Molecular composition and particle-scale interactions in oat and bovine milks: Development of SEC-based protocols for plant-based milk analysis

Long‑life oat milk is consumed as dairy alternatives for reasons ranging from lactose intolerance to dietary preferences, remain poorly understood in terms of their molecular interactions. This study compared their composition and molecular organization using gravity‑driven size‑exclusion chromatography (SEC), using dynamic light scattering (DLS) for particle size and electrophoretic light scattering (ELS) for surface charge. Content analysis revealed that oat milk contained significantly lower protein (6.2 ± 0.14 mg/mL) than bovine milk (25.2 ± 0.79 mg/mL), higher carbohydrates (62 ± 9.1 mg/mL), and lower fat (24.6 ± 0.66 mg/mL vs. 30.8 ± 5.88 mg/mL). Despite using SEC columns intended for extracellular vesicles, the technique differentiated particles based on more than size alone. Both milks exhibited two main populations—fat–protein and carbohydrate–protein complexes. However, bovine milk fractions showed more uniform component distribution, unlike oat milk where sugar‑rich particles eluted later due differing interactions with the SEC matrix. These findings underscore fundamental structural differences between plant‑based and bovine milk systems. Gaining better insight into these molecular assemblies can enhance analytical methods used in formulation, stability tests, and quality control for plant‑based dairy alternatives.