Effects Of Ultrasonic Treatment,Phosphorylation Combined With TGase Cross-linking On The Hardness And Water Holding Capacity Of Egg White Thermal Gel

To improve the thermal gel hardness and water holding capacity of fresh egg white,this study improved the thermal gel hardness and water-holding capacity of desugared egg white through ultrasonic treatment,phosphorylation combined with transglutaminase（TGase）cross-linking composite modification.To reduce the transportation and preservation cost,and broaden its scope of application,it is processed into egg white powder.Ultrasonic treatment,phosphorylation,and TGase enzyme cross-linking are widely used in food processing,but a single modification method has limited improvement in egg white thermal gel hardness and water-holding capacity.In this experiment,the treatment conditions of single modification were optimized through a comprehensive test and orthogonal test,and then the egg white was subjected to compound modification,and the thermal gel hardness and water holding capacity were used as indicators to analyze the modification mechanism.Finally,it was spray-dried into powder,and determined thermal gel hardness and water-holding capacity of egg white powder and observed of its morphology.Below are key research results:（1）Optimum conditions for ultrasound treatment on egg white thermal gel hardness and water holding capacity were optimized by single factor and comprehensive experiments.The results showed that the best ultrasonic conditions were 450 W ultrasonic power and 3 min ultrasonic time.Under these conditions,the thermal gel hardness of egg white was 222.849 g,and the water holding capacity was 41.4%,which were 40.8%and 3.4%higher than the blank.（2）Optimizing the optimal conditions of phosphorylation treatment on egg white thermal hardness and water holding capacity through single factor and orthogonal experiments.The results showed that the optimum conditions for phosphorylation were 0.8%STP,3 h,40℃,and p H 9.Under this condition,the thermal gel hardness of egg white was 203.919 g,and the water holding capacity was 51.5%,which was 57%and 28.2%higher than the blank.（3）The optimal conditions of ultrasonic treatment,phosphorylation combined with TGase cross-linking compound modification on the hardness and water-holding capacity of egg white thermal were studied.The results showed that:the ultrasonic treatment,TGase cross-linking,and phosphorylation treatment group successively obtained the maximum thermal gel hardness of 296 g and water holding capacity of 49.5%,which were respectively increased by 108.8%and 16.5%compared with the blank;phosphorylation treatment achieved a maximum thermal gel hardness of 247.798 g and a water holding capacity of 49.3%,respectively increased by74.8%and 16.1%compared with the blank;single modified phosphorylation treatment achieved a maximum thermal gel hardness of 201.98 g and a water holding capacity of 43.4%.Compared with the blank,it has increased by 42.5%and 1.9%.（4）The mechanism of the effect of composite modification on the hardness and water-holding capacity of egg white thermal gel was discussed.SDS-PAGE showed that the composite modification did not affect the primary structure of egg white protein,but mainly affected the secondary and tertiary structures.FTIR showed that each modification method had obvious absorption peaks at the amide I band,amide II band,and 3200-3500 cm^-1.After ultrasonic treatment and phosphorylation of egg white,smaller particles were generated,and the particles generated by TGase cross-linking were larger.The particle size of the composite modification is determined by the modification order.Theζ-potential,surface hydrophobicity,and exposed sulfhydryl（ESH）of the composite-modified egg white were improved compared with the blank,and total sulfhydryl（TSH）decreased slightly.（5）The effects of spray drying on the hardness and water-holding capacity of composite-modified egg white thermal gel were studied.The results showed that the maximum hardness of the thermal gel was 126.141 g and the water holding capacity was 50.8%,which was 24.5%and 12.8%higher than that of the blank.After TGase cross-linking and ultrasonic treatment,the maximum thermal gel hardness was 114.848 g,and the water holding capacity was 45.6%,which was 13.4%and 1.3%higher than that of the blank.The maximum hardness of the hot gel obtained by a single modified ultrasonic treatment was 109.475 g,and the water holding capacity was 47.4%,which was 8.1%and 5.4%higher than that of the blank.SEM showed that the surface of the particles in the blank group was rough,and there was a certain degree of aggregation among the particles.The surface of the particles in the modified treatment group was smoother and the pores were larger.The aggregation of ultrasonic treatment and TGase crosslinked particles was more obvious,and the particles in the phosphorylation treatment group were more dispersed.