Evaluation of antioxidant modification on the functional and structural properties of EWP conjugates

Development of faba protein-tannic acid conjugate via free radical grafting: Evaluation of interaction mechanisms and antioxidative properties

A soluble fraction of faba bean protein was conjugated with tannic acid via the free-radical grafting method using a mixture of ascorbic acid and hydrogen peroxide. Surface plasmon resonance showed a strong bonding between them, while the free amino and thiol group measurements indicated tannic acid's bonding with the amino groups and cysteine residues on the proteins. Structural analysis using intrinsic fluorescence and surface hydrophobicity demonstrated tannic acid's interaction with the aromatic and hydrophobic amino acids of the protein. The conjugate showed about 77 % DPPH, 89 % ABTS, and 83 % hydroxyl radical scavenging activities and superior ferric-reducing ability compared to the protein alone and the mixture of protein and tannic acid. Electron paramagnetic resonance (EPR) spectroscopy revealed 97.8 % radical scavenging ability of the conjugate, comparable to the pure tannic acid. The exceptional antioxidative properties of conjugate can be utilized to delay lipid oxidation in protein-stabilized oil-in-water emulsions.

Epigallocatechin gallate modification of physicochemical, structural and functional properties of egg yolk granules

The aim of this study was to prepare protein-polyphenol covalent complexes by treating egg yolk granules (EYG) with alkali in the presence of epigallocatechin gallate (EGCG) and characterize the physicochemical, structural, and functional properties of these covalent complexes. Results revealed that the optimal covalent binding occurred when the concentration of EGCG reached 0.15% (w/w), resulting in a grafting rate of 1.51 ± 0.03%. As the amount of EGCG increased, corresponding increases were observed in the particle size and ζ-potential of the complexes, thereby enhancing their stability. Furthermore, our analysis using fluorescence spectroscopy, FTIR, SEM, and SDS-PAGE collectively demonstrated the formation of a covalent complex between EYG and EGCG. Notably, the covalent complexes exhibited improved antioxidant activity and emulsifying properties. Overall, this study establishes a theoretical framework for the future practical application of EYG, emphasizing the potential of EGCG to modify its structural and functional characteristics.

Conjugation of lesser mealworm (Alphitobius diaperinus) larvae protein with polyphenols for the development of innovative antioxidant emulsifiers

Lesser mealworm protein concentrate (LMPC) was conjugated with chlorogenic acid (CA) or tannic acid (TA) using an alkaline method. The impact of polyphenol type and concentration on the physicochemical and structural characteristics, antioxidant, interfacial, and emulsifying properties of the LMPC-polyphenol conjugates were investigated. Under the conditions tested, TA demonstrated higher affinity for LMPC compared to CA. The conjugation of LMPC induced conformational changes as showed by intrinsic fluorescence and FT-MIR raw spectra analysis. The surface hydrophobicity of the conjugates was reduced, leading to increased interfacial tension values for LMPC-TA conjugates without impairment of the emulsifying activity. The antioxidant properties were significantly improved by the conjugation. Flaxseed oil-in-water (O/W) emulsions stabilized by the conjugates and LMPC remained physically stable for 12 days at 50 °C with a notable reduction of secondary oxidation products when conjugates were used. LMPC-TA and LMPC-CA exhibited potential to be used as novel antioxidant emulsifiers in O/W emulsions.

Antioxidant Activities of Dihydromyricetin Derivatives with Different Acyl Donor Chain Lengths Synthetized by Lipozyme TL IM

Dihydromyricetin (DHM) is a phytochemical with multiple bioactivities. However, its poor liposolubility limits its application in the field. In this study, DHM was acylated with different fatty acid vinyl esters to improve its lipophilicity, and five DHM acylated derivatives with different carbon chain lengths (C2-DHM, C4-DHM, C6-DHM, C8-DHM, and C12-DHM) and different lipophilicity were synthesized. The relationship between the lipophilicity and antioxidant activities of DHM and its derivatives was evaluated with oil and emulsion models using chemical and cellular antioxidant activity (CAA) tests. The capacity of DHM derivatives to scavenge 1,1-diphenyl-2-picrylhydrazyl radical (DPPH•) and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) radical (ABTS+•) was similar to that of DHM, except for C12-DHM. The antioxidant activity of DHM derivatives was lower than that of DHM in sunflower oil, while C4-DHM exhibited better antioxidant capacity in oil-in-water emulsion. In CAA tests, C8-DHM (median effective dose (EC₅₀) 35.14 μmol/L) exhibited better antioxidant activity than that of DHM (EC₅₀: 226.26 μmol/L). The results showed that in different antioxidant models, DHM derivatives with different lipophilicity had various antioxidant activities, which has guiding significance for the use of DHM and its derivatives.

Influence of environmental pH on the interaction properties of WP-EGCG non-covalent nanocomplexes

BACKGROUND

Whey protein-epigallocatechin gallate (WP-EGCG) covalent conjugates and non-covalent nanocomplexes were prepared and compared using Fourier-transform infrared spectra. The effect of pH (at 2.6, 6.2, 7.1, and 8.2) on the non-covalent nanocomplexes' functional properties and the WP-EGCG interactions were investigated by studying antioxidant activity, emulsification, fluorescence quenching, and molecular docking, respectively.

RESULTS

With the formation of non-covalent and covalent complexes, the amide band decreased; the -OH peak disappeared; the antioxidant activity of WP-EGCG non-covalent complexes was 2.59- and 2.61-times stronger than WP-EGCG covalent conjugates for 1-diphenyl-2-picryl-hydrazyl (DPPH) and ferric reducing ability of plasma (FRAP), respectively (particle size: 137 versus 370 nm). The antioxidant activity (DPPH 27.48-44.32%, FRAP 0.47-0.63) was stronger at pH 6.2-7.1 than at pH 2.6 and pH 8.2 (DPPH 19.50% and 26.36%, FRAP 0.39 and 0.41). Emulsification was highest (emulsifying activity index 181 m²  g^-1 , emulsifying stability index 107%) at pH 7.1. The interaction between whey protein (WP) and EGCG was stronger under neutral and weakly acidic conditions: K_SV (5.11-8.95 × 10²  L mol^-1 ) and K_q (5.11-8.95 × 10¹⁰  L mol s^-1 ) at pH 6.2-7.1. Binding constants (pH 6.2 and pH 7.1) increased with increasing temperature. Molecular docking suggested that hydrophobic interactions played key roles at pH 6.2 and pH 7.1 (∆H > 0, ∆S > 0). Hydrogen bonding was the dominant force at pH 2.6 and pH 8.2 (∆H < 0, ∆S < 0).

CONCLUSION

Environmental pH impacted the binding forces of WP-EGCG nanocomplexes. The interaction between WP and EGCG was stronger under neutral and weakly acidic conditions. Neutral and weakly acidic conditions are preferable for WP-EGCG non-covalent nanocomplex formation. © 2023 Society of Chemical Industry.

Evaluation of crossing-linking sites of egg white protein-polyphenol conjugates: Fabricated using a conventional and ultrasound-assisted free radical technique

There has been strong interest in developing effective strategies to inhibit lipid oxidation in emulsified food products such as ω-3 fatty acids, carotenoids, or carotenoids. Dual-functional protein emulsifiers with antioxidant and emulsifying properties are in the spotlight. Our aim was to investigate the influence of caffeic acid (CF), chlorogenic acid (CA) with a C3-C6 structure, epigallocatechin gallate (EGCG), catechin (CT), and quercetin (QE) with a C6-C3-C6 structure on the cross-linking sites and structure of egg white protein (EWP)-polyphenol conjugates fabricated by the free radical method under conventional water bath (WB) and ultrasound assisted (US) conditions. Results of structural analysis and liquid chromatography-tandem mass spectrometry indicated that the structure of EWP-polyphenol conjugates and the cross-linking sites of the two are influenced by the polyphenol structure and the free radical system. Our study provides important information about the mechanism of research into proteins and polyphenols using the free radical method.

Soluble Aggregates of Myofibrillar Proteins Engineered by Gallic Acid: Colloidal Structure and Resistance to In Vitro Gastric Digestion

Myofibrillar protein (MP)-soluble aggregates can be made by tactics of gallic acid (GA) modification during pH shifting, and this work aimed to disclose their aggregation pattern and in vitro digestion behavior. GA modification dissociated the filamentous structure of myofibrils and caused structural reassembly to form small-sized aggregates. These aggregates were evidenced to contain GA-bridged dimers and oligomers of myosin or actin, having a molecular weight of ∼1225 kDa. Additionally, the structural rearrangement significantly decreased the surface hydrophobicity while substantially increased the surface charge. As a result, the obtained colloidal solution was translucent and heat-resistant. Intriguingly, MP-soluble aggregates exhibited a retarded digestive behavior. Further evaluation by a quartz crystal microbalance suggested that the reduced binding affinity of soluble aggregates toward gastric pepsin could be the underlying reason. This work may foster the engineering advances of modulating the MP structure-digestion for the tailor manufacturing of muscle protein-based beverages.

Correlation Analysis of Antioxidant Activities with Tannin, Total Flavonoid, and Total Phenolic Contents of Nutmeg (Myristica fragrans Houtt) Fruit Precipitated by Egg white

The nutmeg (Myristica fragrans) flesh extract has a strong antioxidant activity. Therefore, M. fragrans flesh can be developed for functional drinks which are sources rich in antioxidants good for the prevention and treatment of diseases such as cancer and cardiovascular diseases. However, the tannins' content can cause a bitter and sour taste. Therefore, the tannins content should be reduced by the addition of egg white. The purpose of this study is to find out the comparison of antioxidant activity between a combination of M. fragrans flesh extract with various concentrations of egg white and to correlate its antioxidant activities with tannin, total flavonoid, and total phenolic contents. The antioxidant activities were conducted on M. fragrans flesh extract by using DPPH and ABTS radicals. Tannin, total flavonoid, and total phenolic contents from M. fragrans flesh extract were also tested. The M. fragrans flesh extracts without addition egg white have a strong antioxidant in scavenging the stable free radical ABTS (89.980±0.480 µg/mL) and intermediate antioxidant in scavenging the stable free radical DPPH (105.669±0.102 µg/mL). It is followed accordingly by tannin, total flavonoid, and total phenolic contents, namely 14.034±0.100 %w/w TAE, 26.929±0.129 %w/w QE, and 53.164±0.129 %w/w GAE, respectively. Correlation of tannin, total flavonoid, and total phenolic contents, which inhibited DPPH and ABTS radicals had R2 values of about 89.23-97.63%. It showed that antioxidant activity is strongly influenced by the tannin, total flavonoid, and total phenolic contents. Therefore, precipitation from the tannin-protein bond caused antioxidant activities were decreased.

Conjugation of (-)-epigallocatechin-3-gallate and protein isolate from large yellow croaker (Pseudosciaena crocea) roe: improvement of antioxidant activity and structural characteristics

BACKGROUND

Large yellow croaker (Pseudosciaena crocea) roe is the main by-product in the processing of large yellow croaker. Previous studies have found that its protein isolates are composed of vitellogenin, as well as vitellogenin B and C, having good functional properties. (-)-Epigallocatechin-3-gallate (EGCG) is a natural antioxidant component that can be combined with protein to improve antioxidant activity and structural characteristics of protein.

RESULTS

EGCG was bound with the P. crocea roe protein isolate (pcRPI) by the free radical method to prepare the conjugate. The formation of pcRPI-EGCG conjugates was confirmed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and gel permeation chromatography, which showed that the calculated weight-average molar masses of native-pcRPI and pcRPI-EGCG conjugates were 86.9 and 215.3 kDa, respectively. The results of fluorescence, ultraviolet, circular and infrared spectra indicated that the conjugation of EGCG with native-pcRPI changed the secondary and tertiary structure of native-pcRPI. The pcRPI-EGCG conjugates exhibited higher thermal stability than native-pcRPI. The radical scavenging and reducing power of native-pcRPI were increased by 2.0-2.5- and 1.4-fold, respectively, after the EGCG-grafting reaction.

CONCLUSION

These results indicate that the binding of pcRPI and EGCG effectively improved the antioxidant properties and structural characteristics of the pcRPI. © 2021 Society of Chemical Industry.

Protein-polyphenol conjugates: Preparation, functional properties, bioactivities and applications in foods and nutraceuticals

Protein is a crucial nutritional ingredient in the daily human diet. Polyphenols (PPNs) are the abundant phytochemicals in plants, which are associated with health promotion as well as affect functionality in food systems. Both ingredients possess different types of functionalities (crosslinking, gelling, emulsifying, film-forming, etc.) and bioactivities (antioxidant, antimicrobial, anti-inflammatory, etc.). In the past decade, various methods have been implemented to enhance the functionalities and bioactivities of foods. Conjugation or grafting methods has been introduced widely. Conjugations of PPNs with proteins through various methods have been performed for the synthesis of the protein-polyphenol conjugate. Those potential grafting methods are alkaline associated, free-radical mediated, enzyme catalyzed, and chemical coupling methods. Several factors such as reaction conditions, type of proteins, and PPNs also influenced the conjugation efficiency. Various technologies, e.g., mass spectroscopy, fluorescence spectroscopy, UV spectroscopy, Fourier transform infrared spectroscopy, circular dichroism, and sodium dodecyl sulfate polyacrylamide gel electrophoresis have been used to elucidate conjugation and structural alternation of proteins and some properties of resulting conjugates. The prepared protein-PPN conjugates have been documented to enhance the bioactivities and functional properties of an initial protein. Moreover, conjugates have been employed in emulsions or as nanoparticles for nutraceutical delivery. Edible-films for food packaging and hydrogels for controlled drug release have been developed using protein-PPN conjugates. This chapter focuses on the methodologies and characteristics of protein-PPN conjugates and their applications in various food systems and nutraceutical field.

Antioxidant activities of chlorogenic acid derivatives with different acyl donor chain lengths and their stabilities during in vitro simulated gastrointestinal digestion

In this study, chlorogenic acid (CA) was acylated with vinyl esters of different carbon chain lengths under the action of the lipase Lipozyme RM. Five CA derivatives (C2-CA, C4-CA, C6-CA, C8-CA, and C12-CA) with different lipophilicities were obtained, and their digestive stabilities and antioxidant activities were evaluated. The lipophilicities were positively correlated with the digestive stabilities of CA derivatives. The antioxidant activities of CA derivatives did not change with the reduction of phenolic hydroxyl groups, and their capacity to scavenge 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS+•) and 1,1-diphenyl-2-picrylhydrazyl (DPPH•) were similar to those of CA. In cellular antioxidant activity (CAA) tests, it was found that the capacity of these derivates to cross cell membranes were enhanced upon enhancing lipophilicity, and their antioxidant activities were improved. C12-CA showed the best antioxidant activity with a median effective dose (EC50) of 9.40 μg/mL, which was significantly lower than that of CA (i.e., 29.08 μg/mL).