| Pidan is a traditional Chinese egg product, which possesses special taste and odor, and it is a very good appetizer to help digestion. Processing principles of preserved eggs are to transform the egg white and yolk from natural state to coagulation status by infiltration of NaOH. At present, the processing of preserved eggs industrially used commonly is solution soaking, which requires 35-40d preserved at room temperature. The elongation of Preserved egg production cycle bring about many problems, such as low production efficiency, unstable product quality and too heavy alkaline taste, limiting the further development of preserved eggs processing. The factors such as temperature and salted preserved eggs recipe were studied to shorten the production cycle and improve the production process. But it is very limited for the reduction of production recycle. A new process is in direct need to shorten the production cycle at the base of no impact on the quality of preserved eggs. Relevant research was carried out to study influence of the factor on the curing process. The main results are as following:Firstly, by setting three preserved NaOH concentration as 4%,5% and 6%, with a mixture of zinc and copper salt under the curing temperature of 22±2℃, the NaOH concentration of feed liquid, the contents of free alkalinity, water content, texture properties in eggs and other indicators were detected after curing for 0,4,7,12,18,25,30 days, respectively, and the corelation of alkali concentration in feed liquid and eggs was discussed, then through regression analysis with free alkalinity after the uniform design of the egg white, the inner and outer yolk, it is showed that the influence of number of pickling days on the free alkalinity of egg white is greater than the alkali concentration; the number of preserved days and the concentrations both have significant effect on the concentrations of free alkalinity in external yolk layer, also influence of the former one is elegant; the number of days affected the free alkalinity in inner salted egg yolk evidently, but the impact of alkali concentration was not such significant. The regression equations are:YA=-100+4.57×X(A)+ 50.0×X(B), YIY= 18.4+1.92×X(A)+ 4.00×X(B), YEY=-81.8+7.54×X(A)+17.5×X(B). The effect of different heat treatments on quality of pidan which were pickled by a zinc-copper salt was investigated. The L9(34) orthogonal test were used in this study and three factors of heat treatment as follows:heat time (15,20,25 d), heat duration (14,22, 30 h) and heat temperature (35,42,49℃). The moisture content, hardening rate, free alkalinity and color of pidan were used for the evaluating indicator.The results showed that heat treatments make pidan have lower moisture content, faster solidification, more hardening rate, lower free alkalinity, great color, and improved taste and favor. Analysis of variance from combination score of pidan’s hardening rate and free alkalinity obtained by fuzzy weighted transformation, showed that the degree of the influence factors decrease in the following order:heat time, heat temperature, heat duration, and the optimal processing condition was that samples were treated at the temperature of 42℃for 22 h after being preserved for 20 days. This method can short production cycle of pidan to 21 days, which is 40%-50% less than the traditional method.According to U10(108) uniform design, the fluctuating pressure curing technology is used to shorten the production cycle of preserved eggs. The process of pressure and pressure relief, which contribute to the maturation of preserved duck eggs, are controlled by pressure control program, with the infiltration of alkali into egg accelerated by high pressure and evolution of moisture, H2S, NH3 and CO2 outside promoted by the pressure difference between internal and exterior egg during low pressure process. The optimized process i.e. alkali concentration 5%, high pressure 180kPa kept 40min, low pressure 12min, pickled 206h, was selected after the comprehensive assessing the free alkalinity of preserved eggs white and inner-outer egg yolk, yolk cementation index and sense organ etc. The process used in this work could shorten production cycle to 78% of the traditional process, significantly improve production efficiency at the same time. The results showed that various factors on the quality of preserved eggs were significant(P <0.05), in order of influence degree is:length of preserved time> Low hold time> pressure hold time> preserved concentrations>the degree of high-pressure. The negative correlation exist between integrated quality and the value of pressure; With the definition of pickle time, low pressure distribution has an important role in the quality of preserved egg, which the influence of egg yolk low-pressure holding time on the inner yolk’s free alkalinity was the most significantly.With the view that the intermittent pressure can make the material liquid alkali material permeate rapidly into the duck egg white, increasing the free alkalinity of the preserved egg and causing egg white injury, the medium temperature treatment will be employed to investigate combination effect of this two kinds of technology. Concrete way is preserved eggs treated under the intermittent pressure in the tank, followed by optimal temperature 42℃treatment with various time. The free alkalinity, water content within preserved egg white and thickness of egg yolk and solidification hardening rate and other indicators were measured and analyzed assistant with sensory evaluation methods to select the best combination of intermittent pressure and medium temperature, i.e. alkali concentration of 4.00%, high pressure 190kPa, maintaining for 29.44min, maintaining for 17.22 min under low pressure, cured for 152h followed by 42℃heat treatment for 3 days. Production cycle is approximately 8.3d which is shorter than traditional process by 72-79%. Well solidified egg white and free alkalinity (224.74±0.33) mg/100g which is lower than traditional method by 25.86 mg/100g were obtained with this method. Also Songhua generated is large and a significant delamination exist from outer layer to the center layer, soft yolk is small, egg yolk hardening rate can reach 59.15%. The novel technology of combination of intermittent pressure and heat treatment has new epoch-making significance to process preserved eggs.The nutritional quality of preserved eggs treated with the new technology by measuring the general nutrients, amino acid composition and content, mineral content and other indicators, it’s found that the proportion of essential amino acids in cotreatment with intermittent pressure and media temperature treatment is 42.79%, which is higher than the control group by 2.31%; by the statistics of eggshell thickness and strength, bad eggs rate, there is no significant effect on egg shell. Finally, preserved eggs treated with the new process were stored at room temperature for 90d, and measure the weight loss, pH value and changes in the total number of colonies preserved eggs during storage, it’s discovered that three kinds of new technology treatment preserved egg have no deterioration phenomenon stored for 90d out of tanks, the total number of colonies were 486.15 cfu/g,372.96 cfu/g,353.18cfu/g, respectively,which were all in line with national standards standards. |
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