High-moisture extrusion enhances soy protein quality based on in vitro protein digestibility and amino acid scores

Plant-based meat analogues, often used as an alternative to meat-based products, have grown in popularity. The processing conditions used to create these analogues determine the structural properties of the proteins, but their impact on protein quality is underexplored. Therefore, this study describes the impact of a broad range of high-moisture extrusion (HME) process conditions (100-160 °C and 50-70 % moisture content) on the amino acid score and in vitro protein digestibility of extrudates made with soy protein concentrate (SPC) and soy protein isolate (SPI) in addition to the physical properties (water-holding capacity, hardness and particle size). It was found that the physical properties of both SPC and SPI extrudates depended more on moisture than on the set process temperature profile. HME (at >60 % moisture) enhanced the overall in vitro protein digestibility for SPI- and SPC-based extrudates relative to the starting material, despite the significant negative correlation (p < 0.05) with decreasing moisture content and, thus, sample hardness. Furthermore, compared with the starting materials, amino acid scores hardly decreased (maximum 7 %) and remained >100 across a wide range of processing conditions, except for SPI-based extrudates extruded at 120 °C and 50 % moisture content. In conclusion, most of the HME conditions currently used for making meat analogues significantly affect their physical properties and enhance in vitro protein digestibility, but have minimal impact on the amino acid score.