Description:
The denaturation kinetics of whey protein isolate (WPI), in the presence and absence of lactose and trehalose, was quantified in a convective air-drying environment. Single droplets of WPI, WPI-lactose and WPI-trehalose were dried in conditioned air (2.5% RH, 0.5 m/s air velocity) at two temperatures (65°C and 80°C) for 500 s. The initial solid concentration of these solutions was 10% (w/v) in all the samples. Approximately 68% of WPI was denatured when it was dried in the absence of sugars. Addition of 20% trehalose prevented the irreversible denaturation of WPI at both temperatures. Thirty percent lactose was required to prevent denaturation of WPI at 65°C and the same amount of lactose protected only 70% of WPI from denaturation at 80°C. The secondary structures of WPI were found to be altered by the drying-induced stresses, even in the presence of 20% trehalose and 30% lactose.
Description:
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 (-turn, -sheet and -helix) and physical characteristics of spray-dried WPI was quantified. The WPI, WPI+sugar, and WPI+Tween-80 formulations were spray dried maintaining the total solids at 10% (w/w). The inlet and outlet temperatures were maintained at 180 and 80 degrees 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 -sheet and -turn were decreased by 4.4 and 14.5%, respectively, and the random coil increased by 20.7%. The -helix of WPI remained unaltered during the spray-drying process. The presence of Tween-80 effectively protected the -helix and -sheet but the -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 WPI+sugar produced essentially amorphous particles. The dried powder particles were spherical with wrinkled or folded surface.