| Pidan also known as hundred-year egg, is one of the most traditional and popular preserved egg products in China. But in the traditional process, lead residues and high copper residues restrict the consumption and export of pidan. Combining the actual effect of pidan, content of sodium hydroxide in the pickling solution, pH value and texture profile analysis of pidan made by different copper, zinc, iron, manganese salts during pickling were analysed in this paper. Meanwhile, optimal metal salts which could bring best quality to pidan were selected. Moreover, a new curing agent was developed. Chemical composition, physical properties and microstructure of pidan treated with copper sulfate, zinc sulfate and the new curing agent also were analysed. The results shows as below:The actual effects of pidan made by different metal salts were different. Copper chloride and copper sulfate were optimal for pidan making. Copper gluconate could not be used to make pidan. Meanwhile, The effects of pidan treated with zinc lactate, zinc acetate were good, they were also good in the treatments of zinc sulfate and zinc chloride, but a little spicy. Zinc gluconate and zinc oxide were not optimal for pidan making. Iron and manganese salts could not be used to make pidan too. There were black spots on the shell surface of pidan made by copper salts but zinc salts, moreover the processing period was 35 day in copper treatments and 25 day in zinc treatments.The variation tendency of sodium hydroxide content in the pickling solution containing different metal salts was different. It increased quickly at the beginning of pickling(P<0.05) in the treatments of copper, zinc, iron, manganese salts, that changed slowly at the late stage of pickling(P>0.05). The decreasing rates of sodium hydroxide at the late stage(15-25 d) were different in different metal salts treatments. It fell 0.01%-0.13%in copper treatment,0.05%-0.24%in zinc treatment,0.11%-0.19%in iron treatment and 0.14%-0.33% in manganese treatment. Generally, the variation tendency of sodium hydroxide in pickling solution treated with different compounds which had same metal element was similar.The variation tendency of pH value in pidan made by different metal salts was different. It increased quickly at the beginning(0-15 d) of pickling(P<0.05) and changed slowly at the late stage(15-35 d) of pickling(P>0.05). In zinc treatments, the pH value of pidan with zinc gluconate, zinc acetate and zinc oxide changed quickly during pickling. It also increased quickly at the beginning of pickling(P<0.05) and changed slowly at the late stage(20-25 d) of pickling(P>0.05) in iron treatments. It increased and then decreased and changed quickly(P<0.05) in the manganese treatments but manganese sulfate in which it changed slowly at the late stage of pickling (P>0.05). The final pH was 9.9-10.2,10.16-10.35,10.91-11.03 and 10.52-11.26 in copper, zinc, iron and manganese treatments respectively. Generally, the variation tendency of pH value of pidan treated with different compounds which had same metal element was similar.The variation tendency of texture profile analysis on pidan white made by different metal salts was different. In copper chloride and copper sulfate treatments, the hardness and springiness of pidan white increased quickly at the beginning of pickling and changed slowly at the late stage of pickling. They increased as the pickling time expanding but the value was low in the treatment of copper acetate. They increased and then decreased quickly in the treatment of copper gluconate. The hardness and springiness of pidan white also increased quickly at the beginning of pickling and changed slowly at the late stage of pickling with the zinc sulfate, zinc chloride, zinc lactate and zinc acetate. They are decreased quickly with the zinc oxide. The pidan white gel liquefied in the treatments of iron and manganese after day 15 of pickling.The variation tendency of texture profile analysis on pidan yolk made by different metal salts was different. The hardness of pidan yolk with copper salts increased as the pickling time expanding and the adhesiveness increased and then decreased, after that, it changed slowly. The hardness of pidan yolk with zinc sulfate, zinc chloride, zinc lactate, zinc acetate and zinc gluconate increased as the pickling time expanding. It decreased at the late stage of pickling with the treatment of zinc oxide. The hardness and adhesiveness of pidan yolk alao increased and then decreased in tne treatment of iron salts, the adhesiveness decreased quickly. They had similar variation tendency between the treatments of iron and manganese salts but manganese sulfate in which the hardness was low and increased as the pickling time expanding.Using orthogonal design method, the curing agent formulation was optimized by multi-factor, multi-level, multi-index of fuzzy linear transformation design method. Based on the comprehensive analysis, optimal component was determined. The best formula (conversion for quality score) is like this:33.3% zinc sulfate,16.7% copper sulfate,33.3% ferrous sulfate,16.7% zinc chloride, the total addition of the formula is 0.3% of the pickling solution mass. The cost of production fell 21.58%, process period shrunk by up to 43%, the content of copper element of pidan fell 29.7% using thie formula to make pidan. It could be as a useful reference for pidan industrialized production.Chemical composition, physical properties and microstructure of pidan treated with copper sulfate, zinc sulfate and the new curing agent were different. The pH value of pidan white and yolk was copper sulfate (B)< new curing agent (C)< zinc sulfate (A)(P<0.05). The moisture contents of pidan white and yolk in A and C were similar which were lower than that with B(P<0.05). The ash content of pidan white in B and C differed slightly(P>0.05) which was lower than that with A(P<0.05). The ash content of pidan yolk, protein content of pidan white and lipid content of pidan yolk differed slightly(P>0.05) in the three different treatments. Fatty acid composition was similar in all treatments. The springiness of pidan white and the hardness, adhesiveness of pidan yolk differed slightly(P>0.05) in all treatments. The hardness of pidan white in C was higher than another two treatments (P<0.05). The metal content of pidan increased if it was added into pickling solution. Pidan white and yolk of different treatments visualized by SEM, smoother surface of pidan white gel and smaller size of polyhedral granules are observed in pidan treated with B and C. The size of granules with B and C was 30-80μm, it was 50-100μm in the treatment of A. |
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