The Analysis Of The Spot On The Surface Of Preserved Egg And The Study Of The Method To Control It

Preserved egg is a traditional egg product in China. Currently, the research and report of composition of the black spots on the surface of preserved eggs is less. With the development of detection technology, the combine use of equipment can provide a more effective way for the component analysis of the unknown substance. In this paper, with the combine use of scanning electron microscopy spectrum (SEM-DES), photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) techniques and other instruments, a preliminary analysis of chemical structure of the spots on the commercial preserved eggs surface is studied. For the elements, the black spots area on the eggshell of preserved eggs not only detect conventional elements,but also detect copper (Cu) element, however the no spots parts and duck eggshell can not detecte the presence of Cu. For the valence, the characteristic peaks spectrum of the valence is close to the peak spectrum of the divalent copper in the photoelectron spectra energy spectra, which both have a bulge crystal spore peak, it can be speculated that the price of copper of the spots is in divalent state. For the crystal structure, the characteristic diffraction peaks spectrum is the similar with the copper sulfide (CuS) in the JCPDS standard card, of which the main peak at 2T=29.652, 48.714,58.282 is consistent with the characteristic diffraction peaks of CuS. In addition, the copper content of spotted eggshell were measured by Atomic Absorption (AAS) and Inductively Coupled Photoelectron spectroscopy (ICP-AES), and the copper content is up to 700μg/g, which is significantly higher than those eggshell without spots and the duck eggshell. Based on the two above aspects of qualitative and quantitative conclusions, it can be initially speculated that the composition of surface spots on preserved eggs is copper sulfide.In the case that kowning the chemical composition of the spots in the surface of preserved eggs, the reaserch continue to study the effect of different raw materials to the formation of spots on the surface of preserved eggs. Based on machine vision methods, the overall color characteristics of the spots of preserved eggs is available through the image acquisition system. Using computer software to quantify the spots and obtained the brightness values of the eggshell, in order to examine the types and concentration of metallic additives, the concentration of sodium hydroxide and salt how to affect the formation of spots of preserved eggs. The results showed that when using zinc as additive has the highest brightness value, which is 198.27, and there almost are no black spots on the surface. However, when using the copper and lead as additives, the brightness value of eggshell become low and the spots increased on the surface with the concentration increasing of metal ions.When the sodium hydroxide concentration is 5.0%, the eggshell has the highest brightness, which is 190.37, and has the least spots on the surface of preserved eggs. When the sodium chloride concentration is 3.0%, the eggshell has the highest brightness, which is 189.96, and has the least spots on the surface of preserved eggs. Through L9 (33) orthogonal test and the weighted score on the test results (sensory take 60% in proportion, the value of the shell brightness take 40% in proportion), the results show that the order of factors affect the comprehensive quality of the preserved eggs is:Concentration of salt>Concentration of sodium hydroxide> Concentrations of metal. The best preserved ratio is:sodium hydroxide 6% in weight proportion, salt 2% in weight proportion, copper chloride 0.3% in weight proportion.Have studied the effect of raw materials to the formation of spots, it continues to study the influence of curing process to the formation of spots of preserved in this paper. It has studied the effects of different feeding methods, curing temperature and numbers of curing days to the formation of spots, respectively. It can conclude that useing the mother liquor methord is more effective than the direct addition method to reduce the formation of spots.With the curing temperature and curing time increasing, the brightness value of the shell decreased and the spots increased significantly. Through orthogonal test L9 (33) and the weighted score on the test results (sensory take 60% in proportion, the value of the shell brightness take 40% in proportion), the results show that the order of factors affect the comprehensive quality of the preserved eggs is:curing temperature> the number of curing days> salt concentration. When the salt concentration take in 2%, curing temperature at 20℃for 30 days, the preserved eggs not only have fewer spots on the eggshell surface, but also have higher sensory score.Finally, it can be found that the best preserved group has fewer spots on the surface of preserved eggs than other preserved groups and commercial groups, meanwhile the taste and other sensory indicators is better and the comprehensive quality has been improve, by comparing different groups of spots on the surface of preserved groups and commercial groups, as well as the internal quality,which include the sensory quality, hardness, cohesiveness, cohesion, chewiness and resilience, pH, total alkalinity, free alkalinity, volatile basic nitrogen and heavy metals of protein and yolk of the eggs.