Characteristics of glycosaminoglycans in chicken eggshells and the influence of disaccharide composition on eggshell properties.

Glycosaminoglycans (GAG) are linear, highly negatively charged polysaccharides that may perform an important role in biomineralization. GAG were isolated from chicken eggshell membranes and calcified shells. Disaccharide compositional analysis was performed using liquid chromatography-mass spectrometry. All 4 groups of GAG - hyaluronan (HA), keratan sulfate (KS), chondroitin sulfate (CS), and heparan sulfate (HS) - were detected in shell membranes and in calcified shells. HA was the most plentiful GAG in shell membranes, and CS was the most abundant in calcified shells. The CS present, in both membranes and calcified shells, consisted primarily of 6SCS-C, 4SCS-A, and 0SCS-0 disaccharides. Neither 4S6SCS-E nor 2SCS was detectable in shell components. Small amounts of 2S4SCS-B were detected in membranes and TriSCS, and 2S4SCS-B and 2S6SCS-D were detected in calcified shells. HS in calcified shells contained all disaccharides except for 2S6S. In shell membranes, HS contained primarily NS and 0S as well as small amounts of TriS, NS2S, NS6SHS, and 6S, but neither 2S6S nor 2S was detectable. The disaccharide composition of membrane CS, as well as membrane and calcified shell HS, were very similar in all eggshells. In contrast, the composition of calcified shell CS disaccharides was highly variable. In membranes, both HA and KS content showed a correlation with egg shape index. The 4SCS-A content correlated with eggshell strength, and 0SCS-0 correlated with eggshell strength and calcified shell thickness. HS content and its disaccharide composition showed no apparent correlation to properties of calcified shells. In calcified shells, only HS 6S correlated with egg shape index. This study suggests that GAG content and disaccharide composition of shell membranes might impact the quality of chicken eggshells.