Elucidation of structural changes in soy protein isolate upon heating by Raman spectroscopy

Raman spectroscopy and its plasmon-enhanced counterparts: A toolbox to probe protein dynamics and aggregation

Protein unfolding and aggregation are often correlated with numerous diseases such as Alzheimer's, Parkinson's, Huntington's, and other debilitating neurological disorders. Such adverse events consist of a plethora of competing mechanisms, particularly interactions that control the stability and cooperativity of the process. However, it remains challenging to probe the molecular mechanism of protein dynamics such as aggregation, and monitor them in real-time under physiological conditions. Recently, Raman spectroscopy and its plasmon-enhanced counterparts, such as surface-enhanced Raman spectroscopy (SERS) and tip-enhanced Raman spectroscopy (TERS), have emerged as sensitive analytical tools that have the potential to perform molecular studies of functional groups and are showing significant promise in probing events related to protein aggregation. We summarize the fundamental working principles of Raman, SERS, and TERS as nondestructive, easy-to-perform, and fast tools for probing protein dynamics and aggregation. Finally, we highlight the utility of these techniques for the analysis of vibrational spectra of aggregation of proteins from various sources such as tissues, pathogens, food, biopharmaceuticals, and lastly, biological fouling to retrieve precise chemical information, which can be potentially translated to practical applications and point-of-care (PoC) devices. This article is categorized under: Therapeutic Approaches and Drug Discovery > Emerging Technologies Diagnostic Tools > Diagnostic Nanodevices Nanotechnology Approaches to Biology > Nanoscale Systems in Biology.

Fabrication and characterization of succinylated and glycosylated soy protein isolate and its self-assembled nanogel

In this study, we used succinic anhydride (SA) acylation and dextran (DX) glycosylation modified soybean isolate protein (SPI) to develop self-assembled SPI-SA-DX adduct-based nanogels. Degree of modification, SDS-PAGE, and FT-IR studies showed that the amino group of the SPI was replaced by hydrophilic dextran and succinic acid carboxyl groups. Dextran chain and anhydride group attachment to the soybean protein surface enhanced hydrophilicity and spatial site blocking. Modification-induced protein structure unfolding, free sulfhydryl groups to be converted to disulfide bonds, and reduced surface hydrophobicity (H₀). H₀ was lowest at 33,750 ± 1008.29 when SA content = 10 % protein content (SPI-SA₃-DX). The nanometer gel based on SPI-SA₃-DX had the maximum turbidity and clear transparent solution without precipitation. Its particle size and polymer dispersibility index (PDI) were also the smallest, with values of (106.87 ± 4.51) nm and 0.21 ± 0.009, respectively. Transmission electron microscopy showed that nanogels had subspherical shell-core structures. Nanogels were stable under different pH, ionic strength, high temperature, and storage conditions.

Ultrasound-assisted air-jet spinning of silk fibroin-soy protein nanofiber composite biomaterials

Ultrasound utilizes a non-radiation technology that can meet modern standards to gain access to cheap, reliable and sustainable modern energy. Ultrasound technology can be implemented in the field of biomaterials for its exceptional potential in controlling the shape of nanomaterials. This study presents the first example of the production of soy and silk fibroin protein composite nanofibers in various ratios via combining ultrasonic technology with air-spray spinning. Characterization of ultrasonic spun nanofibers was performed by scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetric (TG) analysis, water contact angle, water retention, enzymatic degradation, and cytotoxicity assays. The effects that adjustments on the ultrasonic time have on the surface morphology, structures, thermal properties, hydrophilicity, water-uptake, bio-enzyme degradability, mechanical properties, and cytocompatibility of the material were examined. It was discovered that as the sonication time increased from 0 to 180 min, the beading phenomenon disappeared, forming nanofibers with uniform diameter and porosity; while the content of β-sheet crystals in the composites and their thermal stability gradually increased, the materials glass transition temperature decreased, and preferred mechanical properties were obtained. Additional studies show that the hydrophilicity, water retention capacity and enzymatic degradation rate were also enhanced by ultrasound, providing a favorable environment for cell attachment and proliferation. This study highlights the experimental and theoretical methods for ultrasound assisted air-jet spinning of biopolymer nanofibrous materials with tunable properties and high biocompatibility, which provide a wide range of applications in wound dressings and drug-carrying systems. This work shows great potential for a direct road to sustainable development of protein based fibers in the industry, thus promoting economic growth, and improving the health of the general population and well-being of wounded patients worldwide.

Solubility and conformational characterization of rice glutelin after high temperature treatment

Enhancing the solubility of rice glutelin in neutral aqueous solution is the prerequisite for the development of rice protein drinks and ingredients. Herein, glutelin was first dissolved in an aqueous solution of pH 12, and then heated at 121 °C for 20 min. The results showed that the solubility of glutelin increased from 2.55 mg/mL to 20.7 mg/mL at pH 7. The size of glutelin aggregates at pH 7 decreased from 900 nm to 400 nm after high temperature treatment (HTT), which was confirmed by atomic force microscopy. The results of small angle X-ray scattering showed that HTT induced the conformational unfolding of glutelin, and the protein in the aggregate was rod like shape as well as the mean square rotation radius decreased from 64.9 to 54.8 Å. Furthermore, Raman spectrum results also agree with the unfolding of glutelin conformation, which was mainly reflected in the changes of tyrosine and tryptophan residues, as well as the decreasing of α-helix content and increasing of β-sheet content. After being freeze-dried, HTT glutelin has a re-solubilization capacity of 15.48 mg/mL in pH 7 aqueous solution, which was superior to that of spray dried glutelin powder (pH 7, 9.19 mg/mL).

Conformational Changes in Proteins Caused by High-Pressure Homogenization Promote Nanoparticle Formation in Natural Bone Aqueous Suspension

As a natural calcium resource, animal bone needs to be miniaturized to the nanoscale to improve palatability and absorption capacity. To explore the mechanism of high-pressure homogenization (HPH) in preparing natural bone aqueous nanosuspensions, the relationships between the changes in protein conformation, solubility and quality characteristics of rabbit bone aqueous suspensions (RBAS) prepared by different HPH cycles were studied. The results showed that the improvements in particle size, stability and calcium solubility of RBASs could be mainly attributed to the improvement of protein solubility induced by the changes in protein conformation. HPH treatment led to the denaturation and degradation of protein in rabbit bone, generating soluble peptides and improving the stability of the suspensions by enhancing the surface charge of the particles. When collagen as the main protein was partially degraded, the hydroxyapatite in the bone was crushed into tiny particles. The increase in the particle-specific surface area led to the release of calcium ions, which chelated with the peptides to produce peptide calcium. However, excessive HPH treatment caused the production of protein macromolecular aggregates and affected the quality of RBASs. This study is helpful to promote the application of HPH technology in animal bone nanoprocessing.

Plant protein-based fibers: Fabrication, characterization, and potential food applications

Proteins from plants have been considered as safer, healthier, and more sustainable resources than their animal counterparts. However, incomplete amino acid composition and relatively poor functionality limit their applications in foods. Structuring plant proteins to fibrous architectures enhances their physicochemical properties, which can favor various food applications. This review primarily focuses on fabrication of fibers from plant proteins via self-assembly, electrospinning, solution blow spinning, wet spinning, and high-temperature shear, as well as on several applications where such fibrous proteins assemble in quality foods. The changes of protein structure and protein-protein interactions during fiber production are discussed in detail, along with the effects of fabrication conditions and protein sources on the morphology and function of the fibers. Self-assembly requires proteolysis and subsequent peptide aggregation under specific conditions, which can be influenced by pH, salt and protein type. The spinning strategy is more scalable and produces uniformed fibers with larger length scales suitable for encapsulation, food packaging and sensor substrates. Significant progress has been made on high-temperature shear (including extrusion)-induced fibers responsible for desirable texture in meat analogues. Structuring plant proteins adds values for broadened food applications, but it remains challenging to keep processes cost-effective and environmentally friendly using food grade solvents.

Microstructural Analysis of Whey/Soy Protein Isolate Mixed Gels Using Confocal Raman Microscopy

This work explores the potential of confocal Raman microscopy to investigate the microstructure of mixed protein gel systems. Heat-set protein gels were prepared using whey protein isolate (WPI), soy protein isolate (SPI), and mixtures thereof, with a total of five different whey-to-soy protein ratios (100, 75, 50, 25, and 0%). These were analysed using confocal Raman microscopy, and different data analysis approaches were used to maximize the amount of structural and compositional information extracted from the spectral datasets generated, including both univariate and multivariate analysis methods. Small spectral differences were found between pure WPI and SPI gels, mainly attributed to conformational differences (amide bands), but SPI exhibited considerably greater auto-fluorescence than WPI. The univariate analysis method allowed for a rapid microstructural analysis, successfully mapping the distribution of protein and water in the gels. The greater fluorescence of the capsule-like structures found in the mixed gels, compared to other regions rich in proteins, suggested that these may be enriched in soy proteins. Further analysis, using a multivariate approach, allowed us to distinguish proteins with different levels of hydration within the gels and to detect non-proteinaceous compounds. Raman microscopy proved to be particularly useful to detect the presence of residual lipids in protein gels.

Development and Characterization of Weft-Knitted Fabrics of Naturally Occurring Polymer Fibers for Sustainable and Functional Textiles

This study focuses on the potential uses in textiles of fibers of soy protein (SP) and chitin, which are naturally occurring polymers that can be obtained from agricultural and food processing by-products and wastes. The as-received natural fibers were first subjected to a three-step manufacturing process to develop yarns that were, thereafter, converted into fabrics by weft knitting. Different characterizations in terms of physical properties and comfort parameters were carried out on the natural fibers and compared to waste derived fibers of coir and also conventional cotton and cotton-based fibers, which are widely used in the textile industry. The evaluation of the geometry and mechanical properties revealed that both SP and chitin fibers showed similar fineness and tenacity values than cotton, whereas coir did not achieve the expected properties to develop fabrics. In relation to the moisture content, it was found that the SP fibers outperformed the other natural fibers, which could successfully avoid variations in the mechanical performance of their fabrics as well as impair the growth of microorganisms. In addition, the antimicrobial activity of the natural fibers was assessed against different bacteria and fungi that are typically found on the skin. The obtained results indicated that the fibers of chitin and also SP, being the latter functionalized with biocides during the fiber-formation process, showed a high antimicrobial activity. In particular, reductions of up to 100% and 60% were attained for the bacteria and fungi strains, respectively. Finally, textile comfort was evaluated on the weft-knitted fabrics of the chitin and SP fibers by means of thermal and tactile tests. The comfort analysis indicated that the thermal resistance of both fabrics was similar to that of cotton, whereas their air permeability was higher, particularly for chitin due to its higher fineness, which makes these natural fibers very promising for summer clothes. Both the SP and chitin fabrics also presented relatively similar values of fullness and softness than the pure cotton fabric in terms of body feeling and richness. However, the cotton/polyester fabric was the only one that achieved a good range for uses in winter-autumn cloths. Therefore, the results of this work demonstrate that non-conventional chitin and SP fibers can be considered as potential candidates to replace cotton fibers in fabrics for the textile industry due to their high comfort and improved sustainability. Furthermore, these natural fibers can also serve to develop novel functional textiles with antimicrobial properties.

Comprehensive overview of the quality of plant- And animal-sourced proteins based on the digestible indispensable amino acid score

Indispensable amino acid (IAA) composition and standardized ileal digestibility (SID) of five animal- and 12 plant-based proteins were used to calculate their respective Digestible Indispensable Amino Score (DIAAS) according to the three age categories defined by the Food and Agriculture Organization (FAO). Mean IAA content and mean SID obtained from each protein dataset were subsequently used to simulate optimal nutritional quality of protein mixtures. Datasets revealed considerable variation in DIAAS within the same protein source and among different protein sources. Among the selected protein sources, and based on the 0.5- to 3-year-old reference pattern, pork meat, casein, egg, and potato proteins are classified as excellent quality proteins with an average DIAAS above 100. Whey and soy proteins are classified as high-quality protein with an average DIAAS ≥75. Gelatin, rapeseed, lupin, canola, corn, hemp, fava bean, oat, pea, and rice proteins are classified in the no quality claim category (DIAAS <75). Potato, soy, and pea proteins can complement a broad range of plant proteins, leading to higher DIAAS when supplied in the form of protein mixtures and at specific ratios. Such complementarity highlights the potential to achieve an optimal nutritional efficiency with plant proteins alone.

Characterization of mammalian cell culture raw materials by combining spectroscopy and chemometrics

Two of the primary issues with characterizing the variability of raw materials used in mammalian cell culture, such as wheat hydrolysate, is that the analyses of these materials can be time consuming, and the results of the analyses are not straightforward to interpret. To solve these issues, spectroscopy can be combined with chemometrics to provide a quick, robust and easy to understand methodology for the characterization of raw materials; which will improve cell culture performance by providing an assessment of the impact that a given raw material will have on final product quality. In this study, four spectroscopic technologies: near infrared spectroscopy, middle infrared spectroscopy, Raman spectroscopy, and fluorescence spectroscopy were used in conjunction with principal component analysis to characterize the variability of wheat hydrolysates, and to provide evidence that the classification of good and bad lots of raw material is possible. Then, the same spectroscopic platforms are combined with partial least squares regressions to quantitatively predict two cell culture critical quality attributes (CQA): integrated viable cell density and IgG titer. The results showed that near infrared (NIR) spectroscopy and fluorescence spectroscopy are capable of characterizing the wheat hydrolysate's chemical structure, with NIR performing slightly better; and that they can be used to estimate the raw materials' impact on the CQAs. These results were justified by demonstrating that of all the components present in the wheat hydrolysates, six amino acids: arginine, glycine, phenylalanine, tyrosine, isoleucine and threonine; and five trace elements: copper, phosphorus, molybdenum, arsenic and aluminum, had a large, statistically significant effect on the CQAs, and that NIR and fluorescence spectroscopy performed the best for characterizing the important amino acids. It was also found that the trace elements of interest were not characterized well by any of the spectral technologies used; however, the trace elements were also shown to have a less significant effect on the CQAs than the amino acids. © 2017 The Authors Biotechnology Progress published by Wiley Periodicals, Inc. on behalf of American Institute of Chemical Engineers, 33:1127-1138, 2017.

Characterization of swiftlet edible bird nest, a mucin glycoprotein, and its adulterants by Raman microspectroscopy

Edible bird's nest (EBN) is made from the glutinous salivary secretion of highly concentrated mucin glycoprotein by swiftlets (genus Aerodramus or Collocalia) native to the Indo-Pacific region. The unique Raman spectrum of EBN has vibrational lines that can be assigned to peptides and saccharides in the glycoprotein, and it can be used to screen for adulteration. The common edible adulterants classified into two types. Type I adulterants, such as fish bladder, pork skin, karaya gum, coralline seaweed, agar strips, and tremella fungus, were solids which adhered externally on the surface of the EBN cement. They can usually be detected with a microscope based on differences in the surface structure. Type II adulterants were water soluble substances such as saccharides (e.g., glucose, sucrose), polypeptides (e.g., hydrolyzed collagen) and salts (e.g. monosodium glutamate) which can be readily soaked up by the EBN hydrogel when moist and adsorbed internally in the EBN cement matrix forming a composite upon drying, making them difficult to detect visually. The present study showed that Raman microspectroscopy offers a rapid, non-invasive, and label free technique to detect both Type I and II adulterants in EBN.

Secondary Structure and Subunit Composition of Soy Protein In Vitro Digested by Pepsin and Its Relation with Digestibility

In the present study, in vitro digestibility and structure of soybean protein isolates (SPIs) prepared from five soybean varieties were investigated in simulated gastric fluid (SGF), using FT-IR microspectroscopy and SDS-PAGE. The result indicated that β-conformations were prone to be hydrolyzed by pepsin preferentially and transformed to unordered structure during in vitro digestion, followed by the digestion of α-helix and unordered structure. A negative linear correlation coefficient was found between the β-conformation contents of five SPIs and their in vitro digestibility values. The intensities of the protein bands corresponding to 7S and 11S fractions were decreased and many peptide bands appeared at 11~15 kDa during enzymatic hydrolysis. β-conglycinin was poorly hydrolyzed with pepsin, especially the β-7S subunit. On the other hand, basic polypeptides of glycinin degraded slower than acidic polypeptides and represented a large proportion of the residual protein after digestion. 11S-A₃ of all SPIs disappeared after 1 h digestion. Moreover, a significant negative linear correlation coefficient (r = −0.89) was found between the β-7S contents of five SPIs and their in vitro digestibility values. These results are useful for further studies of the functional properties and bioactive properties of these varieties and laid theoretical foundations for the development of the specific functional soy protein isolate.

Structural Changes in Rice Bran Protein upon Different Extrusion Temperatures: A Raman Spectroscopy Study

Raman spectroscopy is critically evaluated to establish the limits to which it may be used to detect changes in protein conformation upon extrusion. Rice bran protein (RBP) extruded with different temperatures (100, 120, 140, and 160°C, labeled as ERBP-) was considered. DSC showed that extrusion at 100°C increasedTDof RBP but decreased itsΔH, while, after extrusion treatment at 120°C, RBP completely denatured. A progressive increase in unordered structure and a general decrease inα-helix structure andβ-sheet structure of extruded RBP were observed from Raman study. Meanwhile the content of unordered structure increased up to 140°C and then decreased at 160°C, while the trend ofα-helix andβ-sheet content was opposite, which was contributed to the composite effect of formation of some more protein aggregation and protein denaturation. Extrusion generally induced a significant decrease in Trp band near 760 cm−1but an increase at 160°C. No significant difference was observed in Tyr doublet ratios between controlled RBP samples and extruded RBP below 160°C, whereas Tyr doublet ratios of extruded RBP decreased at 160°C. Intensity of the band assigned toCHnbending decreased progressively and then increased as extrusion temperature increased, indicating changes in microenvironment and polarity.

Effect of potential on temperature-dependent SERS spectra of neuromedin B on Cu electrode

Adsorption of decapeptide neuromedin B (NMB) on copper electrode has been investigated by in situ surface-enhanced Raman scattering (SERS) spectroelectrochemistry in the temperature interval from 12 to 72 °C at -0.600 and -1.000 V potentials. It was found that intensities of peptide bands decrease at temperatures above 30 °C with higher decrease slope at -1.000 V. Frequency of F12 mode (1004 cm(-1)) of non-surface-interactive phenylalanine residue was found to be insensitive to temperature variation at both studied electrode potentials, while frequency-temperature curves for surface-interactive groups (Amide-III, methylene) were found to be controlled by the potential. In particular, opposite frequency-temperature trends were detected for Amide-III (Am-III) mode indicating decrease in H-bonding interaction strength of amide C[double bond, length as m-dash]O and N-H groups above 38 °C for -0.600 V, and increase in H-bonding interaction strength between 12 and 72 °C for -1.000 V. Anomalous Am-III temperature-dependence of the frequency at -1.000 V was explained by temperature-induced transformation of a disordered secondary structure to a helix-like conformation. The potential-difference spectrum revealed interaction of methylene groups with Cu surface at sufficiently negative potential values because of the appearance of a soft C-H stretching band near 2825 cm(-1) and a broad band near 2904 cm(-1) assigned to vibration of a distal C-H bond of the surface-confined methylene group. Consequently, a rapid decrease in frequency of CH(2)-stretching band with temperature was observed at -1.000 V, while no essential frequency changes were detected for this mode at -0.600 V. The results show that electrode potential controls the temperature-dependence of the frequency for vibrations associated with surface-interactive molecular groups.

Raman spectroscopy and multivariate analysis for the rapid discrimination between native-like and non-native states in freeze-dried protein formulations

This study investigates whether Raman spectroscopy combined with multivariate analysis (MVA) enables a rapid and direct differentiation between two classes of conformational states, i.e., native-like and non-native proteins, in freeze-dried formulations. A data set comprising of 99 spectra, both from native-like and various types of non-native freeze-dried protein formulations, was obtained by freeze-drying lactate dehydrogenase (LDH) as model protein under various conditions. Changes in the secondary structure in the solid freeze-dried proteins were determined through visual interpretation of the blank corrected second derivative amide I band in the ATR-FTIR spectra (further called FTIR spectra) and served as an independent reference to assign class labels. Exploratory analysis and supervised classification, using Principal Components Analysis (PCA) and Partial Least Squares - Linear Discriminant Analysis (PLS-LDA), respectively, revealed that Raman spectroscopy is with 95% accuracy able to correctly discriminate between native-like and non-native states in the tested freeze-dried LDH formulations. Backbone (i.e., amide III) and side chain sensitive spectral regions proved important for making the discrimination between both classes. As discrimination was not influenced by the spectral signals from the tested excipients, there was no need for blank corrections. The Raman model may allow direct and automated analysis of the investigated quality attribute, opening possibilities for a real time and in-line quality indication as a future step. However, the sensitivity of the method should be further investigated and where possible improved.