Synthesis, characterization, bioactivity and potential application of phenolic acid grafted chitosan: A review

Highlights

• This review concerns on phenolic acid grafted chitosan (phenolic acid-g-chitosan).

• Chemical, enzymatic and electrochemical methods can be used for conjugate synthesis.

• Phenolic acid-g-chitosan can be characterized by several instrumental methods.

• Phenolic acid-g-chitosan has ideal physicochemical property and biological activity.

• Phenolic acid-g-chitosan has wide applications in food technology.

Abstract

In recent years, increasing attention has been paid to the grafting of phenolic acid onto chitosan in order to enhance the bioactivity and widen the application of chitosan. Here, we present a comprehensive overview on the recent advances of phenolic acid grafted chitosan (phenolic acid-g-chitosan) in many aspects, including the synthetic method, structural characterization, biological activity, physicochemical property and potential application. In general, four kinds of techniques including carbodiimide based coupling, enzyme catalyzed grafting, free radical mediated grafting and electrochemical methods are frequently used for the synthesis of phenolic acid-g-chitosan. The structural characterization of phenolic acid-g-chitosan can be determined by several instrumental methods. The physicochemical properties of chitosan are greatly altered after grafting. As compared with chitosan, phenolic acid-g-chitosan exhibits enhanced antioxidant, antimicrobial, antitumor, anti-allergic, anti-inflammatory, anti-diabetic and acetylcholinesterase inhibitory activities. Notably, phenolic acid-g-chitosan shows potential applications in many fields as coating agent, packing material, encapsulation agent and bioadsorbent.

Introduction

Chitin is the second most abundant polysaccharide mainly extracted from the exoskeleton of sea creatures, such as crayfish, lobster, prawns, crab and shrimp. Chitosan is the deacetylated product of chitin obtained by alkaline treatment (Kumar, Muzzarelli, Muzzarelli, Sashiwa, & Domb, 2004). Chitosan is also a unique cationic polysaccharide with many special features including viscosity, polyelectrolyte behavior, mucoadhesivity, film forming and metal chelating ability (Pillai, Paul, & Sharma, 2009; Shukla, Mishra, Arotiba, & Mamba, 2013). Besides, due to its non-toxic, non-antigenic, biocompatible and biodegradable properties, chitosan has wide applications in food, tissue engineering, pharmaceutical, textile, agriculture, water treatment and cosmetics industries (Aider, 2010; Ngo et al., 2015; Rinaudo, 2006; Suh & Matthew, 2000; Vakili et al., 2014). However, the use of chitosan is greatly limited by its poor solubility in water, because chitosan is only soluble in acidic media. Chemical modification is an efficient approach to improve the water solubility as well as endow some new characteristics for chitosan (Alves & Mano, 2008; Prashanth & Tharanathan, 2007). Among various chemical modification methods, graft copolymerization reaction has been most widely used (Jayakumar, Prabaharan, Reis, & Mano, 2005; Thakur & Thakur, 2014). Graft copolymerization can introduce desired physicochemical and biological properties into chitosan, making molecular design possible.

In order to improve the physicochemical and biological properties of chitosan, increasing efforts have been made to graft phenolics, especially phenolic acids onto chitosan through graft copolymerization since 2008 (Božič, Gorgieva, & Kokol, 2012; Curcio et al., 2009; Pasanphan & Chirachanchai, 2008). Phenolics are the most abundant secondary metabolites widespread throughout the plant kingdom, such as fruit, vegetables, cereals, olives, dry legumes, cocoa, tea, coffee, and wine (Oroian & Escriche, 2015). Phenolics are an essential part of human diet with various valuable biological activities, including antioxidant, antimicrobial, anti-diabetic, anti-inflammatory, anticancer and metabolic regulation properties (Ali Asgar, 2013; Roleira et al., 2015; Shahidi & Ambigaipalan, 2015). More than 8000 naturally occurring chemical compounds belong to the category of “phenolics”, which share a common structural feature, i.e. an aromatic ring bearing at least one hydroxyl substituent (Costa et al., 2015). Based on the number of phenol rings and the way they bond, phenolics can be divided into five different categories including phenolic acids, flavonoids, tannins, stilbenes and lignans (Stalikas, 2007). As an important category of phenolics, naturally occurring phenolic acids usually possess one carboxylic acid group with two distinctive carbon frameworks, i.e. the hydroxybenzoic and hydroxycinnamic structures (Khadem & Marles, 2010; Lochab, Shukla, & Varma, 2014). Accordingly, phenolic acids can be further divided into two subcategories: hydroxybenzoic acids and hydroxycinnamic acids (Table 1). In the past decade, phenolic acids have been demonstrated to possess potent antioxidant, antimicrobial, anticancer, antiviral, anti-inflammatory, antimutagenic, antirheumatic, antipyretic, antiseptic, anthelmintic, neuroprotective and hepatoprotective activities (Heleno, Martins, Queiroz, & Ferreira, 2015).

Nowadays, four kinds of grafting techniques including carbodiimide based coupling, enzyme catalyzed grafting, free radical mediated grafting and electrochemical methods are frequently used for the synthesis of phenolic acid grafted chitosan (phenolic acid-g-chitosan) (Božič, Štrancar, & Kokol, 2013; Kim et al., 2010; Liu, Lu, Kan, & Jin, 2013b; Pasanphan & Chirachanchai, 2008). The introduction of phenolic groups onto chitosan backbone not only greatly alters the structural and physicochemical properties (solubility, thermal stability, crystallinity and rheological properties) of chitosan, but also remarkably increases biological activities (antioxidant, antimicrobial, antitumor, anti-allergic, anti-inflammatory, anti-diabetic and acetylcholinesterase inhibitory activity) of chitosan (Cirillo et al., 2016; Liu, Lu, Kan, Wen, & Jin, 2014a; Oliver, Vittorio, Cirillo, & Boyer, 2016). Notably, phenolic acid-g-chitosan shows potential applications in many fields of food technology, which can be used as functional foods, food coating agents, food packing materials, encapsulation agents for functional dietary ingredients, and bioadsorbents for the treatment of iron overload diseases (Aljawish, Chevalot, Jasniewski, Scher, & Muniglia, 2015; Hu et al., 2015, Liu et al., 2015b, Liu et al., 2016a). Therefore, the functional phenolic acid-g-chitosan needs to be extensively researched and utilized in the future. This review systematically focuses on the recent advances of phenolic acid-g-chitosan in many aspects, including the synthetic method, structural characterization, physicochemical property, biological activity with detailed functional mechanism, potential applications in food technology and future perspectives.