Freezing as a structuring process for protein gels: process–structure relationship, material characterization, and comparison with meats

Abstract

The growing demand for alternative proteins arises from population growth and the pursuit of innovative, sustainable products. Protein gels stand out among these alternatives due to their ability to replicate meat-like sensory properties using proteins such as Soy Protein Isolate (SPI). This study evaluated the production of structured SPI gels via freeze structuring. The variables solids content (X₁), pH (X₂), and freezing temperature (X₃) were analysed in relation to the responses hardness (Y₁) and cohesiveness (Y₂), using a two-level, three-factor full factorial design with a duplicate at the centre point. The results revealed a significant effect of all main effects and they include the interactions solids content × pH and solids content × freezing temperature for Y₁, while for Y₂, the influential effects were solids content, pH, and the interactions solids content × pH and pH × freezing temperature. The Texture Profile Analysis (TPA) and colour of the gels were comparable to those of sirloin steak, chicken breast, and fish fillet. Gels exhibited acidity between 0.079 and 0.167 g of lactic acid/100 g, pH from 5.54 to 6.54, a water activity (a_w) of 0.992 to 0.996, and a moisture content of 63.35% to 69.84%. Treatments S6 (13% solids, pH 5.0, −5 °C), S8 (13% solids, pH 6.0, −5 °C), and S9 (9% solids, pH 5.5, −10 °C) exhibited lamellar structures and a Degree of Texturization (DT) above 1, suggesting unidirectional freezing, confirmed by freezing curves. Overall, freeze structuring proved to be a promising technique for producing structured SPI gels, with optimal parameters being 9% solids, pH 5.5, and −10 °C.