Physical and chemical properties of soy protein isolates treated with sodium sulphite under low temperature extrusion

Abstract

Summary Soy protein isolates (SPIs) treated with sodium sulphite (Na2SO3) under low temperature (50 °C) extrusion were investigated to create a system where the disulphide bonds were destroyed. The physicochemical properties of the extrudates were characterised after the addition of 0.0%, 1.5% and 3.0% (w/w) Na2SO3. Under these conditions, free sulfhydryl content significantly increased (from 98.46 to 449.64 μmol g−1), specific mechanical energy during extrusion significantly increased (from 426.91 to 593.39 kJ kg−1), degradation temperature reduced (from 315.7 to 302.0 °C), protein solubility of the water extraction increased incrementally (from 5.41% to 20.17%) and water absorption capacity decreased (from 3.51% to 2.69%). Moreover, the addition of Na2SO3 caused a blue shift in the tryptophan fluorescence spectra of soluble SPI. These results suggest that Na2SO3 breaks disulphide bonds in SPI, which accelerates protein molecule denaturation to promote peptide disentanglement; consequently, SPI become more hydrophobic and less thermally stable.

Effects of Extrusion‐Assisted Wet‐milling Isolation on Physicochemical Properties of Corn Starch

“…This could be attributed to strong friction and shearing force of extrusion and high reducibility of H 2 SO 3 . [ 6,15 ] Furthermore, the ash content of corn starches isolated by three methods was also not statistically different ( p > 0.05), which was similar to that of commercial starch. The similar chemical compositions of corn starches isolated by three methods indicated that the quality of starch produced by extrusion‐assisted wet‐milling is the same as that of convention wet‐milling.…”

“…The increase in swelling power and solubility of corn starch isolated by EHS and ELS may be due to the fact that extrusion disrupted the noncovalent bonds between protein and starch, which was beneficial to the combination of water and starch molecules. [ 15,16,20 ]…”

“…The increase in swelling power and solubility of corn starch isolated by EHS and ELS may be due to the fact that extrusion disrupted the noncovalent bonds between protein and starch, which was beneficial to the combination of water and starch molecules. [15,16,20] Corn starch isolated by EHS showed the higher solubility than that of corn starches isolated by ELS and CS. These results revealed that extrusion-assisted wet-milling could promote the leaching of starch granules during swelling.…”

Extrusion of casein and whey protein isolate enhances anti-hardening and performance in high-protein nutrition bars

“…The mechanical shearing caused by extrusion exposes more sulfhydryl groups of protein molecules, leading to oxidation reactions and promoting the formation of disulfide bonds ( Qi & Onwulata, 2011 ). Moreover, with increasing temperature, the mercapto-disulfide bond exchange reaction became more intense, and the content of mercapto decreased, forming new small molecular aggregates ( Su et al, 2021 ).

Fig.

…”