| The water-diluted method assisted by freeze-thaw treatment is a promising new technique for the extraction of immunoglobulin(Ig Y)from egg yolk.However,freeze-thaw egg yolk pellet(FYP)is produced as by-product in the process of extraction inevitably.FYP still contained many nutritional components,such as protein and essential fatty acids.However,few studies has been put on it.Therefore,this study uses FYP as raw material to prepare low-fat egg yolk powder(LF-EYP)and egg yolk oil(EYO)and study properties of them,so as to make comprehensive utilization of egg yolk resources.The following is the main research content of the paper.Firstly,FYP was modified by limited enzymatic hydrolysis technology.Hydrolyzed egg yolk pellet powder(HYP)was obtained by spray-drying method in order to effectively improve the functional properties of FYP.The results showed that the solubility and emulsifying stability of HYP significantly increased with the increase of enzyme addition level.In general,when the enzyme addition amount is 1000 U/g,the functional properties of FYP can be effectively improved.HYP prepared under this condition owes desirable solubility and emulsification,and has the potential of application in food industry.Secondly,in order to reduce the lipid content in HYP and make it accord with the modern low-fat and healthy diet concept,in this study,subcritical extraction technology was further used to extract oil in HYP to obtain low fat egg yolk powder with good functional characteristics and egg yolk oil.Propane was selected as the subcritical extraction solvent.The optimal extraction conditions were as follows: extraction temperature: 35℃,extraction pressure: 1.5 MPa,extraction time: 120 min,solid-liquid ratio: 1: 7(g/m L).Under this optimal condition,the residual oil rates of HYP with 250,500,1000 and 2000 U/g were 23.25%,19.25%,15.50% and 20.23%.Meanwhile,our study also found that enzymatic hydrolysis could not only modify the protein,but also improve the efficiency of subcritical extraction.Thirdly,for the purpose of evaluating the quality of LF-EYP obtained by subcritical extraction,the particle size distribution,microstructure and functional properties were further analyzed.The results showed that the particles of low fat yolk powder decreased and the structural damage became more severe with the increase of enzyme addition level.The solubility of Low-fat egg yolk powder was highest(90 g/100g)under 1000 U/g,but decreased when the enzyme addition amount was 2000 U/g.In addition,under the same addition amount of enzyme,emulsifying activity index and emulsification stability of low-fat egg yolk powder were both improved after subcritical extraction.In conclusion,HYP under 1000 U/g and further defatted by subcritical propane extraction has low fat content and desirable functional properties,showing a good application prospect.Finally,the effective components from egg yolk oil obtained from subcritical extraction were further separated.Triglycerides were separated by cold crystallization at low temperature,and then cholesterol and phospholipid were separated by β-cyclodextrin(β-CD)embedding method.The optimal conditions for cholesterol removal were as follows: the molar ratio of β-CD to cholesterol was 5,and the temperature was 50℃.The removal rate of cholesterol was 95.53% and the retention rate of phospholipid was 92.48%.The yield of triglyceride,cholesterol and phospholipid in EYO was 74.80%,94.23% and 96.48%,respectively. |
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