Heating white sauce with bovine serum albumin (BSA) at 90 degreesC caused the sauce to separate into aggregates and liquid phase, although this did not occur at 75 degreesC. Data from differential scanning calorimetry of BSA solution suggested that heat denaturation of BSA was insufficient at 75 degreesC but was complete at about 90 degreesC. Larger aggregates of BSA were formed by heating at 90 degreesC compared with 75 degreesC, as shown by gel permeation chromatography combined with a multi-angle laser light-scattering detector. Dynamic viscoelasticity measurement showed a higher storage modulus of BSA solution formed by heating at 90 degreesC than at 75 degreesC. Scanning electron microscopy revealed a random agglomerate structure of aggregates (spherical aggregates) obtained by 75 degreesC heating, while a well-developed network structure containing voids was observed after heating at 90 degreesC. These findings suggest that sauce liquid separation induced by heating at 90 degreesC is due to encapsulation and restriction of white sauce components by large structured aggregates of BSA containing voids. Aggregates generated at 75 degreesC were not sufficiently developed and structured; therefore there was no sauce liquid separation due to encapsulation and restriction of components. (C) 2000 Society of Chemical Industry.