Effect of olive leaf water extract on physical properties of egg white meringue

Abstract

Olive leaf cold-water extract (OEx), which has cross-linking activity of protein molecules, modifies the physical properties of heat-induced chicken egg white gel. In this study, we investigated the effect of OEx in the range of 0.1 to 1.0% (w/w egg white) on the physical properties of egg white meringue. The overrun of meringue prepared from egg white decreased with increasing amount of OEx. For meringue baked at 121ºC, the specific volume of baked meringues with 0.1 and 0.5% OEx tended higher than that of OEx-free counterpart. Baked meringue with 0.5% OEx had 1.3 times higher breaking stress than that without OEx. On the other hand, for meringue baked at 93ºC, baked meringue with 0.5% OEx had 1.6 and 1.9 times higher breaking stress and breaking strain than OEx-free meringue, respectively. Scanning electron observation showed that the addition of 0.5% OEx to egg white induced denser microstructure of baked meringue. The contents of primary amino group and SH group in egg white protein decreased with increasing addition of OEx, contrarily the cross-linkage formation between protein molecules enhanced. It is presumed that the chemical changes, that is protein cross-linkage etc, link to the denser microstructure in baked meringue; resulting in the modification of the physical properties. The present study suggests that OEx is feasible to improve the texture of meringue-based confectioneries.