Effect of different enzyme pretreatment on the formation and gel properties of soy protein nanofibrils

Preparing nanofibrils through protein self-assembly reactions can modulate the structural and functional properties of plant proteins , resulting in gels at lower protein concentrations. This experiment investigated the effects of pretreatment under various enzymatic conditions on the formation process and gel properties of soy protein nanofibrils (SPF) under acid-heat conditions (pH 2.0, 85 °C, 0–24 h). Bromelain (Bro), trypsin (Try), and papain (Pap), which target different hydrolysis sites, were selected for the treatment of soybean protein isolate (SPI). Results indicated that SPF developed into a self-supporting hydrogel after heating 18 h, whereas SPF-Bro, SPF-Try, and SPF-Pap formed after 10, 8, and 12 h of heating, respectively. Enzymatic digestion of proteins can accelerate the progress of fibril formation while enhancing the conversion rate of the fibrils. Trypsin demonstrated the most significant modification effect, achieving the highest fibril conversion rate of 62.70 ± 1.65%. The gel strength and viscosity of all enzyme-modified nanofibrils were higher than that of SPF, in which the intertwining of a large number of fibrils of SPF-Try increased the gel strength by more than one order of magnitude compared with that of SPF. Consequently, moderate enzymatic modification can enhance fibril formation and improve the gel properties of SPF. These experimental findings will contribute to advancing the development of SPF in food and biomaterials.