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The denaturation (loss of protein through aggregation and/or change in secondary structure) and physical characteristics such as powder morphology, particle size and size distribution, amorphous/crystalline behavior, and solubility of whey protein isolate (WPI) were investigated in a spray-drying process. The protective efficacy of sugars (lactose and trehalose) and low-molecular-weight surfactant polysorbate-80 (Tween-80) on the secondary structure (b-turn, b-sheet and a-helix) and physical characteristics of spray-dried WPI was quantified. The WPI, WPIþsugar, and WPIþTween-80 formulations were spray dried maintaining the total solids at 10% (w/w). The inlet and outlet temperatures were maintained at 180 and 80 C, respectively. The results showed that the loss of protein through denaturation and aggregation was not significant (p > 0.05). However, a significant (p < 0.05) alteration of the secondary structural elements was observed. Due to spray drying of WPI without protectants, the b-sheet and b-turn were decreased by 4.4 and 14.5%, respectively, and the random coil increased by 20.7%. The a-helix of WPI remained unaltered during the spray-drying process. The presence of Tween-80 effectively protected the a-helix and b-sheet but the b-turn remained vulnerable and was decreased. No significant (p > 0.05) change in the solubility of WPI was observed due to spray drying. Spray drying of WPIþsugar produced essentially amorphous particles. The dried powder particles were spherical with wrinkled or folded surface.

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