Controlled ball milling enhances the lubrication performance of proso millet flour dispersions

Proso millet flour (PMF) is a sustainable cereal ingredient with significant potential for nutritional and functional food applications. This study investigated the effect of high-energy ball milling (BM) at two specific energy inputs, 31 J g−1 (BM-31) and 62 J g−1 (BM-62), as a solvent-free strategy to enhance the tribological properties of PMF suspensions (15% w/v). Fourier-transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), rheology, tribology, and microscopy across multiple length scales were used to understand the relationship between structural modification, hydration, and frictional behavior. Among the treatments, BM-31 produced the most significant reduction in particle size and disruption of the ordered structure, resulting in approximately ten-fold and three-fold increases in cold-water solubility and swelling power, respectively, compared with its native counterparts. The improved hydration increased the bulk apparent viscosity and promoted the formation of a soft, hydrated, and viscous adsorbed film, thereby reducing friction through the development of a load-bearing lubricating layer. As a result, the BM-31 sample produced an order-of-magnitude reduction in friction coefficient (μ = 0.03) and a higher estimated minimum film thickness (hmin = 0.69 μm) compared with native PMF (μ = 0.56; hmin = 0.05 μm) at an entrainment speed of 0.005 m s−1. The BM-31 sample showed strong concentration-dependent lubrication behavior, indicating that tribological performance was influenced not only by sample hydration behavior but also by particle concentration. Overall, controlled ball milling can be used as an effective strategy for improving lubricity of cereal flours by modulating particle size, structural order, and hydration capacity.