The effect of transglutaminase, oleogel/hydrogel ratio, and NaCl addition on the structural and textural properties of pea protein/candelilla wax-based bigels

Recent trends promote the replacement of animal-based products using plant sources. Such food alternatives can be achieved utilizing bigels, tailorable materials which combine plant protein-based hydrogel (HG) and oleogel (OG) phases into one gel system. The effect of salt addition, commonly used in the food industry, into plant-based bigel formulation based on pea protein hydrogel and candelilla wax oleogel is the main goal of this research while the effect of transglutaminase (TG) cross-linker concentration (0-20 % out of the protein mass) and OG/HG ratio (30/70-60/40) were also examined. Overall, bigel composition of 10 % TG, which was found vital for consistency, and 40/60 OG/HG ratio, which was found preferable with respect to mechanical strength and appearance, was used to thoroughly explore the effect of salt addition. The results show that NaCl significantly impacts the bigel structure and performance. More specifically, increase salt concentration transitioned the bigel structure from OG-in-HG type to an unorganized bi-continuous-like microstructure. These structural changes were correlated to protein screening effect of the salt ions which affected the bulk gelation and interfacial properties of the protein. The mechanical behavior demonstrated a transition from flaky and brittle texture to softer and spreadable texture with elevated salt concentrations. Moreover, all bigels thermal rheology showed an abrupt softening due to oleogel melting finalized by increasing moduli around protein denaturation point. It seems that TG concentration and OG/HG ratio have a significant impact on the bigel properties, while even a low concentration of NaCl can significantly alter the bigel performance and thus should be considered while developing a specific alternative product.