Ostwald ripening of protein-stabilized emulsions: effect of transglutaminase crosslinking

Ostwald ripening in n-alkane oil-in-water emulsions stabilized by sodium caseinate at neutral pH has been studied by monitoring time-dependent changes in the number-average droplet diameter and the droplet-size distribution. In qualitative agreement with theory, the destabilization rate has been shown to increase with reduction of the n-alkane chain length and on addition of ethanol to the aqueous phase. Replacement of caseinate by beta-lactoglobulin also leads to improved stability, but addition of calcium ions does not. The potential use of transglutaminase-induced crosslinking of adsorbed protein as a way of inhibiting the Ostwald ripening of caseinate-stabilized emulsions has been examined. It is shown that enzymic crosslinking before emulsification can lead to a modest reduction in the coarsening rate at long storage times. Crosslinking of caseinate after emulsification produces enhanced stability at short times, but there is a catastrophic loss of stability at long times due to droplet coalescence. (C) 1999 Elsevier Science B.V. All rights reserved.