Rheology of Pickering vs. non-Pickering high internal phase emulsions stabilized by morphology-tunable tannic acid-chitosan complex

The role of emulsifier morphology in shaping the rheology of food-grade Pickering and non-Pickering high internal phase emulsions (HIPPEs and HIPnPEs) remains difficult to isolate, as previous comparisons often involved simultaneous variations in emulsifier identity and morphology. Here, we exploit the pH-induced coil-to-aggregate transition of tannic acid–chitosan complexes (TACS) to prepare component-consistent molecular and particulate emulsifiers, enabling a morphology-focused comparison. Small-amplitude oscillatory shear (SAOS) tests show that TACS particle packing provides HIPPEs with an additional elastic contribution, resulting in higher storage moduli than their HIPnPE counterparts and marked positive deviations from the Princen–Kiss prediction. Under large-amplitude oscillatory shear (LAOS), TACS-stabilized HIPPEs exhibit Type I network breakdown, whereas the HIPnPE counterparts display Type III behavior with more pronounced strain hardening and shear thickening. These contrasting responses suggest that TACS-stabilized HIPPEs may be suited to firm, rest-stable foods, whereas the HIPnPE counterparts may benefit processing that requires structural recovery. By isolating emulsifier morphology as the primary variable, this work identifies its contribution to rheology of high internal phase emulsions and provides a model strategy for morphology-directed rheological design.