High-moisture extrusion of peanut protein-/carrageenan/sodium alginate/wheat starch mixtures: Effect of different exogenous polysaccharides on the process forming a fibrous structure

Abstract: Of particular interest in this present work is to gain knowledge about the process forming the fibrous structure of peanut protein affected by carrageenan (CA), sodium alginate (SA), and wheat starch (WS), respectively. The multi-scale structure and physicochemical properties of exogenous polysaccharide modified-peanut protein powder (PPP) in the six extrusion zones were widely investigated to explain the process forming a fibrous structure. Results showed that 0.1% CA could significantly improve the tensile resistant force (about 1.92 kg), but it was not conducive to the fiber orientation. 0.1% SA could significantly improve the fibrous degree (up to about 1.24), springiness, and the tensile resistant force, but the hardness and chewiness increased significantly. The larger the amount of WS (0–8%), the lower the fibrous degree was, and the hardness and chewiness were both significantly reduced. Furthermore, 0.1% CA, 0.1% SA or 2% WS can protect the molecular chains of conarachin and arachin from the thermal transition. The selected exogenous polysaccharides, especially the 2% WS, can promote the aggregation of protein molecules mainly by breaking the intramolecular disulfide bonds, enhancing the hydrophobic interactions and increasing the apparent viscosity to stabilize the newly formed conformation. The protein subunit with a molecular weight of 22 kDa can be largely impacted by the exogenous polysaccharides due to the degradation of the subunits at 42 kDa and 39 kDa. Additionally, 2% WS can further promote the synthesis of protein subunits with larger molecular weight (66 kDa). The three exogenous polysaccharides can promote the opening of the α-helix and gradually converting into the β-turn and random coil structure. When mixing the PPP with 0.1% CA, the four protein secondary structures were present with β-sheet > α-helix > β-turn > random coil in the extrudate. While mixing the PPP with 0.1% SA or 2% WS, the order was β-sheet > β-turn > α-helix > random coil. This study has provided useful information for producing vegetable protein-based meat substitutes with rich fibrous structure by adding the exogenous polysaccharides.