Effect of spray drying and fluidized bed drying on whey protein phospholipid concentrate: Microstructural analysis, bioactivity, and functionality

Whey protein phospholipid concentrate (WPPC) is a valuable coproduct of whey protein isolate that represents a rich source of bioactive compounds with potential health-promoting benefits. Powdered forms of dairy ingredients are highly valued for their convenience and extended shelf life. However, drying is a crucial process that can affect microstructure, bioactivity, and physicochemical properties. This study investigated the effect of 2 drying methods, spray drying and fluidized bed drying, on the properties of WPPC (SD-WPPC and FBD-WPPC, respectively) with an industry-scale spray-dried WPPC (I-SD WPPC) also included as a control to represent scaled-up production. After rehydration, FBD-WPPC exhibited a particle size (2.22 µm) comparable to SD-WPPC (1.72 µm) and I-SD WPPC (2.72 µm), and the mean milk fat globule diameters did not differ substantially among FBD-WPPC (10.93 µm), SD-WPPC (11.51 µm), and I-SD WPPC (11.29 µm). Furthermore, confocal laser scanning microscopy revealed larger aggregates of protein and fat in the SD-WPPC and I-SD WPPC, whereas FBD-WPPC showed a more uniform protein distribution with distinct fat clusters. Fourier-transform infrared analysis indicated that FBD-WPPC retained the most native-like protein secondary structure, SD-WPPC displayed moderate structural changes, and I-SD WPPC exhibited the most pronounced alterations, with decreased α-helix and random coil contents and increased β-sheet and β-turn contributions. Xanthine oxidase activity normalized to protein content was significantly higher in FBD-WPPC than in both spray-dried powders, which did not differ from one another, demonstrating the influence of drying method on milk fat globule membrane-enzyme stability. Protein oxidation, as measured by carbonyl content, was determined to be the lowest in I-SD WPPC but significantly not different among samples. Both primary (lipid hydroperoxides) and secondary (thiobarbituric acid reactive substances) lipid oxidation products showed no significant differences among FBD-WPPC, SD-WPPC, and I-SD WPPC. Overall, these results provide new insight into how different drying methods and processing scales influence the microstructure and physicochemical properties of WPPC, informing future development of functional dairy coproduct powders.