Rheological behavior and color stability insights into yerba mate ( Ilex paraguariensis ) ultrafine suspensions with nanocellulose as a structuring agent

Yerba mate (YM) (Ilex paraguariensis A. St-Hil.) is a South American plant traditionally consumed as an infusion, but its chemical complexity and bioactive composition support broader applications as a natural food ingredient. This study evaluated the color stability and rheological behavior of colloidal suspensions prepared from ultrafine YM particles and nanocellulose (NC) blends. Color stability was assessed under three pH conditions (4, 7, and 10) during refrigerated storage for 21 days, using CIE Lab* parameters. Acidic and neutral conditions resulted in greater color stability, with marked deterioration at alkaline pH, suggesting promising applications in acidic food systems such as yogurts. Rheological properties were investigated through steady-shear flow curves, oscillatory measurements, and temperature sweeps. All formulations exhibited pseudoplastic shear-thinning behavior, with viscosity increasing in proportion to NC concentration. Model fitting (Ostwald-de Waele and Herschel–Bulkley) confirmed that NC enhanced network firmness, lowered flow behavior index values (n < 0.4), and increased yield stress in mixed systems. Oscillatory analyses revealed predominantly elastic behavior (G’ > G’’), with greater thermal resilience and partial recovery in NC-rich blends. Overall, YM-NC dispersions present potential as multifunctional ingredients, combining natural green coloration with tunable rheological properties for high-value food, cosmetic, and pharmaceutical formulations.