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Abstract

Spray-drying increases shelf-life and convenience of egg yolk, but may induce damage to its functional properties. The objectives of this study were to investigate the functional properties of spray-dried yolk powders as a function of different pH (3 to 9) and dilution (2- to 10-fold) pre treatments, and to study the impact of spray-drying on functional properties of yolk pellet, the fraction remaining after removal of water-soluble components. Protein solubility and emulsifying properties (Emulsifying Activity Index and Emulsion Stability Index) were considered. Pre-drying pH and dilution had significant effects on protein solubility of the spray-dried powders (p < 0.0001). Protein solubilities of liquid and spray-dried yolk were ~ 70 % and 50 %, respectively. Highest solubility (> 60 %) was obtained when predrying pH was between 5.5 to 9 and dilution between 4- to 9-fold, while emulsions of the yolk powders were most stable when pre-drying pH was between 8.0 to 10.0 and dilution between 2- to 4-fold. Based on the protein functionality test results, the best pretreatment condition would be pH 8.5 with 6 times dilution and the worst condition would be pH 3.0 with 6 times dilution. Pellet powder was relatively insoluble (25 % protein solubility) and its emulsion was less stable. Interestingly, liquid pellet gave better emulsion stabilization than commercial liquid yolk. Freeze-drying produced dried yolk with better emulsion stability than spray-drying. However, duration of storage and batch-to-batch variation of commercial yolk might have influenced the results. Differential Scanning Calorimetry showed similar thermograms for yolk powder with best pretreatment conditions, liquid yolk and spray-dried yolk control (T[sub d] ~ 80°C). Almost no denaturation peak was detected for pellet samples or yolk powder with the worst pretreatment conditions. Results showed that water-soluble fraction of yolk was the main contributor to the thermal behavior of yolk, and freeze-dried yolk samples were more labile to heat denaturation when reconstituted at pH 3 than at higher pHs. The Raman spectra of yolk samples were dominated by vibrational bands of the lipid components, and therefore possible differences in lipoprotein structure as a function of spray drying could not be detected.