High-moisture soy protein extrudates with different moisture contents: Texture, structure, and in vitro digestion characteristics.

High-moisture extrusion (HME) is a promising physical modification method that is extensively used to create fibrous meat analogs from plant-based proteins, attracting considerable research interest. Although a substantial amount of existing research has focused on HME with moisture contents between 60 % and 65 %, investigations of HME with moisture contents ranging from 70 % to 75 % are limited. This study examined the effects of extrusion modification with varying moisture contents (55-75 %) on the textural, structural, and digestive properties of soy protein isolate (SPI). Textural and rheological analyses revealed that extruded SPI progressively softened as the moisture content increased. The highest anisotropy index was detected at 65 % moisture content, which corresponded to the highest β-sheet content in the secondary structure analysis. Low-field nuclear magnetic resonance revealed a shift from bound water to fixed water in the extrudates as the moisture content increased. Dynamic in vitro digestion experiments revealed that extrudates with high moisture contents were more susceptible to digestive fluids, leading to smaller particle sizes after digestion and increased digestibility. Moreover, extrusion processing decreased the β-sheet content, leading to the destabilization of the protein molecules. This destabilization notably decreased SPI solubility; however, it simultaneously increased protein digestibility. The present study elucidates the association between moisture content and the extrusion properties of SPI, providing valuable insights for developing innovative plant-based products.