Plant-based Proteins and Gums Dictate Rheology of Plant Milks

The rapid increase in demand and production of plant milks, i.e., the plant-based alternatives to animal milks, is driven by lactose intolerance, allergens, and religious, cultural, environmental, and health choices or concerns. Many challenges for emulating animal milk's physicochemical, functional, and sensory attributes can be translated as problems related to their flow behavior. In this study, we characterize rheology of commercial animal and plant-based milk formulations, detailing challenges posed by interfacial adsorption of proteins, influence of dissolved gums or polysaccharides on interfacial and suspensing fluid properties and characterization of extensional rheology of such low viscosity fluids. Only a few studies characterize shear rheology and almost none show characterization of extensional rheology of animal milks (cow and goat) and plant milks (soy, almond, rice, coconut, pea, and oat). We find that the two animal milks have rate-independent shear viscosity responses similar to Newtonian fluids. In contrast, the plant milks, except rice milk, display shear thinning. Using dripping-onto-substrate (DoS) protocols, we show that in the last stage of pinching, plant milks show inertiocapillary, power law, or elastocapillary pinching, whereas animal milk displayed a viscocapillary response. The distinct rheology response of animal and plant milks can be correlated to the role of dispersed colloidal particles, drops, and macromolecules, and distinct interfacial adorption and rheology of animal vs plant-based proteins.