Concentration of native whey through Refractance Window Drying (RWD) for the production of a novel ingredient containing galacto-oligosaccharides and functional proteins

This study evaluated Refractance Window Drying (RWD) as a novel method to concentrate native whey for the production of a bifunctional ingredient rich in galactooligosaccharides (GOS) and functional whey proteins. Native whey was concentrated under various RWD conditions (40–80 °C; 2 and 3.4 mm thicknesses) and compared to vacuum concentration in terms of color, α-amino group content, foaming properties, drying kinetics, and GOS synthesis capacity.Drying kinetics were modeled using Fick's second law and anomalous diffusion models. RWD significantly reduced drying time, with effective diffusivity ranging from 4.01 × 10 −10 to 1.65 × 10 −8 m 2 /s. A transition from super-diffusive to Fickian behavior was observed between 60 °C and 70 °C, likely due to protein denaturation. Color and foaming were best preserved at 40–60 °C, indicating minimal protein glycation. At 70 °C, optimal performance was observed, balancing shorter drying time, α-amino group retention, and functional stability. GOS synthesis using Aspergillus oryzae β-galactosidase was enhanced in RWD-concentrated whey, achieving higher yields (up to 27%) and faster lactose conversion than in commercial formulations. The absence of additives in RW whey improved lactose availability for enzymatic conversion. These findings position RWD as an efficient and gentle technology for producing multifunctional dairy ingredients suitable for functional foods, infant nutrition, and nutraceuticals.