Research On Preparation And Application Of Dried Egg Yolk With Phospholipase

Egg yolk is widely used as a natural emulsifying agent in numerous processed food such as ice-cream, mayonnaise, margarine and baking food owing to its effective emulsifying property. However, it is heat-sensitive and begins to coagulate at high temperature, which results in drastically decreasing in emulsifying property. Phospholipase A2 (PLA2) can hydrolyze lecithin of yolk into lysolecithin,providing modified egg yolk better functional properties, especially heat stability. As a result, modified egg yolk is more widely used in processing food.First, technologcial conditions of egg yolk lecithin hydrolysis with PLA2 and spray drying parameters were studied systematically. Based on the released FFA, the effect of factors on the degree of conversion was studied, and the optimal parameters were determined as follows: the initial pH value was 7.5, processed temperature was 45℃, E/S was 2000U/g yolk, reaction time was 2 hours, independent of Ca2+, and the degree of hydrolysis was 81.83%.And the conditions of spray drying were investigated. The optimal inlet air temperature of spray drying was 180~200℃.Then the functional properties of dried modified egg yolk (DEY-M) were also investigated. DEY-M proved better on moisture adsorption capacity and fat absorption capacity, it is important that Emulsifying capacity (EC) of DEY-M has been improved 25%, and by the study of emulsion stability of DEY-M, The DEY-M has better emulsion stability than DEY-C in the condition of high temperature, high pH and high quantity of salt In addition, the effects of PLA2 on the characteristics of bread, noodle and icecream were studied. The bread which added DEY-M has been obviously improved on the texture properties and specific volume, and DEY-M improved on the quality traits and texture properties of noodles. By studied on icecream, DEY-M proved better on overrun and the melting of icecream.Finally, the effects of DEY-C and DEY-M on the rheological properties of wheat flour dough were investigated using scanning electron microscopy (SEM), rheometer, Brabender farinoghaph and extensoghaph. The measured dough properties were dough development time, stability, extensibility, resistance, elastic modulus and viscous modulus. Dried modified egg yolk increased the dough properties and improved the wheat dough rheological properties.