Cold–set gelation of soybean and amaranth proteins: heat versus high hydrostatic pressure in the presence of calcium

Abstract The feasibility of developing a powder that gels upon rehydration, suitable for safe swallowing in dysphagia, was assessed. These gels were prepared from mixtures of soybean and amaranth proteins (4%w/w protein), denatured in the presence of calcium by high hydrostatic pressure treatment (HHP, 600 MPa – 5 min – 20 °C) or heat (95 °C–25 min); the samples were subsequently freeze-dried and rehydrated to 13%w/w protein. By applying multiple response surface methodology (MRS), different percentages of amaranth protein (10–30%) and different Ca:protein ratios (0.075–0.250 mmol Ca/g protein) were evaluated. Moreover, tests were performed using individual soybean and amaranth proteins to elucidate the phenomena observed in the mixtures. In mixtures, with both denaturing treatments, soybean proteins established the three-dimensional matrix. Amaranth proteins, in contrast, acted as a filler that weakened the matrix and worsened the water holding capacity, likely due to their low solubility. Increasing the calcium content had significant effects on most characteristics of the heated samples, but not on the pressurized ones. For both treatments, the optimal condition for preparing the gels was with the lowest proportion of amaranth proteins tested (10%), and the optimal calcium content for HHP was higher than for heating (0.25 and 0.17 mmol Ca/g protein, respectively). These gels exhibited apparent viscosity values (at 50 s − 1 ) between 0.8 and 1.5 Pa•s, which can be considered therapeutic for dysphagia. When tested individually, only soybean proteins were able to gel using this strategy, whereas amaranth proteins were not.