Principles and applications of spectroscopic techniques for evaluating food protein conformational changes: A review

The Effect of Luteolin and Luteoloside on the Secondary Structure of Lysozyme

The changes of lysozyme conformation in the absence and presence of luteolin and luteoloside were investigated by spectral analysis including fluorescence, UV, CD, Raman, and ATR-FTIR, and the biological activity of lysozyme was investigated by lysozyme assay kit. The results showed that the microenvironment hydrophobicity of lysozyme increased and peptide extension decreased with the addition of luteolin or luteoloside. The α-helix of lysozyme might be influenced by luteolin or luteoloside, and its relative content had a significant difference after adding luteolin or luteoloside by the ATR-FTIR method, which was reconfirmed by CD and Raman spectra. The lysozyme activity changed obviously after adding luteolin or luteoloside. All of the conclusions above indicated the active site of lysozyme in the α-helix might be influenced by luteolin and luteoloside.

Structural and rheological changes of texturized mung bean protein induced by feed moisture during extrusion

Mung bean protein isolate was texturized at different feed moisture contents (30.0, 49.3, and 60.0%) at a constant temperature (144.57 °C) to evaluate the changes in protein profile, solubility, thermal, structural (at secondary and tertiary levels) and rheological properties. SDS-PAGE, surface hydrophobicity, circular dichroism, FTIR spectroscopy, and fluorescence analyses revealed protein unfolding, aggregation, and structural rearrangement as a function of feed moisture content. Extrusion at 49.3% feed moisture produced texturized mung bean protein (TMBP) with favourable partial denaturation, the formation of small aggregates, improved solubility, and digestibility with strong gel forming behaviour, whereas 30.0 and 60.0% moisture content resulted in complete protein denaturation, the undesirable formation of large aggregates and weak gels. In conclusion, protein denaturation and formation of aggregates can be controlled by manipulating feed moisture content during extrusion, with 49.3% feed moisture prompting favourable partial denaturation to produce TMBP with desirable qualities for use as a vegetarian-based meat extender.

Phosphorylation modification affects the gelation behavior of alkali-induced duck egg white gels

In this study, sodium tripolyphosphate (STP) and tetrasodium pyrophosphate (TSPP) were utilized to modify duck egg white protein (EWP). The phosphorylated EWP was prepared as egg white gel (EWG) by adding sodium hydroxide. The phosphorus content of EWP reached 2.18 mg/g and 2.07 mg/g with the addition of STP and TSPP, respectively, after 2 h phosphorylation. The average particle size, absolute zeta potential value, and surface hydrophobicity of EWP increased significantly during phosphorylation. FTIR results indicate that phosphorylation reduced the random structure and α-helical content while increasing the content of β-sheets and β-turn. The mechanical and rheological properties of EWG decreased obviously after phosphorylation. A three-dimensional porous network microstructure was formed, and the gel with added TSPP had larger pores. Adding STP and TSPP to EWG weakened its salt and solvent sensitivity. The findings provide a direction for the exploration of gel properties after protein modification.

Antidiabetic Food-Derived Peptides for Functional Feeding: Production, Functionality and In Vivo Evidences

Bioactive peptides released from the enzymatic hydrolysis of food proteins are currently a trending topic in the scientific community. Their potential as antidiabetic agents, by regulating the glycemic index, and thus to be employed in food formulation, is one of the most important functions of these peptides. In this review, we aimed to summarize the whole process that must be considered when talking about including these molecules as a bioactive ingredient. In this regard, at first, the production, purification and identification of bioactive peptides is summed up. The detailed metabolic pathways described included carbohydrate hydrolases (glucosidase and amylase) and dipeptidyl-peptidase IV inhibition, due to their importance in the food-derived peptides research field. Then, their characterization, concerning bioavailability in vitro and in situ, stability and functionality in food matrices, and ultimately, the in vivo evidence (from invertebrate animals to humans), was described. The future applicability that these molecules have due to their biological potential as functional ingredients makes them an important field of research, which could help the world population avoid suffering from several diseases, such as diabetes.

Effects of chitosan grafted phenolic acid coating on microbiological, physicochemical and protein changes of sea bass (Lateolabrax japonicus) during refrigerated storage

This project aimed to evaluate the effects of gallic acid (GA) and protocatechuic acid (PA) grafted onto chitosan (CS) on the improved quality of sea bass (Lateolabrax japonicus) during refrigerated storage. The incorporation of GA and PA onto CS (CS-g-GA and CS-g-PA) were achieved by the carbodiimide-mediated grafting procedure. Samples were treated with different solutions (deionized water [CK], 1% CS [m/v], 1% CS-g-GA [m/v], and 1% CS-g-PA [m/v]) for 10 min, which were then stored at 4 °C. Microbiological quality, including total viable counts (TVC), psychrophilic bacterial counts (PBC), Pseudomonas bacterial counts, and H₂ S-producing bacterial counts were measured. Physicochemical parameters, including pH, total volatile basic nitrogen (TVB-N), thiobarbituric acid (TBA) value, water holding capacity (WHC), and K value, were measured. The changes in protein characteristics, including sulfhydryl groups (SH), Ca²⁺ -ATPase activity, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and tertiary structure of protein were analyzed periodically, along with texture profile analysis (TPA). The results demonstrated that the CS copolymers treatment exhibited better preservation effects. The CS-g-GA and CS-g-PA treatments could significantly inhibit the growth of microorganisms and retard the increase of pH, TVB-N, TBA, WHC, and K-value during refrigerated storage compared with the CK and CS groups. Additionally, the CS-g-GA and CS-g-PA treatments could delay the protein oxidation by keeping a higher SH level and Ca²⁺ -ATPase activity. The CS copolymers treatment could also extend the shelf life for another 6 days compared with that of CK. As a result, CS copolymers can be employed in a promising method for the preservation of sea bass. PRACTICAL APPLICATION: The incorporation of gallic acid and protocatechuic acid onto chitosan (CS-g-GA and CS-g-PA) showed superior antioxidant and antimicrobial activities when applied on sea bass. The CS-g-GA and CS-g-PA coatings could maintain the quality and freshness of refrigerated sea bass. Additionally, this research could provide a theoretical basis for the application of graft copolymers on the preservation of aquatic products.

Antioxidant, Physicochemical, and Cellular Secretion of Glucagon-Like Peptide-1 Properties of Oat Bran Protein Hydrolysates

The aim of this work was to determine the physicochemical and biological activities of hydrolyzed proteins from sonicated oat brans. In addition to the control bran sample, two types of pre-treatment procedures-namely, ultrasonic bath and probe-type sonication-were performed to extract proteins, followed by hydrolysis with various proteases. Physicochemical analyses showed that Flavourzyme-hydrolysates had greater amounts of aromatic amino acids, Papain-hydrolysates low surface charges (-0.78 to -1.32 mV) compared to the others (-3.67 to -9.17 mV), and Alcalase-hydrolysates a higher surface hydrophobicity. The hydrolysates had good radical scavenging activities but, as the ultrasonic pre-treatment of the brans showed, in certain cases there was a reduction in activities of up to 22% for ROO^• and HO^• and 15% for O₂^•- radicals. In anti-diabetic tests, the maximum inhibition of α-amylase was 31.8%, while that of dipeptidyl peptidase-4 was 53.6%. In addition, the secretion of glucagon-like peptide-1 in NCI-H716 cells was enhanced by 11.5% in the presence of hydrolysates.

Effects of ultrasound on functional properties, structure and glycation properties of proteins: a review

Protein is an indispensable part of life. It provides nutrition for human body and flavor for food. The role of protein depends largely on the functional properties of the protein. Therefore, the elucidation of protein structure and functional properties needs to be further explored. The effects of structural and functional properties of proteins under different ultrasonic treatment conditions were reviewed. The structural changes of protein were studied by hydrogen-deuterium exchange mass spectrometry combined with fluorescence spectrometry and proteomics, and the mechanism of action was determined. The glycation site, the glycation degree, and the glycation characteristics of different sugars were determined. The protein was modified by ultrasound, and the influence of protein structure, physicochemical properties, protein glycation characteristics, and the action mechanism were analyzed by biological mass spectrometry.

The specific binding of a new 1,2,3-triazole to three blood proteins and it's appended rhodamine complex for selective detection of Hg2

A synthesized compound, ethyl 2,5-diphenyl-2H-1,2,3-triazole-4- carboxylate (EDTC) was investigated on its physiochemical parameters and structural properties by using the quantum-chemical method. The results on the theoretical spectrum of EDTC were line with experimental fluorescence and absorption spectrum in large degree. Then EDTC was successfully synthesized to a novel rhodamine-based fluorescent probe (REDTC), which showed a distinct fluorescence enhancement upon the presence of Hg²⁺ in dimethyl formamide-water (DMF-H₂O) buffer solution (pH 7.4). Meanwhile, the triazole appended colorless compound turns to pink upon complex formation with Hg²⁺ ions as 1:2 molar ratios and enables naked-eye detection. The chromogenic mechanism was determined by using spectroscopic measurements and TD DFT calculation. The fluorescence imaging experiments of Hg²⁺ in HeLa cell revealed that the probe REDTC could be labeled and it could be used in biological systems. Also, the intermediate EDTC was developed as a sensitive fluorescent probe for specific studies on the interactions to three kinds of blood proteins including human serum albumin (HSA), human immunoglobulin (HIg) and bovine hemoglobin (BHb) by using a series of spectroscopic methods and molecular docking under the simulative physiological conditions. The interactions between EDTC and these proteins led to the distinct fluorescence enhancement. The thermodynamic measured results further suggested that hydrophobic forces play a dominating role in stabilizing the complexes, which are in correspondence with the results from molecular docking. The UV-visible, synchronous, and three-dimensional (3D) fluorescence measurements demonstrated that EDTC influences the conformational of proteins and the microenvironment surrounding HSA, HIg, or BHb in aqueous solution.

Advances in renewable plant-derived protein source: The structure, physicochemical properties affected by ultrasonication

In recent years, there has been increasing interest in renewable and sustainable protein resource of plant origin. The reasons for this are summarized as follows: (1) green, low-cost, environmental friendly and sustainable concepts are deeply rooted in people's minds; (2) long-term use of animal protein can lead to high blood pressure, obesity, negative environmental impacts; (3) more and more vegetarians are emerged; (4) many consumers still do not accept food grade insect. Based on this situation, this paper links eco-innovative ultrasound technology to plant-derived sustainable proteins resource, and magnifies the advantages of both at the same time. Ultrasound is a novel, green and rapid developing environmental friendly technology, which is suitable for up scaling and improving the physicochemical properties of protein. This review summarizes the mechanisms, cavitation properties of ultrasonic field, consumption of energy, applications of spectroscopic techniques for evaluating plant-derived proteins conformation changes, effects of ultrasound on the structure and physicochemical properties of plant-derived renewable proteins, and application of ultrasound treatment proteins in food industry. Furthermore, future research to better utilize this green technology is suggested. In this way, it not only conforms to the concept of sustainable, high-efficiency, and environmental protection of the food protein industry, but also clarifies the relationship between protein structure and properties, which are conducive to the application of ultrasound in protein industrialization.

Ultrasensitive analysis of kanamycin residue in milk by SERS-based aptasensor

An ultrasensitive method for the kanamycin (KANA) detection in milk sample using surface-enhanced Raman spectroscopy-based aptasensor was employed in the current study. Double strand DNA binding bimetallic gold@silver nanoparticles were developed as a sensing platform. Probe DNAs were first embedded on the surface of gold nanoparticles by the end-modified thiol, and after silver shell encapsulating, KANA aptamer DNAs with the Raman reporter Cy3 were then hybridized with probe DNAs by complementary base pairing. Results showed that with increase in the KANA concentration, the Raman intensity of Cy3 decreased. Besides achieving selectivity, an ultralow detection limit of 0.90 pg/mL, a broad linear relationship ranging from 10 μg/mL to 100 ng/mL in aqueous reagent and satisfactory recoveries of 90.4-112% in liquid whole milk were obtained. The result of actual sample proved that this aptasensor was promising in trace determination of KANA residue.

Fabrication of gold nanorods for SERS detection of thiabendazole in apple

Thiabendazole (TBZ) is a kind of pesticide that is widely used in agriculture, and its residue may pose a threat to human health. In order to measure TBZ residues in food samples, a surface-enhanced Raman spectroscopy (SERS) method combined with a homogeneous and reusable gold nanorods (GNR) array substrate was proposed. GNR with a high uniformity was synthesized and then applied to the self-assembly of a GNR vertically aligned array. The relative standard deviation (RSD) of the array for SERS could reach 15.4%, and the array could be reused for more than seven times through the treatment of plasma etching. A logarithmic correlation between TBZ concentration and Raman intensity was obtained, with the best determination coefficient (R²) and the corresponding limit of detection (LOD) of 0.991 and 0.037 mg/L in methanol solution, and 0.980 and 0.06 ppm in apple samples, respectively. The recoveries of TBZ in apple samples ranged from 76% to 107%. This study provided a rapid and sensitive approach for detecting TBZ in apples based on SERS coupled with GNR array substrate, showing great potential for analyzing other trace contaminants in food matrices.