Abstract
Changes in several physicochemical properties related to the thermal denaturation of ovalbumin have been investigated at neutral pH and low ionic strength. The far-UV circular dichroism (CD) spectrum at 80°C indicated small secondary structural changes compared with those induced by addition of guanidine hydrochloride (GuHCl). The near-UV CD spectrum and difference absorption spectrum (250–320 nm) showed completely irreversible micro-environmental changes around the aromatic amino acid residues upon heat treatment (at ≥67°C). In the sedimentation measurements of heated ovalbumin solutions a sharp, single peak, corresponding to soluble aggregates of low polydispersity, appeared, and these aggregates were observed as linear polymers by transmission electron microscopy. After 2 h of heating at 75°C at pH 7.0, the intrinsic viscosity was ~20 times higher than the native one. We conclude that, under these conditions, although the globule form of ovalbumin molecule did not alter drastically upon thermal denaturation, partially denatured molecules which would expose the hydrophobic area(s) aggregate immediately and linear polymers (high-molecular-weight soluble aggregates) were formed.
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