Reinforcement of heat-set whey protein gels using whey protein nanofibers: Impact of nanofiber morphology and pH values

Traditional whey protein isolate (WPI) gels require relatively high protein concentrations and prolonged heating to prepare. They exhibit a limited range of physicochemical attributes. To overcome these disadvantages, in this study, we examined the impact of incorporating whey protein isolate nanofibers (WPIFs) on the properties of heat-set WPI gels. Initially, WPIFs with different morphologies were prepared by varying the time they were exposed to acid heating (pH 2.0, 95 °C). Then, the effects of these WPIFs on the texture, rheology, microstructure, and fluid holding properties of WPI-WPIF composite gels were studied under acidic (pH 2.0) and neutral (pH 7.0) conditions. At both pH values, the gel strength and water holding capacity of the composite gels was significantly higher (P < 0.05) than for simple WPI gels. Moreover, the gelation time was shortened from around 30 min to 14.3 and 8.3 min at pH 2.0 and 7.0, respectively. WPI-WPIF composite gels prepared at pH 7.0 had the highest hardness (3120 Pa), storage modulus (10 kPa), and water holding capacity (94%). Cryo-SEM indicated that these gels had highly porous honeycomb structures with a pore size around 1–2 μm. Hydrophobic, hydrogen, and disulfide bonds played a crucial role in the formation of the composite gels at pH 7.0, but only hydrophobic and hydrogen bonds played a crucial role at pH 2.0. The impact of the WPIFs on the properties of the composite gels depended on their morphologies. The novel composite gels created in this study may have applications in the food and other industries.