Tannic acid addition modulates the gelling properties of soybean and faba bean proteins differently

The gelling properties of plant proteins are often considered inferior to those of animal-based proteins, which is why there is an increasing interest in strategies to modulate that functionality. Ideally, such strategies are general and applicable to various plant proteins, rather than only specific ones. Here, we test the effect of tannic acid (TA) on the gelling properties of commercial soy and faba protein isolate (SPI–C and FPI–C) to extrapolate common behaviour. Chemical characterisation revealed that SPI–C was denatured and aggregated, whereas FPI–C contained native proteins with a smaller particle size (SPI–C: d4,3 = 34.3 μm ± 6.1, FPI–C: d4,3 = 10.4 μm ± 4.6). Alkaline treatment (pH 9, 24 h) was applied to favour covalent modification of both isolates with TA. The ratio of covalent to noncovalently bound TA was higher for FPI–TA than for SPI–TA, likely because of the higher availability of TA binding sites on the native FPI–C. Higher covalent cross-linking within FPI–TA resulted in significant functional changes: a 10-fold increase in dispersion viscosity, a 20% increase in gel deformability, and a 3-fold increase in fracture stress. However, only slight differences were observed in the functional properties of SPI–TA. TA addition can be a powerful tool to enhance the gelling properties of plant proteins, albeit the potential of the modification depends on the interaction capacity with the phenolic compound and the physicochemical properties of the proteins at the start.