At present, the changes in fibrous structure of plant proteins improved by polysaccharides during high-moisture extrusion cooking (HMEC) are still unclear. In this study, different additions (1, 2, 3, 4, and 5%) of sodium alginate (SA), xanthan gum (XG), and maltodextrin (MD) were used in the preparation of organised protein products based on soybean protein and wheat protein under high moisture extrusion conditions. It was revealed that SA-4%, XG-2%, and MD-2% (w/w) significantly enhanced the structural and physical properties of the fibres. The polysaccharides increased the water distribution of extrudates by enhancing protein-water interactions through hydrogen bonding, with MD-2% having the strongest ability to trap free water. The mechanism by which the polysaccharides improved the fibrous structure of extrudates involved the reorganization of molten proteins from the die head region to the cooling region, formation of new molecular bonds and enhancement of thermal stability. XG-2% significantly increased the β-sheet structure in the molten region (48.9 ± 1.35%) and showed the best thermal stability. Overall, SA-4% was able to better maintain the molecular bonding transformation and strong water absorption, which stabilised the protein conformation and formed the highest fibrous degree (2.1 ± 0.03). This suggests that the properties of the three polysaccharides can be used as modifiers of high water extruded plant proteins to improve the extruded materiality, functional and nutritional properties.

Heat-induced composite gel systems consisting of different soybean protein isolate (SPI) and potato protein (PP) mixtures were studied to elucidate their “backbone” and property changes. This was achieved by comparing the ratio of non-network proteins, protein subunit composition, and aggregation of different gel samples. It was revealed that SPI was the “gel network backbone” and PP played the role of “filler” in the SPI-PP composite gel system. Compared with the composite gels at the same ratio, springiness and WHC decrease with PP addition. For hardness, PP addition showed a less linear trend. At the SPI-PP = 2/1 composite gel, hardness was more than doubled, while springiness and WHC did not decrease too much and increased the inter-protein binding. The hydrophobic interactions and electrostatic interactions and hydrogen bonding of the SPI gel system were enhanced. The scanning electron microscopy results showed that the SPI-based gel system was able to form a more compact and compatible gel network. This study demonstrates the use of PP as a potential filler that can effectively improve the gelling properties of SPI, thus providing a theoretical basis for the study of functional plant protein foods.

BACKGROUND Due to the extrusion black box effect, polysaccharides determine the formation of meat‐like fibrous structures by modulating the flow behaviour and structural changes of plant proteins under high‐moisture extrusion conditions. However, there is limited knowledge on the mechanism of resolution. This study simulated the rheological properties of soy protein–wheat protein under 57% moisture conditions with addition of 4% sodium alginate (SA), 2% xanthan gum (XG), and 2% maltodextrin (MD). The effect of these polysaccharides on the aggregation behaviour and conformation of raw protein during high‐moisture extrusion was investigated. RESULTS It was revealed that the three polysaccharides were effective in increasing the interaction between proteins and between proteins and water. Among them, 4% SA elicited a significantly stronger storage modulus (gelation behaviour) compared to the control. Analysis of different zones of extrudates by protein electrophoresis, particle size, and turbidity showed that SA‐4% was able to form more high molecular protein aggregates (> 245 kDa) and promoted crosslinking of low molecular subunits (< 48 kDa), resulting in moderately sized protein aggregated particles. Fluorescence and ultraviolet spectra showed the transformation of protein tertiary structures in different extrusion zones, confirming that the key extrusion zone for protein conformational transformation by polysaccharides is the die–cooling zone. Furthermore, stretching of polypeptide chains and accelerated protein rearrangement facilitated the formation of more fibrillar structures. CONCLUSION Theoretical support for polysaccharide modulation of plant protein quality in high moisture extruded products is provided by this study. © 2023 Society of Chemical Industry.

In this study, we investigated the effects of high-pressure homogenisation (HPH) combined with Lactobacillus (LAC) induction (43 °C and 8 h) on the gel properties and structure of soymilk protein under different pressures (0,100,110,120,130 and 140 MPa). HPH significantly improved the fermentation rate and gel characteristics of the soymilk. The soybean protein treated at 120 MPa had the best gel characteristics, with shorter gel formation time, higher water-holding capacity and stronger hardness and viscosity. Particle size and protein structure analyses confirmed that the particle size of soy protein was smaller and the protein was more folded at a homogenising pressure of 120 MPa. HPH accelerated the unfolding of protein structure and exposure of hydrophobic groups, facilitating the interaction between LAC and proteins, thereby accelerating the formation of macromolecular aggregates in gels and improving the gelation properties of soy protein. This work established the application prospect of HPH in dairy processing and soybean-based fermentation product development.

Background High‐pressure homogenization (HPH) is commonly used as a non‐thermal processing technique for soybean and soy protein products, and the preparation of soy protein gel products often requires the synergistic effect of HPH and heat treatment. The dissociative association behavior of 11 S is the key to the protein gel formation state. In this study, therefore, 11 S thermal gels were prepared by high‐pressure homogenization and co‐induction (90 °C, 30 min) (adding Ca2+ to promote gel formation before heat treatment), and the effects of different high‐pressure homogenization pressures (0–100 MPa) and co‐treatment on the dissociative association behavior of 11 S protein, gel properties, and microstructure of 11 S gels were investigated. Results The results showed that HPH at higher pressures led to the breaking of disulfide bonds of aggregates and disrupted non‐covalent interactions in protein aggregates, leading to collisions between protein aggregates and the reduction of large protein aggregates. High‐pressure homogenization treatment at 60 MPa improved the gel properties of 11 S more. The HPH combined with heating changed the binary and tertiary structure of 11 S soy globulin and enhanced the hydrophobic interaction between 11 S molecules, thus improving the gel properties of 11 S. The change in intermolecular forces reflected the positive effect of HPH treatment on the formation of denser and more homogeneous protein gels. Conclusion In conclusion, high‐pressure homogenization combined with heating can improve the properties of 11 S gels by changing the structure of 11 S protein, providing data and theoretical support for soy protein processing and its further applications. © 2022 Society of Chemical Industry.