关键词: 鸡蛋壳, 鸭蛋壳, 力学特性, 超微结构, 蛋壳组分

Abstract:

【Objective】The research was conducted to study the comparison of shell mechanical property, ultrastructure and component between chicken and duck eggs. 【Method】160 eggs at the average weight from laying hens (Hy-Line grey) or ducks (Longyan Shanma) in aged 45 weeks were randomly divided into 2 groups, respectively. Each group had 20 eggs with 8 replicates. The laying hens and ducks were fed with maize-soybean meal basal diet, and the nutritional levels were formulated according to the national standard. The eggshell strength was measured by eggshell strength analyzer, the thickness of eggshell membrane and calcified eggshell was measured by digital micrometer, and then the eggshell ratio and toughness were calculated. Scanning electron microscope (SEM) was used to observe the ultrastructure of eggshell and to measure the effective thickness, mammillary thickness and width, and then to calculate the total thickness, the ratio of effective or mammillary thickness relative to total thickness. The mammillary structure was also observed by SEM and the degree of variation was scored. After crushing and extracting the eggshell, the content of matrix protein was determined by Coomassie brilliant blue method. After microwave digestion, the content of calcium, phosphorus, magnesium, manganese, copper and zinc in eggshell were determined according to the national standard method. 【Result】In comparison with chicken eggshell, the weight of duck egg and eggshell were increased (P<0.01), but the shell ratio was not changed (P>0.05); the eggshell breaking strength, toughness and eggshell membrane thickness were increased (P<0.01), but the thickness of the calcified eggshell (without shell membrane) was not changed (P>0.05). In respect to the ultrastructure, the thickness of mammillary layer and the number of mammillary knobs in per unit were decreased, but the mammillary knob width and mammillary layer ratio in duck eggshell were increased in relative to those of chicken eggs (P<0.001). No differences were observed in total and effective thickness (P>0.05), but the ratio of effective layer relative to total thickness was increased in duck eggshell (P<0.001). About the ultrastructure of mammillary knobs, there were no significant differences in the mammillae density, type B, type A, aragonite, cuff and pitted structure scores of the duck eggshell (P>0.05), the scores of the variations such as caps, early fusion and late fusion, and the total score of knobs were decreased in duck eggshell compared with chicken eggshell (P<0.05). There was higher frequency of mammillary structure variation in the chicken eggshell than the duck eggshell. The groove-like traces on the cap structure of the duck eggshell were deeper and clearer, the early fusion was more extensive, and the bonding between the knobs and the shell membrane fibers were denser than that in chicken eggshell. The contents of phosphorus, copper and manganese in duck eggshell were increased (P < 0.05), but the magnesium and matrix protein contents were decreased in duck eggshells relative to those in chicken eggshell (P<0.001), and there were no significant differences in calcium and zinc content (P>0.05). 【Conclusion】Above all, the eggshell quality of chicken and duck eggs were similar, and there were no differences in eggshell ratio, thickness of calcified layer, calcium and zinc content in eggshells. Compared with the chicken eggshell, the mechanical properties of duck eggshell were better, for shell breaking strength and toughness of duck eggshell were increased, which mainly due to the improvement of shell ultrastructure by increasing effective thickness and the ameliorate of mammillary knobs in duck eggshell. In addition, the phosphorus, copper and manganese content in duck eggshell were increased, but the content of magnesium and matrix proteins were decreased. In some content, the quality of duck eggshell could be improved by regulating the mineral elements and matrix protein content in eggshell, and modulated the process of eggshell formation, especially the deposition of calcium carbonate in the mammillary and palisade layers, and increased effective thickness and improved structure of the mammillary layer.

Key words: chicken eggshell, duck eggshell, mechanical properties, ultrastructure, eggshell components