Changes in chemical composition, physical properties and microstructure of duck egg as influenced by salting

Abstract

Changes in chemical composition, physical properties and microstructure of duck egg, during salting for up to 14 days, were determined. Duck egg consisted of 10.87% shell, 54.73% egg white and 33.94% yolk. Salting resulted in an increase in weight proportion of egg white, but a decrease in yolk proportion. Moisture contents of both egg white and yolk decreased gradually with concomitant increases in salt and ash contents as the salting time increased. Protein and lipid contents increased slightly in both interior (viscous portion) and exterior (hardened portion) egg yolk with increasing salting time. Oil exudation was observed in yolk, particularly in exterior yolk. Triacylglycerols and phospholipid, found as the major lipids in egg yolk, underwent slight changes, but no differences in protein patterns of either egg white or egg yolk were observed during salting. Hardening ratio and hardness of egg yolk increased with increasing salting time. Adhesiveness and gumminess also increased, while springiness, cohesiveness and gumminess decreased slightly when the salting time increased. Scanning electron microscopic study revealed that yolk granule was polyhedral in shape and aligned closely when the salting proceeded. Protein spheres were distributed uniformly, together with oil droplets, in salted yolk, as visualised by transmission electron microscopy. Confocal laser scanning microscope (CLSM) micrographs indicated that the greater dehydration and release of lipids took place in egg yolk during salting.