysteine121 in native b-LG becomes accessible and forms S-S linked b-LG dimers during UHP treatment. UHP treatment induces b-LG into an intermediate protein structure identified as the molten globule state stabilized by disulfide bonds. Native b-LG binds retinol in the calyx and cis-parinaric acid (CPA) at the surface hydrophobic site. Conformational changes in the calyx and surface hydrophobic sites of b-LG during UHP treatment result in decreased retinol and CPA fluorescence. b-LG in the UHP induced molten globule state exhibits decreased affinity for capsaicin, palmitic acid and carvacrol. The unique hydrophobic affinity of b-LG in the UHP induced molten globule state may result in potential improvement of ingredient functionality and food quality.
Session 80, Ultra high pressure: Molecular changes in foods
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