Protocatechuic acid and gallic acid improve the emulsion and thermal stability of whey protein by covalent binding

Gallic acid enhanced fiber formation in soy protein isolate-based meat analogues

This study explored the potential of gallic acid to enhance fiber formation in soy protein isolate (SPI)-based meat analogues produced from high-moisture extrusion. Specifically, the effect of gallic acid on the structure and characteristics of meat analogues was investigated. It was found that gallic acid enhanced the anisotropy index of meat analogues, with the strongest effect observed at a concentration of 0.06 mol/kg SPI. The hardness, chewiness and water binding ability of SPI-based meat analogues were also increased. Moreover, gallic acid increased the energy input to SPI during extrusion and the flow velocity difference of the SPI melt during cooling. SDS-PAGE analysis and the decrease in contents of free sulfhydryl and amino groups indicated that gallic acid induced covalent cross-linking of SPI molecules during extrusion. Also, 0.06 mol gallic acid/kg SPI had the most profound effect. Thus, it was inferred that these alterations induced promotion of fiber formation.

Enzymatic cross-linking mechanism of different structural polyphenols with Inca peanut albumin and its potential application in emulsion

In this study, four polyphenols (protocatechuic acid [PCA], vanillic acid [VA], gallic acid [GA], and syringic acid [SA]) with different types and numbers of substituents were selected for cross-linking with Inca peanut albumin (IPA) to investigate the effect of polyphenol structure on the enzyme-promoted cross-linking ability. The results showed that the enzymatic cross-linking reaction was based on the formation of quinone and hydrogen bond, and the catalytic oxidation efficiencies by laccase(L) were L-GA > L-SA > L-PCA > L-VA, with GA having the highest binding energy of -4.51 kcal/mol. Covalent binding of all four polyphenols to IPA resulted in increased surface hydrophobicity and emulsification capacity. Among them, the IPA-GA conjugates had a better stabilization ability for high oil phase emulsions. The results demonstrated that the polyhydroxy-substituted GA had a better modification effect on IPA. Therefore, the conjugates formed between polyphenols with a greater number of hydroxyl substituents (such as GA) and IPA under laccase catalysis have great potential as emulsifiers to stabilize high oil phase emulsions.

Ultrasound-induced food protein-stabilized emulsions: Exploring the governing principles from the protein structural perspective

Consumers' growing demand for healthy and natural foods has led to a preference for products with fewer additives. However, the low emulsifying properties of natural proteins often necessitate the addition of emulsifiers in food formulations. Consequently, enhancing the emulsifying properties of proteins through various modification methods is crucial to meet modern consumer demands for natural food products. High-intensity ultrasound offers a green, efficient processing technology that significantly improves the emulsifying properties of proteins. This study explores how ultrasound treatment enhances the stability of protein-based emulsions by modifying protein structures. While ultrasonic treatment does not significantly affect the primary structure of proteins, it influences the secondary, tertiary, and quaternary structures depending on the type of protein, ultrasound parameters (type, intensity, and time), and treatment conditions. The results suggest that ultrasound treatment reduces α-helix content, decreases protein particle size, and increases β-sheet content, surface hydrophobicity, free sulfhydryl groups, and zeta potential, leading to a more stable protein-based emulsion. The reduced particle size and increased flexibility of proteins induced by ultrasound enable more rapid protein adsorption at the oil-water interface, resulting in smaller emulsion droplets. This contributes to the emulsion's improved stability during storage. Future research should focus on the large-scale application of ultrasonic treatment for protein modification to produce high-quality, natural foods that meet the evolving needs of consumers.

Antigenicity elimination of ovalbumin by cold plasma-induced covalent binding with Gallic acid

The effect of cold plasma (CP) treatment in promoting the covalent grafting of ovalbumin (OVA) with gallic acid (GA) were investigated, along with identifying the binding sites in the OVA-GA complex and exploring its potential for reducing the antigenicity of OVA. The results showed that the GA content of 22.97 ± 1.27 mg/g in OVA-GA complex was obtained following 60 s of CP treatment. Using LC-MS/MS, four regions (T52-R59, V201-K207, I279-R285, and V281-K291) were identified, containing 12 GA binding sites in the OVA-GA complex. Additionally, a significant reduction in IgE binding capacity (70.83 ± 0.90 %) was observed, as confirmed by ELISA analysis. The masking/steric-hindrance effect on linear epitopes and the disruption of conformational epitopes of OVA as a result of GA grafting may be the key factors leading to the reduction in OVA antigenicity. This study highlights that promoting the grafting of polyphenols onto proteins using CP treatment is an effective strategy for reducing the antigenicity of protein allergens.

Covalent interaction of ovalbumin with proanthocyanidins improves its thermal stability and antioxidant and emulsifying activity

BACKGROUND

The structure of proanthocyanidins (PC) contains a large number of active phenolic hydroxyl groups, which makes it have strong antioxidant capacity. This study investigated the structural and functional properties of ovalbumin (OVA) modified by its interaction with PC.

RESULTS

It was found that on increasing the concentration ratio of PC to OVA from 10:1 to 40:1, the free amino and total sulfhydryl contents of OVA decreased from 470.59 ± 38.77 and 29.81 ± 0.31 nmol mg-1 to 96.61 ± 4.55 and 21.22 ± 0.78 nmol mg-1, respectively, and the free sulfhydryl content increased from 7.65 ± 0.41 to 9.48 ± 0.58 nmol mg-1. These results indicated that CN and CS bonds were formed and PC was covalently linked with OVA. The PC content in the OVA-PC conjugates increased from 281.93 ± 12.92 to 828.81 ± 46.09 nmol mg-1 on increasing the concentration ratio of PC to OVA from 10:1 to 40:1. The contents of α-helix and β-turn of OVA decreased, and the contents of β-sheet and random coil increased, confirmed by circular dichroism. The tertiary structure of OVA was also altered according to the results of fluorescence and ultraviolet absorption spectra. The surface hydrophobicity of OVA-PC conjugates decreased with increasing bound polyphenol content. The conjugation of OVA to PC significantly improved its emulsification and antioxidant activity and denaturation temperature.

CONCLUSION

This study may provide valuable information for improving OVA's functional properties and its PC conjugates for applications in the food industry. © 2024 Society of Chemical Industry.

Hydrodynamic cavitation induced fabrication of soy protein isolate-polyphenol complexes: Structural and functional properties

The combination of polyphenols and protein can improve the functional characteristics of protein. How to effectively promote the binding of polyphenols to protein is still a difficult topic. In this study, hydrodynamic cavitation (HC) was used to induce the fabrication of complexes between soy protein isolate (SPI) and different polyphenols (tannic acid (TA), chlorogenic acid (CGA), ferulic acid (FA), caffeic acid (CA), and gallic acid (GA)). The effect of HC on the interaction between polyphenols and SPI was investigated, and the structural and functional properties of the formed complexes were characterized. The results showed that HC treatment led to SPI structure stretching, which increased the binding level of polyphenols, especially that of TA (increased from 35.08 ± 0.73% to 66.42 ± 1.35%). The increase in ultraviolet-visible absorption intensity and quenching of fluorescence intensity confirmed that HC enhanced the interaction between polyphenols and protein. HC treatment reduced the contents of free sulfhydryl and amino groups in SPI-polyphenol complexes and altered their Fourier transform infrared spectroscopy, indicating that HC treatment promoted the formation of C-N and C-S bonds between SPI and polyphenols. Circular dichroism spectroscopy indicated that HC treatment altered the secondary structure of SPI-polyphenol complexes, inducing an increase in α-helix and random coil contents and a decrease in β-sheet content. Regarding functional properties, HC treatment improved the emulsification and antioxidant activity of SPI-polyphenol complexes. Therefore, HC is an effective technique for promoting the binding of polyphenols to protein.

Mechanism study on the improvement of egg white emulsifying characteristic by ultrasound synergized citral: Physicochemical properties, molecular flexibility, protein structure

As a natural emulsifier, egg white protein (EWP) has great interfacial characteristics and high security, and has broad development prospects. This study explored the impact of ultrasound synergized citral (CI) treatment on the microstructure, molecular flexibility and emulsifying property of EWP, and predicted the interaction between CI and ovalbumin (the main protein in EWP) through molecular docking. The decrease in free amino content and the growth in molecular weight of EWP suggested that CI and proteins were successfully grafted. The results of physicochemical properties revealed that UCEWP (ultrasound synergized citral-treated EWP) had smaller particle size and larger ζ-potential absolute value, which meant that the stability of UCEWP system was enhanced. From the perspective of interfacial characteristics, UCEWP had lower interfacial tension, which remarkably improved its emulsifying property. The emulsifying activity index (EAI) and emulsifying stability index (ESI) of UCEWP were 1.99 times and 3.19 times higher than that of natural EWP (NEWP). Analysis of Fourier transform infrared spectroscopy (FT-IR) and fluorescence spectroscopy illustrated that the secondary and tertiary structures of UCEWP were more disordered and stretched than those of EWPs. Protein microstructure demonstrated that UCEWP presented loose small particle distribution, and correlation analysis reflected that the improvement of molecular flexibility was positively correlated with the enhancement of emulsifying property. These results elucidated that ultrasound synergized CI treatment is an effective mean to improve the molecular flexibility and emulsifying property of EWP, which provides a valuable reference for further application of EWP.

Unveiling the transformative influence of sonochemistry on formation of whey protein isolate and green tea extract (WPI-GTE) conjugates

This study investigated the formation of conjugates between whey protein isolate (WPI) and green tea extract (GTE) using three methods: redox-pair (R), ultrasound-assisted redox-pair (RU), and ultrasonication (UL). Ultrasonication significantly reduced the reaction time for synthesizing WPI-GTE conjugates compared to the standard R method (p < 0.05). The UL methods had the highest conjugate yield determined by polyphenol binding (p < 0.05). Fourier-transform infrared spectroscopy (FTIR) and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) confirmed the conjugate formation, indicating an increased molecular weight due to protein binding with polyphenols through covalent and non-covalent bonds. Conjugates produced via ultrasonication exhibited enhanced solubility, smaller particle size, better emulsifying capacity, and improved foaming ability compared to those formed using the traditional R method (p < 0.05). However, conjugates from the R method showed higher antioxidant activity, as evidenced by DPPH•and ABTS•+ scavenging activities (p < 0.05). In conclusion, WPI-GTE conjugates created through ultrasonic treatment demonstrate potential as dual-functional ingredients, serving as both antioxidant and emulsifier.

Covalent polyphenols-proteins interactions in food processing: formation mechanisms, quantification methods, bioactive effects, and applications

Proteins and polyphenols are abundant in the daily diet of humans and their interactions influence, among other things, the texture, flavor, and bioaccessibility of food. There are two types of interactions between them: non-covalent interactions and covalent interactions, the latter being irreversible and more powerful. In this review, we systematically summarized advances in the investigation of possible mechanism underlying covalent polyphenols-proteins interaction in food processing, effect of different processing methods on covalent interaction, methods for characterizing covalent complexes, and impacts of covalent interactions on protein structure, function and nutritional value, as well as potential bioavailability of polyphenols. In terms of health promotion of the prepared covalent complexes, health effects such as antioxidant, hypoglycemic, regulation of intestinal microbiota and regulation of allergic reactions have been summarized. Also, the possible applications in food industry, especially as foaming agents, emulsifiers and nanomaterials have also been discussed. In order to offer directions for novel research on their interactions in food systems, nutritional value, and health properties in vivo, we considered the present challenges and future perspectives of the topic.

Enhancement of phycocyanin productivity and thermostability from Arthrospira platensis using organic acids

Intracellular hyperaccumulation of phycocyanin (PC) and its high susceptibility to degradation at higher temperatures are major challenging problems associated with its production from cyanobacteria. The present study evaluated different concentrations of organic acids (1, 2, and 3 mM) (citric acid, acetic acid, succinic acid, fumaric acid, and oxalic acid) under fed-batch mode on the biomass and phycobiliproteins' production from Arthrospira platensis. Besides they were evaluated at 2.5-7.5 mM as preservative to stabilize PC at high temperatures. The incorporation of 3 mM of succinic acid into the cultivation medium enhanced the biomass and PC productivity to 164.05 and 26.70 mg L-1 day-1, which was ~ 2- and threefold higher than control, respectively. The produced PC in this treatment was food-grade with a 2.2 purity ratio. The use of organic acids also enhanced the thermal stability of PC. Citric acid (7.5 mM) markedly promoted the half-life values of PC to 189.44 min compared to 71.84 min in the control. The thermodynamic analysis confirmed higher thermostability of PC in the presence of organic acids and indicated the endothermic and non-spontaneity of the thermal denaturation process. The findings of the present study confirmed that organic acids could be utilized as cost effective and sustainable compounds for promoting not only phycobiliproteins' production but also the thermostability of PC for potential application in food industry.

Molecular Mechanisms and Applications of Polyphenol-Protein Complexes with Antioxidant Properties: A Review

Proteins have been extensively studied for their outstanding functional properties, while polyphenols have been shown to possess biological activities such as antioxidant properties. There is increasing clarity about the enhanced functional properties as well as the potential application prospects for the polyphenol-protein complexes with antioxidant properties. It is both a means of protein modification to provide enhanced antioxidant capacity and a way to deliver or protect polyphenols from degradation. This review shows that polyphenol-protein complexes could be formed via non-covalent or covalent interactions. The methods to assess the complex's antioxidant capacity, including scavenging free radicals and preventing lipid peroxidation, are summarized. The combination mode, the type of protein or polyphenol, and the external conditions will be the factors affecting the antioxidant properties of the complexes. There are several food systems that can benefit from the enhanced antioxidant properties of polyphenol-protein complexes, including emulsions, gels, packaging films, and bioactive substance delivery systems. Further validation of the cellular and in vivo safety of the complexes and further expansion of the types and sources of proteins and polyphenols for forming complexes are urgently needed to be addressed. The review will provide effective information for expanding applications of proteins and polyphenols in the food industry.