Abstract: This study aimed to achieve the efficient application of whey protein powder (WPP) in pasteurized fermented milk. To this end, 18 WPP samples from six countries were collected and measured for solubility, hydrated particle size, particle size after acid-heat treatment, and gel strength. Based on these parameters, WPP was categorized into four types: gelled, isolated, micronized, and heat stable. Subsequently, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) was applied to determine the protein composition, and field-emission scanning electron microscopy (FE-SEM) was utilized to characterize the particle morphology. Finally, the texture and sensory attributes of fermented milk supplemented with these WPP samples were evaluated. The results indicated that the content of active whey protein was the critical factor for the functional classification of WPP. The active whey protein contents in these types of WPP ranked in a descending order: isolated > gelled > heat stable > micronized. Additionally, higher active whey protein contents resulted in greater viscosity of fermented milk but also intensified the powdery astringency and pasty mouthfeel, ultimately reducing consumer acceptance. The functional classification method proposed in this study offers guidance for the targeted application of WPP and provides a theoretical foundation for developing fermented milk products with diverse texture characteristics.

Key words: whey protein powder; functional properties; classification method; fermented milk; textural properties; active protein content