Impact of pH, temperature, and moisture on the rheological behaviour of soy protein concentrate doughs

The texture of plant-based meat analogues manufactured by high-moisture extrusion is governed by the rheological properties of the extruded protein dough. However, there is currently little understanding of how dough formulation and extrusion temperatures impact these properties. Hence, we used closed-cavity rheometry (CCR) to characterise soy protein concentrate (SPC) doughs under conditions varying in protein source, pH, moisture content M, and temperature T. We then fitted both a constitutive Herschel-Bulkley (HB) model to steady-shear data and a descriptive model to strain sweep data. Subsequently, a Multiple Linear Regression (MLR) model was applied to link the experimental factors and model parameters. We show that the temperature and moisture effects can be aggregated via the ratio Tg/T, with Tg being the moisture-dependent glass transition temperature. The yield stress τ0, elastic modulus G0, and the loss factor tan (δ) were influenced primarily by Tg/T and, to a lesser degree, by the pH of the dough. In contrast, parameters describing rheology at high shear rates, the critical shear rate and the strain thinning index, are not affected by formulation, pH, moisture, or temperature. The protein solubilities of the two SPCs were significantly different, yet we observed similar rheological behaviour when their doughs were shifted to the same pH. Taken together, our work identifies important parameters towards optimising processing conditions for plant-based meat analogues.