Chemical Composition And Physical Structure Of Eggshells With Distinct Eggshell Quality Or From Various Aging Hens

We studied the mechanical properties and chemical composition of eggshell from Xue-Shan henswith different age（s26weeks,40weeks and64weeks）, and further studied the chemical composition ineggshell and microstructure of eggshell between the normal eggs and sand cover eggs. The propose ofthe study is to reveal the regularity in the mechanical properties and chemical composition of eggshelllaid by hens with different ages, and the laws in the chemical composition and microstructure ofeggshell with various strength or eggshell between the normal eggs and the sand cover eggs, tosystematically explore the impact of the age of hens on eggshell quality and its physical and chemicalproperties, and establish the relationship between eggshell texture and eggshell physical and chemicalproperties to provide the basis for the regulation mechanism of the further study on eggshell quality.1) Eggshell mechanical properties were measured and analyzed. The results showed that the age ofhens have significantly (p<0.05) impacts on egg weight, eggshell relative weight, eggshell strength, eggshape index, but no impact on eggshell thickness. There are highly significant differences (p <0.01) inegg weight, eggshell relative weight and eggshell strength between the sand cover eggs and normal eggs,while other indicators had no significant differences (p>0.05).2) Using the atomic absorption spectrometer (ASS) and inductively coupled plasma massspectrometer (ICP-MS) to analyze the contents of the mineral elements in eggshell of eggs laid by hensduring different ages and those showed different quality，the results indicate that among the normaleggs from different weeks old layers, there is no different in the concentrations of Na, Ba, Cr, Rb, Co,Ga (p>0.05) in the eggshells, but the differences are significant or very significant (p<0.05or0.01) inthe concentrations of Ca, K, Mg, V, Li, Se, As, Cd, Cu, Sr, Ni, Mn. Furthermore, as the age of layinghens increasing, the content of Ca, K, V, Li, As, Se, Cd, Cu is decreasing, respectively; on the contrary,the content of Mg, Sr, Ni is increasing, respectively. Secondly, comparing the mineral contents ofeggshell of the normal eggs and the sand cover eggs, there are significant or highly significantdifferences in other elements (p<0.05or0.01) except Mg, Cr, Li, Rb, Ga, V(p>0.05). Thirdly, theeggshell strength has great significant positive correlation(p<0.01) with eggshell thickness and thecontent of K, Se, As, Cd in eggshell, has significantly positive relation(p<0.05) with Ga, and has a verysignificant negative correlation(p<0.01) with Na, Fe, Co, Ni, Se. In addition, there is a very significantpositive correlation (p<0.01) between the eggshell thickness and the contents of K in eggshell, and avery significant negative correlation (p<0.01). with the content of Na. Fourthly, the correlation analysisshows a complex relationship between the various mineral elements in the eggshell, for example, Ca, Khave a greatly significant negative relativity (p<0.01) with Fe, Ni, but have a greatly significant positivecorrelation (p<0.01) with As, Cd; Ga, Ba have a very significant negative correlation (p<0.01) with Na,but have a greatly significant positive correlation (p<0.01) with Mg.3) The ignition method at high temperature was used to analyze the contents of crude ash ineggshell from different weeks old layers, from the normal eggs and the sand cover eggs, and eggshellwith various strength. The results show that after removal of the shell membrane, the inorganic contents in the normal eggshell laid by three layers of different weeks old has no significant difference (p>0.05),with an average content of97.7%, accordingly, there is no significant difference between the organiccontent (p>0.05). However, the inorganic contents in the normal eggshell is significantly higher thansand cover eggshell (p<0.01), correspondingly, the organic content is less than the sandy eggshell andthere is very significant differences (p <0.01).4) Using scanning electron microscopy to study the ultrastructure of eggshell with differentstrength and texture, the observation shows that the milk cones in mastoid particles of eggshell withhigh strength and the normal eggshell have closely connected and regularly arranged. Whereas, themastoid layer of eggshell with low strength and the sand cover eggshell have a lot and large gap, themastoid individual connection loose and with irregular arrangement, the palisade layer arranged withlower regularly, the cracked line of the cuticle much more and out of flatness. Secondly, compared withthe normal eggshell, cuticle and vertical crystal layer of the eggshell with sand covering was uneven,like cauliflower, while the normal eggshell of the sand cover eggs has the similar ultrastructurecharacters with the normal eggshell.5) The usage of X-ray diffraction (XRD) to study the characteristics of the calcite crystals ineggshell with different texture, the results show that the calcite crystals in eggshell covered by sandgrow in the direction of more than one crystal face, but it have a (104) plane preferential growth in thenormal eggshell and the normal eggshell of the sand cover eggs. While, the normal eggshell and thenormal eggshell of the sand cover eggs have less diffraction peaks than the eggshell covered by sand,higher F factor of (10l) crystal face in the outer surface, but have the similar F factor of (10l) crystalface in the inner surface. However, F factor of (10l) crystal face in the outer surface of eggshell isobviously higher than the inner surface (except the eggshell with sand cover). The crystal grains in theinner surface of normal eggs are much larger than ones in the outer surface, but in the eggshell withsand cover, both crystal grains in inner or outer surfaces are nearly the same size.