XRD, SEM, and XPS Analysis of Soybean Protein Powders Obtained Through Extraction Involving Reverse Micelles

Abstract

Soybean protein powders obtained by aqueous buffer and reverse micelle extractions were examined and characterized using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and scanning electron microscopy (SEM). These analysis methods provided detailed information about elemental distributions, surface structure, and secondary and microstructures of the protein, respectively. XPS data revealed that the O and N atomic percentages of soybean protein surfaces obtained with bis(2-ethylhexyl) sodium sulfosuccinate (AOT)/hexane reverse micelles were higher than those obtained with aqueous buffer, whereas the percentage of atomic C was lower. The ratios of nitrogen to carbon (N/C) on the surface of soybean protein obtained through the two extraction methods were similar. The O/C ratio for soybean protein obtained from AOT reverse micelles was large. The obtained results indicated that the reverse micelles could affect the C, O, and N components on the surface of soybean proteins. Moreover, XRD and SEM results also showed the influence of AOT reverse micelles, which lead to more β-sheet and pore structures.

Surface Characterization of Cottonseed Meal Products by SEM, SEM-EDS, XRD and XPS Analysis

“…Their particle size distribution was also not as homogenous as the soy protein powder. Indeed, the morphology of the soy protein powders was not like those reported in Zhao et al (2015), rather than spray-dried milk protein concentrates with attached spherical shape protein on the surface (Kelly et al, 2015). The difference in these observations could be attributed to the fact that both protein concentrations and treatment procedures could have affected the morphology of protein products.…”

“…There were two obvious peaks at 2θ of about 9.4 and 20⁰ in the XRD pattern of the four protein samples. These features are typical for soy protein powders, reflecting the α-helix and β-sheet structures of protein molecules, respectively (Chen et al, 2013;Luo et al, 2016;Zhao et al, 2015). The intensity of both peaks was in the order CSPa < CSPI < CSPa, indicating that the two-step fractionation unequally delivered less α-helix and β-sheet protein components into water-soluble fraction than alkali-soluble fraction.…”

“…The different values were apparently due to the fact that the total elemental composition detected by the two methods was not the same. The different surface layers detectable might also play a role in the difference such as XPS determined the elemental composition of the outmost surface layer (6 nm depth) of the protein samples (Zhao et al, 2015).…”

“…surface properties of protein are related with its numerous functional properties in practical utilization, such as wetting, dispersion, oxidative stability, flowability and rehydration properties Nawaz et al, 2016;Zhao et al, 2011). Zhao et al (2015) reported that soy protein powder made by reverse micelle extraction showed more -sheet and pore structures than that extracted by aqueous buffer extraction. The reverse micelles extraction was further shown to affect the C, O and N components on the surface of walnut protein powder .…”

“…Therefore, the objective of the present study was to characterize the surface properties of six cottonseed meal products using scanning electron microscopy (SEM), scanning electron microscopy-energy dispersive spectrometer (SEM-EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). For comparison, a commercially available soy protein flour was also examined in the same way as relevant information is available for soy protein powders (Chen et al, 2013;Zhao et al, 2015;. Characterization of surface properties would enhance their potential utilization for various agro-based and industrial purposes.s.…”