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K. S. TANG, Food, Nutrition & Health, Faculty of Agricultural Sciences, The University of British Columbia, Food Science Bldg, 6650 NW Marine Drive, Vancouver, BC V6T 1Z4, Canada

Egg yolk can be made into a product of longer shelf-life and convenience after spray drying. However, the drying conditions, including pre-drying pH and solids content of the liquid yolk, may change the functional properties of the final product. In recent years, there has been interest in yolk immunoglobulin (IgY) as a source of antibodies in functional foods and pharmaceuticals. The yolk pellet remaining after extraction of IgY may be useful as a food ingredient.

The objectives are to investigate functional properties of yolk powder spray-dried after different pH and dilution pretreatments, or after removal of the water-soluble fraction containing IgY.

Effects of pre-drying pH (3 to 9) and dilution (2- to 10-fold) were investigated using response surface methodology. Yolk pellet was prepared as the insoluble fraction after 10-fold dilution with water at pH 5.2. Protein solubility, emulsifying activity and stability were measured after reconstitution of yolk powders at pH 6.3. Proximate analysis of yolk, pellet and powders was determined.

Control spray-dried yolk powder had lower solubility (~50%) than commercial liquid yolk (~70%). Pre-drying pH and dilution significantly affected protein solubility of yolk powder (p<0.0001). Highest solubility (~60%) was obtained with pre-drying pH of 6.4-8.3 and dilution of 5.3- to 8-fold. Emulsions prepared with yolk powder were most stable with pre-drying pH between 8.0 and 10.0, and dilution between 2- to 4-fold. Yolk pellet powder was relatively insoluble and yielded less stable emulsions, while liquid yolk pellet gave better emulsion stabilization than commercial liquid yolk despite its low solubility.

These results aid in identifying optimal conditions of pre-drying pH and dilution for spray drying of yolk, and provide support for using yolk pellet in food processing.