Duck egg albumen hydrolysate-epigallocatechin gallate conjugates: Antioxidant, emulsifying properties and their use in fish oil emulsion

Insights into the emulsifying effect and oxidation stability of myofibrillar protein-diacylglycerol emulsions containing catechin at different ionic strengths

The purpose of this study was to investigate the effects of different ionic strengths on the emulsifying and oxidation stabilities of myofibrillar protein-diacylglycerol emulsions containing catechin (MP-DAG-C), in which lard, unpurified glycerolytic lard (UGL), and purified glycerolytic lard (PGL) were used as oil phases in this study, respectively. Results revealed that emulsifying ability was significantly improved by UGL and PGL (P < 0.05). Meanwhile, the emulsifying activity and stability, absolute ξ-potential value, shear viscosity, and dynamic rheological characteristic of emulsions increased with the increase of ionic strength (P < 0.05) remarkablely, which reached the maximum value at 0.6-M sodium chloride (NaCl). The droplets of emulsions at 0.6-M ionic strength were smallest and distributed most uniformly compared to other NaCl conditions. The formation of thiobarbituric acid substances and carbonyls increased, and the total sulfydryl contents decreased as the extension of storage days (P < 0.05). However, the oxidation stability of MP-DAG-C emulsions was insignificantly decreased by ionic strengths (P > 0.05). The above results showed that MP-DAG-C emulsions could keep excellent emulsifying effects and oxidation stability under high ionic strengths. This study provides data support for the application of MP-DAG-C emulsions in emulsified meat products, which is benefit for promoting the development of high-quality emulsified meat products.

Preparation, structural characterization and properties of feruloyl oligosaccharide-rice protein hydrolysate conjugates

Rice protein hydrolysate (RPH) and feruloyl oligosaccharides (FOs) were conjugated under the catalysis of laccase and free radical, and the structure and properties of the resultant conjugates were studied. Electrophoresis analysis demonstrated that conjugation with FOs increased the molecular weight of some fractions in RPH, which confirmed the formation of both conjugates. The conjugation degree of laccase-induced conjugate and radical-induced conjugate was 60.45% and 22.70%, respectively. Laccase-catalyzed conjugation decreased the tyrosine residue content of RPH but had no significant effect on the free amino group content, which suggested that tyrosine residues were the conjugation site in the laccase-induced conjugate. However, radical-catalyzed conjugation decreased both the free amino group content and the tyrosine residue content, which indicated that both free amino groups and tyrosine residues were the conjugation site in the radical-induced conjugate. The ultraviolet, fluorescence and circular dichroism spectroscopy analysis revealed that conjugation with FOs significantly altered the secondary and tertiary structure of RPH. In addition, conjugation with FOs increased the solubility and antioxidant activity of RPH but decreased the emulsifying activity and stability. Particularly, the radical-induced conjugate had greater anti-aggregation capacity and antioxidant activity but lower emulsifying activity and stability than the laccase-induced conjugate, which might be due to that their conjugation site and degree were different.

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.

Improving the biological activity, functional properties, and emulsion stability of soybean meal hydrolysate via covalent conjugation with polyphenol

The use of by-products as functional components in food production is gaining popularity. This study investigated the structure, biological activity, interaction force, and emulsion stability of soybean meal hydrolysate (SMHs) after covalent conjugation with proanthocyanidin (PC), epigallocatechin (EGCG), gallic acid (GA), and caffeic acid (CA). SDS-PAGE confirmed the formation of SMHs-polyphenol conjugates. Structural analysis indicates unfolding and disordered-structure formation. This transformation directly influenced the antioxidant activity and emulsification of SMHs. The antioxidant and emulsifying properties of all covalent complexes were superior to SMHs, in order of SMHs-PC, SMHs-EGCG, SMHs-GA, and SMHs-CA. Among, SMHs-PC conjugates displayed the highest antioxidant activity (ABTS^•+ and DPPH radical scavenging capacities of 89.33% and 52.71%, respectively), total polyphenol content (235.10 mg/g), and emulsification activity (EAI) and stability (ESI) values (109.27 m²/g and 135.05 min, respectively). Moreover, SMHs-PC emulsion showed the smallest particle size (467.20 nm), highest viscosity (520.19 Pa.s), highest protein adsorption (94.33%), and lowest release rate of free fatty acids (FFAs) (18.61%) after digestion. These results provided valuable information for the use of modified SMHs as emulsifiers, which is a promising approach for increasing the value of soybean meal.

Recent Trends in Improving the Oxidative Stability of Oil-Based Food Products by Inhibiting Oxidation at the Interfacial Region

In recent years, new approaches have been developed to limit the oxidation of oil-based food products by inhibiting peroxidation at the interfacial region. This review article describes and discusses these particular approaches. In bulk oils, modifying the polarity of antioxidants by chemical methods (e.g., esterifying antioxidants with fatty alcohol or fatty acids) and combining antioxidants with surfactants with low hydrophilic–lipophilic balance value (e.g., lecithin and polyglycerol polyricinoleate) can be effective strategies for inhibiting peroxidation. Compared to monolayer emulsions, a thick interfacial layer in multilayer emulsions and Pickering emulsions can act as a physical barrier. Meanwhile, high viscosity of the water phase in emulsion gels tends to hinder the diffusion of pro-oxidants into the interfacial region. Furthermore, applying surface-active substances with antioxidant properties (such as proteins, peptides, polysaccharides, and complexes of protein-polysaccharide, protein-polyphenol, protein-saponin, and protein-polysaccharide-polyphenol) that adsorb at the interfacial area is another novel method for enhancing oil-in-water emulsion oxidative stability. Furthermore, localizing antioxidants at the interfacial region through lipophilization of hydrophilic antioxidants, conjugating antioxidants with surfactants, or entrapping antioxidants into Pickering particles can be considered new strategies for reducing the emulsion peroxidation.

Industrial Application of Protein Hydrolysates in Food

Protein hydrolysates, which may be produced by the protein in the middle of the process or added as an ingredient, are part of the food formula. In food, protein hydrolysates are found in many forms, which can regulate the texture and functionality of food, including emulsifying properties, foaming properties, and gelation. Therefore, the relationship between the physicochemical and structural characteristics of protein hydrolysates and their functional characteristics is of significant importance. In recent years, researchers have conducted many studies on the role of protein hydrolysates in food processing. This Review explains the relationship between the structure and function of protein hydrolysates, and their interaction with the main ingredients of food, to provide reference for their development and further research.

Effects of Pineapple Peel Ethanolic Extract on the Physicochemical and Textural Properties of Surimi Prepared from Silver Carp (Hypophthalmichthys molitrix)

The effects of ethanolic pineapple peel extract (PPE) powder at various concentrations (0–1.50%, w/w) on the gelling properties of silver carp surimi were investigated. The pineapple peel extract produced with 0–100% ethanol, revealed that 100% ethanol had the highest bioactive properties. Surimi gels with added PPE powder demonstrated improved gel strength (504.13 ± 11.78 g.cm) and breaking force (511.64 ± 11.80 g) up to 1% PPE addition; however, as PPE concentration increased beyond 1%, the gel strength decreased. Similarly, with the addition of 1% PPE powder, more hydrophobic bonds and fewer sulfhydryl groups and free amino groups were seen. However, the gels with PPE powder added showed a slight reduction in the whiteness of the surimi gels. FTIR analysis indicated that the fortification with PPE powder brought about the secondary structure of myofibrillar proteins; peaks shifted to the β-sheet region (PPE gels) from the α-helix region (control). SEM analysis indicated that the gel with 1% PPE powder had a relatively organized, finer and denser gel architecture. Overall results suggested that the addition of PPE powder up to 1% to the surimi gels enhanced the gelling properties as well as the microstructure of the surimi.

Recent progress in fish oil-based emulsions by various food-grade stabilizers: Fabrication strategy, interfacial stability mechanism and potential application

Fish oil, rich in a variety of long-chain ω-3 PUFAs, is widely used in fortified foods due to its broad-spectrum health benefits. However, its undesired characteristics include oxidation sensitivity, poor water solubility, and fishy off-flavor greatly hinder its exploitation in food field. Over the past two decades, constructing fish oil emulsions to encapsulate ω-3 PUFAs for improving their physicochemical and functional properties has undergone great progress. This review mainly focuses on understanding the fabrication strategies, stabilization mechanism, and potential applications of fish oil emulsions, including fish oil microemulsions, nanoemulsions, double emulsions, Pickering emulsions and emulsion gels. Furthermore, the role of oil-water interfacial stabilizers in the fish oil emulsions stability will be discussed with a highlight on food-grade single emulsifiers and natural complex systems for achieving this purpose. Additionally, its roles and applications in food industry and nutrition field are delineated. Finally, possible innovative food trends and applications are highlighted, such as novel fish oil-based delivery systems construction (e.g., Janus emulsions and nutraceutical co-delivery systems), exploring digestion and absorption mechanisms and enhancing functional evaluation (e.g., nutritional supplement enhancer, and novel fortified/functional foods). This review provides a reference for the application of fish oil-based emulsion systems in future precision diet intervention implementations.

Recent application of protein hydrolysates in food texture modification

The demand for clean labels has increased the importance of natural texture modifying ingredients. Proteins are unique compounds that can impart unique textural and structural changes in food. However, lack of solubility and extensive aggregability of proteins have increased the demand for enzymatically hydrolyzed proteins, to impart functional and structural modifications to food products. The review elaborates the recent application of various proteins, protein hydrolysates, and their role in texture modification. The impact of protein hydrolysates interaction with other food macromolecules, the effect of pretreatments, and dependence of various protein functionalities on textural and structural modification of food products with controlled enzymatic hydrolysis are explained in detail. Many researchers have acknowledged the positive effect of enzymatically hydrolyzed proteins on texture modification over natural protein. With enzymatic hydrolysis, various textural properties including foaming, gelling, emulsifying, water holding capacity have been effectively improved. It is evident that each protein is unique and imparts exceptional structural changes to different food products. Thus, selection of protein requires a fundamental understanding of its structure-substrate property relation. For wider applicability in the industrial sector, more studies on interactions at the molecular level, dosage, functionality changes, and sensorial attributes of protein hydrolysates in food systems are required.

Valorization of fish byproducts: Sources to end-product applications of bioactive protein hydrolysate

Fish processing industries result in an ample number of protein-rich byproducts, which have been used to produce protein hydrolysate (PH) for human consumption. Chemical, microbial, and enzymatic hydrolysis processes have been implemented for the production of fish PH (FPH) from diverse types of fish processing byproducts. FPH has been reported to possess bioactive active peptides known to exhibit various biological activities such as antioxidant, antimicrobial, angiotensin-I converting enzyme inhibition, calcium-binding ability, dipeptidyl peptidase-IV inhibition, immunomodulation, and antiproliferative activity, which are discussed comprehensively in this review. Appropriate conditions for the hydrolysis process (e.g., type and concentration of enzymes, time, and temperature) play an important role in achieving the desired level of hydrolysis, thus affecting the functional and bioactive properties and stability of FPH. This review provides an in-depth and comprehensive discussion on the sources, process parameters, purification as well as functional and bioactive properties of FPHs. The most recent research findings on the impact of production parameters, bitterness of peptide, storage, and food processing conditions on functional properties and stability of FPH were also reported. More importantly, the recent studies on biological activities of FPH and in vivo health benefits were discussed with the possible mechanism of action. Furthermore, FPH-polyphenol conjugate, encapsulation, and digestive stability of FPH were discussed in terms of their potential to be utilized as a nutraceutical ingredient. Last but not the least, various industrial applications of FPH and the fate of FPH in terms of limitations, hurdles, future research directions, and challenges have been addressed.

Conjoint application of ultrasonication and redox pair mediated free radical method enhances the functional and bioactive properties of camel whey-quercetin conjugates

Ultrasonication, redox-pair generated free radical method and their combination (Ultrasonication/redox-pair method) was used for production of camel whey-quercetin conjugates. FTIR and SDS-PAGE confirmed successful production of whey-quercetin conjugates using ultrasonication and ultrasonication/redox-pair method. FTIR suggested existence of covalent (appearance of new peak at 3399 cm-1) and non-covalent linkages (shifting of peak at 3271 cm-1, 1655 cm-1 (amide I), 1534 cm-1 and 1422 cm-1 (Amide II)) in the whey-quercetin conjugates. Moreover, SDS-PAGE of conjugates produced by ultrasonication as well redox-pair method indicated shifting of protein bands slightly towards high molecular weight due to increase in the mass of proteins due to the binding of polyphenols. All conjugates showed improved techno-functional and bioactive properties in comparison to whey proteins. Conjugates produced through ultrasonication showed smaller particle size, improved solubility, emulsifying and foaming properties while conjugates produced through ultrasonication/redox-pair method depicted superior antioxidant properties in comparison to whey. Furthermore, conjugated samples showed higher inhibition of enzymatic markers involved in diabetes and obesity with highest potential recorded in conjugates produced using ultrasonication. Therefore, ultrasonication can be successfully used individually as well as in combination with redox-pair for production of whey-quercetin conjugates with enhanced bioactive and techno-functional properties.

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.

Ultrasound-assisted extraction of protein from Bombay locusts and its impact on functional and antioxidative properties

Impact of ultrasound-assisted process (UAP) on yield, functional properties, antioxidant properties and molecular characteristics of protein extracted from Bombay locusts (BL) (Patanga succinta L.) was studied. Different conditions of UAP were implemented for different amplitudes (40-60%) and times (10-30 min) during aqueous extraction. Notably, UAP could enhance yield and protein recovery, compared with those from typical process (TP) (continuously stirred at 100 rpm at room temperature for 1 h). UAP conditions used governed the change of surface hydrophobicity and free α-amino content of BL. UAP could improve solubility of BL, especially at pH levels higher than 2. UAP had no significant (p > 0.05) detrimental effects on foaming capacity and stability of BL. Nevertheless, UAP, particularly at 50-60% amplitudes, affected the emulsion activity and stability of BL. UAP provided BL with high radical scavenging activities and good electron donating ability, especially that from 60% amplitude for 20 min (UAP-60/20). UAP-60/20 showed the impact on change of isoelectric point and molecular characteristic monitored by Fourier transform infrared (FTIR) of BL, compared to those from TP. In addition, BL was also an excellent source of both essential and nonessential amino acids. Therefore, UAP potentially enhanced BL extraction efficiency, resulting the BL with good functional and antioxidative properties.

Effects of sonication and ultrasound on properties and bioactivities of liposomes loaded with hydrolyzed collagen from defatted sea bass skin conjugated with epigallocatechin gallate

Hydrolyzed collagen (HC) from defatted sea bass skin conjugated with 3% epigallocatechin gallate (EGCG) was prepared and the resulting HC-EGCG conjugate at various levels (0.25%-2%, w/v) was loaded into liposome. The obtained liposomes were subjected to sonication (S). Liposome loaded with 1% conjugate showed the highest encapsulation efficiency (EE) (p < .05). When the ultrasound-assisted process (UAP) at different amplitudes (20% and 40%) and times (2, 5, 10, and 15 min) were implemented, the highest EE of conjugate-loaded liposome was found at 20% amplitude for 2 min (p < .05). When S-liposome and UAP-liposome were lyophilized, decreasing EE of both samples was observed (p < .05). Lyophilized UAP-liposome had higher stability than lyophilized S-liposome during storage at 25℃ for 28 days. Additionally, antioxidant activity in the gastrointestinal track model system (GIMs) and digest obtained from GIMs were higher for UAP-liposome (p < .05). Therefore, liposome can be used for the delivery of conjugate. PRACTICAL APPLICATIONS: HC from defatted sea bass skin is considered to possess several bioactivities, especially skin nourishment and bone strengthening. Nevertheless, antioxidant activity, related to the treatment of several ailments, is still low for HC. Thus, grafting of HC with polyphenol such as EGCG via free radical method can be used for the enhancement of the antioxidant activity of HC. Although the resulting conjugate has augmented activity, it is unstable during storage and in the gastrointestinal digestion system. Liposome is a promising means to stabilize the conjugate under harsh condition, especially with the aid of the UAP. Thus, liposome loaded with conjugate having the reduced size has higher antioxidant activity with increased stability, which can have a wider range of applications.

Effects of antioxidants, proteins, and their combination on emulsion oxidation

Lipid oxidation largely determines the quality of emulsion systems as well as their final products. Therefore, an increasing number of studies have focused on the control of lipid oxidation, particularly on its mechanism. In this review, we discuss the factors affecting the efficiency of antioxidants in emulsion systems, such as the free radical scavenging ability, specifically emphasizing on the interfacial behavior and the influence of surfactants on the interfacial distribution of antioxidants. To enhance the antioxidant efficiency of antioxidants in emulsion systems, we discussed whether the combination of antioxidants and proteins can improve antioxidant effects. The types, mixing applications, structures, interface behaviors, effects of surfactants on interfacial proteins, and the location of proteins are associated with the antioxidant effects of proteins in emulsion systems. Antioxidants and proteins can be combined in both covalent and non-covalent ways. The fabrication conditions, conjugation methods, interface behaviors, and characterization methods of these two combinations are also discussed. Our review provides useful information to guide better strategies for providing stability and controlling lipid oxidation in emulsions. The main challenges and future trends in controlling lipid oxidation in complex emulsion systems are also discussed.

A novel method for the rapid sensing of H2O2 using a colorimetric AuNP probe and its DFT study

Hydrogen peroxide (H₂O₂) has tremendous applications in industry, medicine and in our day-to-day lives. It is toxic to human health upon exposure at a high concentration. Therefore, a green and cost-effective sensing technique is greatly needed for the sensitive naked eye detection of peroxide. This study is mainly focused on the synthesis of Au nanoparticles (AuNPs) using an aqueous extract of Elsholtzia blanda, a flower that is widely available in the North Eastern part of India, the characterization of which was carried out using different analytical techniques. The bioactive molecule (epigallocatechin gallate) present in the aqueous extract was identified, isolated and confirmed through high-performance liquid chromatography-photodiode array, high-resolution mass spectrometry and nuclear magnetic resonance spectroscopy analysis which could be responsible for the reduction of Au³⁺ ions. By approaching this greener route, the synthesized nanomaterial was further used as a colorimetric probe for the detection of H₂O₂ and the degradation of AuNPs was observed. The limit of detection was found to be 0.7435 μM in the present work. The degradation of the AuNPs was found to be linearly dependent on peroxide concentration. Along with these results, kinetic studies were carried out by considering different effects to monitor the sensing speed of the AuNPs. The plausible mechanism of the work was supported by density functional theory study.

Conjugate between hydrolyzed collagen from defatted seabass skin and epigallocatechin gallate (EGCG): characteristics, antioxidant activity and in vitro cellular bioactivity

Conjugation between peptides and polyphenols, especially epigallocatechin gallate (EGCG) using covalent grafting, is a promising method that can modify peptides or augment their antioxidant activities. Moreover, the resulting conjugates can be intensively served as functional ingredient or supplement. Thus, the objectives of the present study were to investigate the grafting between hydrolyzed collagen (HC) from defatted seabass skin and EGCG and to study characteristics as well as bioactivities of the obtained HC-EGCG conjugate. Levels of EGCG used (1-5%, w/w) affected surface hydrophobicity (SH) and antioxidant activities of the conjugates. Overall, the addition of EGCG at 3% to HC (HC-3% EGCG) increased SH, ABTS radical scavenging and metal chelating activities (p < 0.05). FTIR spectra of HC-3% EGCG revealed the interaction between HC and EGCG via H-bonding and covalent interaction. Sephadex G-25 fraction of conjugate with molecular weight (MW) of 2771 Da rendered the highest redox ability. When HC-3% EGCG was applied in fibroblast (MRC-5) and keratinocyte (HaCaT) cells, all levels tested (125-1000 μg mL-1) had no toxicity on both cells. Higher proliferation of both cells were attained with increasing levels of HC-3% EGCG, particularly at 500 and 1000 μg mL-1 (p < 0.05). Moreover, both levels used had cytoprotective ability against reactive oxygen species (ROS) as evidenced by lowered ROS and cell death detected as compared to those found in cells induced with H2O2 or AAPH alone (p < 0.05) for both cells. HC-3% EGCG could serve as an effective antioxidant for application in foods or as supplement for skin nourishment.

Pacific white shrimp (Litopenaeus vannamei) shell chitosan and the conjugate with epigallocatechin gallate: Antioxidative and antimicrobial activities

Chitin was isolated from Pacific white shrimp (Litopenaeus vannamei) shell by demineralization and deproteinization using 1 M HCl (1:20, w/v) for 2 hr and 1 M NaOH (1:30 w/v) for 80 min at 70ºC, respectively, with 29.96% optimum yield. Thereafter, the chitin was deacetylated at various temperatures for different times, in which the chitosan prepared at 130ºC for 4 hr (CS-130-4) showed higher yield (73.11%), crystallinity index (19.75%), and 85.28% degree of deacetylation (DDA) as measured by ¹ H-NMR. CS-130-4 was then conjugated to epigallocatechin gallate (EGCG) at various concentrations (2-8%, w/w of chitosan). CS-130-4 was grafted with 8% EGCG (CE-8) had the higher conjugation efficiency (92.63%) and antimicrobial/antioxidant activities as compared to other conjugates (p < .05). ¹ H-NMR analysis also confirmed the successful conjugation of CE-8. All the conjugates were completely water soluble. Therefore, CE-8 may be used as the natural antimicrobial and antioxidant agents in various food products. PRACTICAL APPLICATIONS: Shrimp shells are generally considered as processing by-products of the shellfish industries and can cause environmental pollution when improperly disposed. Chitosan from shrimp shells has been widely produced but it is soluble mainly in acidic solutions, which limits its applications. However, grafting of epigallocatechin gallate (EGCG) onto chitosan yielded water-soluble conjugates with enhanced antioxidant and antimicrobial properties. Although several preservatives have been applied in foods, their health hazards have been a major concern. To mitigate this limitation, chitosan-EGCG conjugates could be employed as alternative natural preservatives or additives for shelf-life extension of various foods.

Analysis of the interaction between cyanidin-3-O-glucoside and casein hydrolysates and its effect on the antioxidant ability of the complexes

The interaction between cyanidin-3-O-glucoside with casein and casein hydrolysates and its effects on the antioxidant activity of complexes were investigated. Fluorescence spectroscopy results indicated that the interaction between cyanidin-3-O-glucoside and casein was primarily mediated by Van der Waals forces or hydrogen bonds and stronger than the interaction between cyanidin-3-O-glucoside and casein hydrolysates mainly via hydrophobic interaction. Circular dichroism and Fourier-transform infrared spectroscopy analysis showed the secondary structure of casein/casein hydrolysates had a slight change after binding with cyanidin-3-O-glucoside. And larger particles formed due to the protein aggregation induced by the complexation of casein/casein hydrolysates with cyanidin-3-O-glucoside. The antioxidant activity assessments revealed that the synergistic effect was observed in FRAP assay, whereas an antagonistic effect in ABTS assay between casein/casein hydrolysates and cyanidin-3-O-glucoside, which were produced due to the casein/casein hydrolysates-cyanidin-3-O-glucoside interaction. These results would be helpful in designing functional beverages containing anthocyanins and protein hydrolysates with enhanced antioxidant ability.

Nutraceutical profiling of surimi gel containing β-glucan stabilized virgin coconut oil with and without antioxidants after simulated gastro-intestinal digestion

Surimi gels containing β-glucan stabilized virgin coconut oil (VCO) were subjected to simulated gastrointestinal digestion and the resulting digest was analyzed for nutraceutical properties. β-glucan stabilized VCO nanoemulsion (βG-V-N) remarkably improved antioxidant activities of the surimi digest. When epigallocatechin gallate (EGCG) was added in nanoemulsion, the surimi digest showed the highest antioxidant activities. Antidiabetic activity of the digest was also improved by the addition of βG-V-N comprising EGCG. Nevertheless, the addition of βG-V-N lowered ACE inhibitory activity of surimi digest. The surimi digest from the gel added with βG-V-N possessed an inhibitory effect on five cancer cell lines including HEK (Human embryonic kidney 293 cells), MCF-7 (breast cancer cell line), U87 (human glioma), HeLa (human cervical cancer), and IMR-32 (human neuroblastoma), regardless of EGCG or α-tocopherol incorporated. This study demonstrated that surimi gel supplemented with βG-V-N in the presence of EGCG exhibited nutraceutical potential and could be used as a functional food.

Preparation and characterization of squid pen chitooligosaccharide–epigallocatechin gallate conjugates and their antioxidant and antimicrobial activities

Chitooligosaccharide (COS) and epigallocatechin-3-gallate (EGCG) at various concentrations were used for the preparation of COS–EGCG conjugates. The highest total phenolic content (TPC), representing the amount of EGCG conjugated, was obtained for 1 wt% COS together with EGCG at 0.5 wt% (C1-E0.5-conjugate) or 1.0 wt% (C1-E1.0-conjugate) (66.83 and 69.22 mg EGCG per g sample, respectively) (p < 0.05). The 2,2-diphenyl-1-picryl-hydrazyl-hydrate (DPPH) and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical scavenging activities (DRSA and ARSA, respectively) and ferric reducing antioxidant power (FRAP) of all the samples showed similar trends with TPC. The C1-E0.5-conjugate had higher DRSA, ARSA, FRAP and oxygen radical absorbance capacity (ORAC) values than COS (p < 0.05). Similarly, the antimicrobial activity of COS increased when conjugated with EGCG (p < 0.05). FTIR, ¹H-NMR and ¹³C-NMR analyses confirmed the successful grafting of EGCG with COS. Therefore, 1 wt% COS and 0.5 wt% EGCG were used for the production of a conjugate with augmented antioxidant activity, which could be used to retard lipid oxidation of fatty foods.

Chitooligosaccharide from squid pen showed increases in both antioxidant and antimicrobial activities via conjugation with epigallocatechin-gallate (EGCG).