| Egg yolk is widely used in food processing industry because of its excellent emulsification,gelation,Water Holding Capacity(WHC)and other processing properties.Egg yolk is often processed into egg yolk powder for convenience.However,due to the high temperature of sterilization process and drying process,the properties of yolk powder will be affected.Therefore,in order to improve the processing performance of yolk powder,glutamine transaminase(TGase)was used to modify the yolk liquid,and obtained the yolk powder by spray drying in this paper.The effects of TGase treatment conditions and spray drying conditions on the processing performance of egg yolk powder were studied in this paper.The main results are as follows:1.Study on the optimal conditions for TGase to influence the processing performance of egg yolk powderTGase can cross-link the proteins in egg yolk powder to improve the emulsification,solubility,gelling hardness and water retention of egg yolk powder.The optimal conditions for the effect of TGase treatment on the emulsification of egg yolk powder were: p H value of 8,enzyme treatment temperature of 40℃,enzyme addition amount of 1.12 U/g of egg yolk,and enzyme treatment time of 3.75 h.Under these conditions,the emulsification of yolk powder reached 2.498±0.016,which was 7.766% higher than that of the blank group.The optimal conditions for the effect of TGase treatment on the solubility of egg yolk powder were: p H value of 8.5,Na Cl concentration of 0.5 mol/L,enzyme dosage of 1.18U/g of egg yolk,enzyme treatment time of 3.5 h,and enzyme treatment temperature of45℃.Under these conditions,the solubility of yolk powder reached 34.561±0.007 mg/g,which was 24.166% higher than that of the blank group.The optimal conditions for the influence of TGase treatment on the gelling hardness of egg yolk powder were: p H value of 7.5,Na Cl concentration of 0.6 mol/L,enzyme addition amount of 2.5 U/g egg yolk,enzyme treatment time of 3 h,enzyme treatment temperature of 35℃.Under these conditions,the gelling hardness of yolk powder reached 73.475±0.599 g,which was48.867% higher than that of the blank group.The optimal conditions for the effect of TGase treatment on the water retention of egg yolk powder gelling were: p H value of 8,Na Cl concentration of 0.7 mol/L,enzyme dosage of 1 U/g egg yolk,enzyme treatment time of 2 h,enzyme treatment temperature of 45℃.In this condition,the gelling water retention of the yolk powder solution was 99.716 ±0.028%,which was 0.351% higher than that of the blank group.2.Study on the optimal conditions for the influence of spray drying conditions on the processing performance of yolk powderThe effect of spray drying conditions on the emulsification and solubility of yolk powder was as follows: with the increase of the feed temperature,the emulsification and solubility first decreased and then increased.At the feeding temperature of 45℃,the emulsifying property reaches the lowest value.When the feeding temperature was 45℃,the solubility reaches the lowest value.When the inlet temperature was 160℃ and the feeding rate was 45%,the emulsification and solubility reached the maximum.The influence of spray drying conditions on the gelling hardness of yolk powder was as follows:the inlet temperature was 155℃,the feeding rate was 45% and the feeding temperature was 45℃.Under these conditions,the gelling hardness of egg yolk powder could reach56.33±0.179 g.The influence of spray drying conditions on the water retention of yolk powder gelling was as follows: inlet temperature 165℃,feeding rate 40% and feeding temperature 45℃.Under these conditions,the water retention of yolk powder gelling could reach 99.602±0.013%.3.Preliminary study on the mechanism of TGase’s effect on the processing performance of egg yolk powderThe results of particle size experiments showed that under certain conditions of enzyme treatment,the cross-linking reaction could lead to the cross-linking of small-molecule proteins to form proteins with larger molecular weight,so as to increase the particle size of the yolk powder emulsion,thus affecting the solubility and emulsification.Through the analysis of the results of infrared spectroscopy experiments,it was concluded that under certain conditions of enzyme treatment,the ban-helical and ban-folded components of the secondary structure of the protein in the yolk powder were transformed into each other under the action of TGase,which changed the oil-water interface tension of the emulsion to affect the size of the solution,and then affected the solubility and emulsification of the yolk powder.By SDS-PAGE electrophoresis experiment results and the number of surface thiol experiment results analysis: under the condition of a certain enzyme treatment,small molecule protein crosslinking form a certain space network structure of macromolecular protein,water molecules into the combination with protein peptide,the peptide chain between thiol cracking,into disulfide bond,affecting the gelling hardness and water retention of the egg yolk powder. |
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