The Change Of Lipid Of Preserved Egg Yolk During Pickled By Vacuum Technology

Preserved egg is one of Chinese traditional egg products with rich nutrition, it is convenient for consumption, and welcome by domestic and foreign consumers. In recent years, many scholars research the formation mechanism of preserved eggs.The objectives of present work based on the laboratory conclusion before. The conditions of preserved egg pickled by the methods of vacuum technology as follows, the temperature was 23 ℃, the vaccum degree was -0.08～-0.1 MPa. Under these conditions, the preserved eggs would be developed just for 6 days and ripend for another 30 days in thermostat at 25℃.Samples of preserved eggs pickled for 1-6 days were taken and frozen for 24h at-20℃, then separated the egg yolk, from the core to the outer offset was divided into 3 layers, the physicochemical indexes in different layers were measured. The results showed that, in the process of pickling, pH, zinc content, ash content, salt content rised ceaselessly, the moisture content increased first and then decreased. After curing, pH, ash content, salt content, zinc content of the outer layer were significantly higher than that of the middle and the inner layer and, and the moisture content was significantly lower than that of the inner layer and the middle layer of egg yolk. Total fat of egg yolk declined little, cholesterol and lecithin content of egg yolk reduced a lot(25% and 19.1%). Free fatty acid content showed a rising trend, about 22% increase.Samples were used to analyze the changes of lipases activity and phospholipase activity, the activities of lipase and phospholipase decreased in the pickling process. The effects of main influencing factors on the activities of lipase and phospholipase were studied using the orthogonal analysis method, pH and salt content was the main factors. Fat oxidation started from the maturity period, carbonyl value and conjugated diene value was higher in the ripening period (0.112U/min.g protein), correlation analysis result showed that enzyme activity could explain about 20% of the actual level of fat oxidation, indicated that lipoxygenase play a leading role in fat oxidation.Flavor compounds in egg yolk were extracted and identified by solid phase microextraction(SPME) combined with gas chromatography mass spectrometry (GC/MS) The flavor substances in egg yolk including alkyl alkenes, aldehydes, ketones, alcohols, esters, acids, aromatic, and heterocyclic oxygen, nitrogen heterocyclic. Relative content of alcohols, acids and esters barely changed, the relative content of ketones reduced, relative content of aldehydes, aromatic, alkane increased. Principal component analysis showed that the first principal component was mainly composed of straight chain aldehydes, which originated from lipid.Tea can lower the cholesterol content in egg yolk, the reduction range can be 28.5%. Considering the egg quality, cost, and cholesterol lowering effect,20g/kg is the best level of low cholesterol preserved egg production.