Structural Rearrangement of Ethanol-Denatured Soy Proteins by High Hydrostatic Pressure Treatment

Abstract

The effects of high hydrostatic pressure (HHP) treatment (100-500 MPa) on solubility and structural properties of ethanol (EtOH)-denatured soy β-conglycinin and glycinin were investigated using differential scanning calorimetry, Fourier transform infrared and ultraviolet spectroscopy. HHP treatment above 200 MPa, especially at neutral and alkaline pH as well as low ionic strength, significantly improved the solubility of denatured soy proteins. Structural rearrangements of denatured β-conglycinin subjected to high pressure were confirmed, as evidenced by the increase in enthalpy value (ΔH) and the formation of the ordered supramolecular structure with stronger intramolecular hydrogen bond. HHP treatment (200-400 MPa) caused an increase in surface hydrophobicity (F(max)) of β-conglycinin, partially attributable to the exposure of the Tyr and Phe residues, whereas higher pressure (500 MPa) induced the decrease in F(max) due to hydrophobic rearrangements. The Trp residues in β-conglycinin gradually transferred into a hydrophobic environment, which might further support the finding of structural rearrangements. In contrast, increasing pressure induced the progressive unfolding of denatured glycinin, accompanied by the movement of the Tyr and Phe residues to the molecular surface of protein. These results suggested that EtOH-denatured β-conglycinin and glycinin were involved in different pathways of structural changes during HHP treatment.

Physicochemical properties of soy protein prepared by enzyme‐assisted countercurrent extraction

“…Differential scanning calorimetry (DSC) has been widely used to characterise the thermal transition properties of soy protein, containing β‐conglycinin and glycinin (Wang et al ., ; Shen & Tang, ). In the DSC profiles of soy proteins, two endothermic peaks with peak transition temperatures ( T d ) of about 70 and 90 °C were clearly corresponded to thermal denaturation of β‐conglycinin and glycinin polypeptides, respectively.…”

“…Table summarises surface hydrophobicity parameters ( F max , K d and PSH) of different extraction methods. In the case of AP and AP‐DEN, there was no a significant ( P < 0.05) difference in PSH, defined as the number and affinity of hydrophobic sites, suggesting similar surface hydrophobicity although the significant ( P < 0.05) increases in F max and K d were observed (Wang et al ., , ). These results indicated the generation of new binding sites on the protein's surface for ANS and the decrease in the binding affinity of ANS to AP‐DEN.…”

“…The thermal transition of various protein samples was assessed using a TA Q100-DSC thermal analyser (TA Instruments, USA) according to the method of Wang et al (2011). Protein samples (2.0 mg) were weighed into aluminium liquid pans, and 10 lL of 10 mM phosphate buffer (pH 7.0) was added.…”

“…The surface hydrophobicity of samples was assessed by titration with ANS according to the method of Wang et al (2011). Protein solution (1 mL, 0.2 mg mL À1 ) was placed in the cell of a fluorescence spectrophotometer (F7000, Hitachi Co., Japan).…”

“…In terms of protein flavour, alcohol leaching could effectively remove residual polar lipids of protein (Wu et al ., ). However, this process could inevitably result in the loss of protein solubility due to alcohol‐induced denaturation (Wang et al ., ). Based on these considerations, avoiding acid precipitation during protein preparation may be another proper choice.…”