Horseradish peroxidase catalyzed grafting of chitosan oligosaccharide with different flavonols: structures, antioxidant activity and edible coating application

BACKGROUND

Enzymatic catalyzed grafting of oligosaccharides with polyphenols is a safe and environmentally friendly approach to simultaneously enhance the bioactivity of oligosaccharides and the solubility of polyphenols. In this study, chitosan oligosaccharide (COS) was grafted with three different flavonols including myricetin (MYR), quercetin (QUE) and kaempferol (KAE) by horseradish peroxidase (HRP) catalysis. The structures, antioxidant activity and edible coating application of COS-flavonol conjugates were investigated.

RESULTS

The total phenol content of COS-MYR, COS-QUE and COS-KAE conjugates was 59.89, 68.37 and 53.77 mg gallic acid equivalents g^-1 , respectively. Thin layer chromatography showed the conjugates did not contain ungrafted flavonols. COS-flavonol conjugates showed ultraviolet absorption peak at about 294 nm, corresponding to the A-ring of flavonols. Fourier-transform infrared spectra of conjugates confirmed the formation of Schiff-base and Michael-addition products. The proton-nuclear magnetic resonance spectrum of COS-KAE conjugate exhibited phenyl proton signals of KAE. X-ray diffraction patterns of conjugates showed some diffraction peaks of flavonols. COS-flavonol conjugates presented rough and porous morphologies with sheet-like and/or blocky structures. The conjugates showed higher water solubility, free radical scavenging activity and reducing power than flavonols. Moreover, fish gelatin/COS-flavonol conjugate coatings effectively prolonged the shelf life of refrigerated largemouth bass (Micropterus salmoides) fillets from 5 days to 7-8 days.

CONCLUSION

COS-flavonol conjugates prepared by HRP catalysis have great potentials as novel antioxidant agents. © 2022 Society of Chemical Industry.

Molecular modifications, biological activities, and applications of chitosan and derivatives: A recent update

Polysaccharides arouse great interest due to their structure and unique properties, such as biocompatibility, biodegradability, and absence of toxicity. Polysaccharides from marine sources are particularly useful due to the wide variety of applications and biological activities. Chitosan, a deacetylated derivative of chitin, is an example of an interesting bioactive marine-derived polysaccharide. Moreover, a wide variety of chemical modifications and conjugation of chitosan with other bioactive molecules are responsible for improvements in physicochemical properties and biological activities, expanding the range of applications. An overview of the synthetic approaches for preparing chitosan, chitosan derivatives, and conjugates is described and discussed. A recent update of the biological activities and applications in different research fields, mainly focused on the last 5 years, is presented, highlighting current trends.

Physicochemical, Mechanical, and Structural Properties of Bio-Active Films Based on Biological-Chemical Chitosan, a Novel Ramon (Brosimum alicastrum) Starch, and Quercetin

The properties of biological-chemical chitosan (BCh) films from marine-industrial waste and a non-conventional Ramon starch (RS) (Brosimum alicastrum) were investigated. Blended films of BCh/RS were prepared to a volume ratio of 4:1 and 1:4, named (BChRS-80+q, biological-chemical chitosan 80% v/v and Ramon starch, BChRS-20+q, biological-chemical chitosan 20% v/v and Ramon starch, both with quercetin), Films from commercial chitosan (CCh) and corn starch (CS), alone or blended (CChCS-80+q, commercial chitosan 80% v/v and corn starch, CChCS-20+q commercial chitosan 20% v/v and corn starch, both with quercetin) were also prepared for comparison purposes. Films were investigated for their physicochemical characteristics such as thickness, moisture, swelling, water-vapor permeability, and water solubility. In addition, their mechanical and structural properties were studied using Fourier Transform Infrared Spectroscopy (FTIR), Thermogravimetric analysis (TGA) and Scanning Electron Microscopy (SEM) techniques. Antioxidant activity was evaluated as radical scavenging, and antimicrobial effect was also determined. The BCh and RS films presented similar tensile strength values compared with commercial biopolymers. Only films with chitosan presented antioxidant and antimicrobial activity. The FTIR spectra confirmed the interactions between functional groups of the biopolymers. Although, BChRS-80+q and BChRS-20+q films exhibited poor mechanical performance compared to their commercial counterparts, they showed good thermal stability, and improved antioxidant and antimicrobial activity in the presence of quercetin. BChRS-80+q and BChRS-20+q films have promising applications due to their biological activity and mechanical properties, based on a novel material that has been underutilized (Ramon starch) that does not compete with materials for human feeding and may be used as a coating for food products.

A review on chitosan and chitosan-based bionanocomposites: Promising material for combatting global issues and its applications

Over the last few years, several attempts have been made to replace petrochemical products with renewable and biodegradable components. The most challenging part of this approach is to obtain bio-based materials with properties and functions equivalent to those of synthetic products. Various naturally occurring polymers such as starch, collagen, alginate, cellulose, and chitin represent attractive candidates as they could reduce dependence on synthetic products and consequently positively impact the environment. Chitosan is also a unique bio-based polymer with excellent intrinsic properties. It is known for its anti-bacterial and film-forming properties, has high mechanical strength and good thermal stability. Nanotechnology has also applied chitosan-based materials in its most recent achievements. Therefore, numerous chitosan-based bionanocomposites with improved physical and chemical characteristics have been developed in an eco-friendly and cost-effective approach. This review discusses various sources of chitosan, its properties and methods of modification. Also, this work focuses on diverse preparation techniques of chitosan-based bionanocomposites and their emerging application in various sectors. Additionally, this review sheds light on future research scope with some drawbacks and challenges to motivate the researchers for future outstanding research works.

Chitosan derivatives-based films as pH-sensitive drug delivery systems with enhanced antioxidant and antibacterial properties

The purpose of this study was to develop and characterize chitosan (Ch)-based films incorporated with varying molecular weight (Mw) and acetylation degree (AD) chitosan-depolymerization-products (CDP), to be applied as drug delivery materials. As compared to Ch-film, optical and antioxidant potentials of Ch/CDP-based films were improved, particularly using low Mw and AD-CDP. Whereas, films water resistance, mechanical and antibacterial properties increased as CDP-Mw increased and AD decreased. For the thermal and swelling behaviors, better values were obtained using higher Mw and AD-CDP. Further, to assess their in vitro ciprofloxacin (CFX)-release behavior, loaded-CFX Ch/CDP-based films, crosslinked using glutaraldehyde, were prepared. Expect of elongation at break, crosslinked CFX-loaded films showed increased optical, water resistance, tensile strength and thermal properties, as compared to unloaded films. The CFX-release profiles indicated that a slower and sustained release was observed, particularly when using lower Mw and AD-CDP, and mainly for the crosslinked films during 48 h. These films can release CFX for up to 54% in 6 and 24 h, at pH 1.2 and 7.4, respectively. Through this study, novel biodegradable, swellable and pH-sensitive crosslinked Ch/CDP-based films may be considered as suitable and promising drug delivery systems.

Trends in Chitosan as a Primary Biopolymer for Functional Films and Coatings Manufacture for Food and Natural Products

Some of the current challenges faced by the food industry deal with the natural ripening process and the short shelf-life of fresh and minimally processed products. The loss of vitamins and minerals, lipid oxidation, enzymatic browning, and growth of microorganisms have been the main issues for many years within the innovation and improvement of food packaging, which seeks to preserve and protect the product until its consumption. Most of the conventional packaging are petroleum-derived plastics, which after product consumption becomes a major concern due to environmental damage provoked by their difficult degradation. In this sense, many researchers have shown interest in edible films and coatings, which represent an environmentally friendly alternative for food packaging. To date, chitosan (CS) is among the most common materials in the formulation of these biodegradable packaging together with polysaccharides, proteins, and lipids. The good film-forming and biological properties (i.e., antimicrobial, antifungal, and antiviral) of CS have fostered its usage in food packaging. Therefore, the goal of this paper is to collect and discuss the latest development works (over the last five years) aimed at using CS in the manufacture of edible films and coatings for food preservation. Particular attention has been devoted to relevant findings in the field, together with the novel preparation protocols of such biodegradable packaging. Finally, recent trends in new concepts of composite films and coatings are also addressed.

Antioxidant Activity of Synthetic Polymers of Phenolic Compounds

In recent years, developing potent antioxidants has been a very active area of research. In this context, phenolic compounds have been evaluated for their antioxidant activity. However, the use of phenolic compounds has also been limited by poor antioxidant activity in several in vivo studies. Polymeric phenols have received much attention owing to their potent antioxidant properties and increased stability in aqueous systems. To be truly effective in biological applications, it is important that these polymers be synthesized using benign methods. In this context, enzyme catalyzed synthesis of polymeric phenols has been explored as an environmentally friendly and safer approach. This review summarizes work in enzymatic syntheses of polymers of phenols. Several assays have been developed to determine the antioxidant potency of these polymeric phenols. These assays are discussed in detail along with structure-property relationships. A deeper understanding of factors affecting antioxidant activity would provide an opportunity for the design of versatile, high performing polymers with enhanced antioxidant activity.

Perspectives on “Game Changer” Global Challenges for Sustainable 21st Century: Plant-Based Diet, Unavoidable Food Waste Biorefining, and Circular Economy

Planet Earth is under severe stress from several inter-linked factors mainly associated with rising global population, linear resource consumption, security of resources, unsurmountable waste generation, and social inequality, which unabated will lead to an unsustainable 21st Century. The traditional way products are designed promotes a linear economy that discards recoverable resources and creates negative environmental and social impacts. Here, we suggest multi-disciplinary approaches encompassing chemistry, process engineering and sustainability science, and sustainable solutions in “game changer” challenges in three intersecting arenas of food: Sustainable diet, valorisation of unavoidable food supply chain wastes, and circularity of food value chain systems aligning with the United Nations’ seventeen Sustainable Development Goals. In the arena of sustainable diet, comprehensive life cycle assessment using the global life cycle inventory datasets and recommended daily servings is conducted to rank food choices, covering all food groups from fresh fruits/vegetables, lentils/pulses and grains to livestock, with regard to health and the environment, to emphasise the essence of plant-based diet, especially plant-based sources of protein, for holistic systemic sustainability and stability of the earth system. In the arena of unavoidable food supply chain wastes, economically feasible and synergistically (energy and material) integrated innovative biorefinery systems are suggested to transform unavoidable food waste into functional and platform chemical productions alongside energy vectors: Fuel or combined heat and power generation. In the arena of circularity of food value chain systems, novel materials and methods for plant-based protein functionalisation for food/nutraceutical applications are investigated using regenerative bio-surfactants from unavoidable food waste. This circular economy or industrial symbiosis example thus combines the other two arenas, i.e., plant-based protein sourcing and unavoidable food waste valorisation. The multi-disciplinary analysis here will eventually impact on policies for dietary change, but also contribute knowledge needed by industry and policy makers and raise awareness amongst the population at large for making a better approach to the circular economy of food.

Quercetin-grafted chitosan prepared by free radical grafting: characterization and evaluation of antioxidant and antibacterial properties

Chitosan (CS) is considered a versatile biopolymer with promising applications. However, it is not a good chain-breaking antioxidant due to the lack of H-atom donors. In this work, CS was combined with quercetin (Q), a natural antioxidant, via a free radical-mediated procedure to strengthen the antioxidant capacity. The successful formation of Q-grafted CS (Q-CS) was confirmed by ultraviolet-visible absorbance and Fourier transform infrared spectroscopy. After combination, the obtained Q-CS had a phenolic content of 13.9 mg QE/g Q-CS and showed a lower crystallinity and thermal stability than the native CS. The 2,2-diphenyl-1-picrylhydrazyl, 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid), superoxide, and hydroxyl radical scavenging activities of Q-CS were higher than those of CS, illustrating that grafting with Q is an available way to improve the antioxidant capacity of CS. In addition, Q-CS showed higher minimal inhibitory concentrations against tested bacteria than CS, suggesting that combining with Q has a negative effect on the antibacterial activity of CS. Our results indicate that Q-CS may have great potential for applications in the fields of food and healthcare.

Natural antidotes and management of metal toxicity

The global burden of heavy metal especially mercury, arsenic, lead, and cadmium toxicities remains a significant public health challenge. Developing nations are particularly at high risk and carry the highest burden of this hazard. Chelation therapy has been the mainstay for treatment of heavy metal poisoning where the chelating agent binds metal ions to form complex ring-like structures called "chelates" to enhance their elimination from the body. Metal chelators have some drawbacks such as redistribution of some heavy metals from other tissues to the brain thereby increasing its neurotoxicity, causing loss of essential metals such as copper and zinc as well as some serious adverse effects, e.g., hepatotoxicity. The use of natural antidotes, which are easily available, affordable, and with little or no side effects compared to the classic metal chelators, is the focus of this review and suggested as cheaper options for developing nations in the treatment of heavy metal poisoning.

Cross-Linking Chitosan into Hydroxypropylmethylcellulose for the Preparation of Neem Oil Coating for Postharvest Storage of Pitaya (Stenocereus pruinosus)

The market trend for pitaya is increasing, although the preservation of the quality of this fruit after the harvest is challenging due to microbial decay, dehydration, and oxidation. In this work, the application of antimicrobial chitosan-based coatings achieved successful postharvest preservation of pitaya (Stenocereus pruinosus) during storage at 10 ± 2 °C with a relative humidity of 80 ± 5%. The solution of cross-linked chitosan with hydroxypropylmethylcellulose with entrapped Neem oil (16 g·L^-1) displayed the best postharvest fruit characteristics. The reduction of physiological weight loss and fungal contamination, with an increased redness index and release of azadirachtin from the microencapsulated oil, resulted in up to a 15 day shelf life for this fruit. This postharvest procedure has the potential to increase commercial exploitation of fresh pitaya, owing to its good taste and high content of antioxidants.

Recent advances in flavonoid-grafted polysaccharides: Synthesis, structural characterization, bioactivities and potential applications

Plant derived flavonoids have been demonstrated to possess many valuable biological functions. In recent years, flavonoids have been successfully conjugated with polysaccharides through different graft copolymerization methods including chemical coupling, enzyme catalysis, free radical mediated grafting, and acid catalyzed condensation reactions. The successful grafting of flavonoids onto polysaccharides can be confirmed by several instrumental methods. The conjugation of flavonoids can significantly improve the antioxidant, antimicrobial, antitumor, hepatoprotective and enzyme inhibition properties of polysaccharides. Moreover, the applications of polysaccharides in food and pharmaceutical industries can be greatly broadened by grafting with flavonoids. Flavonoid-grafted polysaccharides can be developed as films for active packaging, hydrogels for controlled drug release, micelles for oral drug delivery, and emulsions for nutraceutical delivery. In general, the bioactivities and applications of conjugates are closely related to the type of flavonoid grafted, the grafting method used as well as the grafting efficiency. Recent advances in the synthesis, structural characterization, bioactivities and potential applications of flavonoid-grafted polysaccharides are summarized in this review.

Chitosan nanoparticles plus quercetin suppress the oxidative stress, modulate DNA fragmentation and gene expression in the kidney of rats fed ochratoxin A-contaminated diet

This study aimed to evaluate the protective role of chitosan nanoparticles (COS-NPs) singly or plus quercetin (Q) against OTA-induced oxidative stress and renal genotoxicity. Twelve groups of male Sprague-Dawley rats were treated orally for 3 weeks included the control group, animals fed OTA-contaminated diet (3 mg/kg diet); COS-NPs-treated groups at low (140 mg/kg b.w.) or high (280 mg/kg b.w.) dose, Q-treated group (50 mg/kg b.w.), Q plus low or high dose of COS-NPs-treated groups and OTA plus Q and/or COS-NPs at the two tested doses-treated groups. The results indicated that COS-NPs were roughly rod in shape with average particle size of 200 nm and zeta potential 31.4 ± 2.8 mV. Animals fed OTA-contaminated diet showed significant changes in serum biochemical parameters, increase kidney MDA and DNA fragmentation and decreased GPx and SOD gene expression accompanied with severe histological changes. Q and/or COS-NPs at the two tested doses induced significant improvements in all tested parameters and succeeded to overcome these effects especially in the animals treated with Q plus the high dose of COS-NPs. It could be concluded that COS-NPs are promise candidate to enhance the antioxidant effect of Q and protect against the nephrotoxicity of OTA in high endemic areas.

Characterization of a Chitosanase from Jelly Fig (Ficus awkeotsang Makino) Latex and Its Application in the Production of Water-Soluble Low Molecular Weight Chitosans

A chitosanase was purified from jelly fig latex by ammonium sulfate fractionation (50–80% saturation) and three successive column chromatography steps. The purified enzyme was almost homogeneous, as determined by SDS-polyacrylamide gel electrophoresis (SDS-PAGE) and gel activity staining. The molecular mass of the enzyme was 20.5 kDa. The isoelectric point (pI) was <3.5, as estimated by isoelectric focusing electrophoresis on PhastGel IEF 3-9. Using chitosan as the substrate, the optimal pH for the enzyme reaction was 4.5; the kinetic parameters K_m and V_max were 0.089 mg mL^-1 and 0.69 μmol min^-1 mg^-1, respectively. The enzyme showed activity toward chitosan polymers which exhibited various degrees of deacetylation (21–94%). The enzyme hydrolyzed 70–84% deacetylated chitosan polymers most effectively. Substrate specificity analysis indicated that the enzyme catalyzed the hydrolysis of chitin and chitosan polymers and their derivatives. The products of the hydrolysis of chitosan polymer derivatives, ethylene glycol (EG) chitosan, carboxymethyl (CM) chitosan and aminoethyl (AE) chitosan, were low molecular weight chitosans (LMWCs); these products were referred to as EG-LMWC, CM-LMWC and AE-LMWC, respectively. The average molecular weights of EG-LMWC, CM-LMWC and AE-LMWC were 11.2, 11.2 and 8.89 kDa, respectively. All of the LMWC products exhibited free radical scavenging activities toward ABTS^•+, superoxide and peroxyl radicals.

Chitosan nanoparticles and quercetin modulate gene expression and prevent the genotoxicity of aflatoxin B1 in rat liver

The aims of the current study were to prepare chitosan nanoparticles (CNPs) and to evaluate its protective role alone or in combination with quercetin (Q) against AFB₁-induce cytotoxicity in rats. Male Sprague-Dawley rats were divided into 12 groups and treated orally for 4 weeks as follow: the control group, the group treated with AFB₁ (80 μg/kg b.w.) in corn oil, the groups treated with low (140 mg/kg b.w.) or high (280 mg/kg b.w.) dose of CNPs, the group treated with Q (50 mg/kg b.w.), the groups treated with Q plus the low or the high dose of CNPs and the groups treated with AFB₁ plus Q and/or CNPs at the two tested doses. The results also revealed that administration of AFB₁ resulted in a significant increase in serum cytokines, Procollagen III, Nitric Oxide, lipid peroxidation and DNA fragmentation accompanied with a significant decrease in GPx I and Cu–Zn SOD-mRNA gene expression. Q and/or CNPs at the two tested doses overcome these effects especially in the group treated with the high dose of CNPs plus Q. It could be concluded that CNPs is a promise candidate as drug delivery enhances the protective effect of Q against the cytogenetic effects of AFB₁ in high endemic areas.