Intelligent Food Packaging: Quaternary Ammonium Chitosan/Gelatin Blended Films Enriched with Blueberry Anthocyanin-Derived Cyanidin for Shrimp and Milk Freshness Monitoring.

Blueberry anthocyanin-derived cyanidin (BAC) was used to prepare a series of responsive food freshness packaging films by compounding it with quaternary chitosan (QC) and gelatin (G). The fundamental properties, pH sensitivity, and functional attributes of the films were examined. The BAC solutions exhibited notable variations in color (from red to pink to violet) under different pH conditions. The incorporation of BAC resulted in improved UV-vis shielding capabilities but compromised the mechanical strength of the films (with tensile strength values from 85.02 to 44.89 MPa, elongation at break from 13.08% to 3.6%, and water vapor transmission rates from 5.24 × 10-9 to 7.80 × 10-9 g m-1 s-1 Pa-1). The QC-G-BAC films, containing 5-15 wt% BAC, exhibited noticeable color changes in acidic/ammonia environments within a short timeframe, easily discernible to the naked eye. Furthermore, the inclusion of BAC significantly enhanced the antioxidant and antimicrobial properties of the films. The addition of 5-15 wt% BAC to QC-G-BAC films could be employed for assessing the freshness of fresh shrimp (from red to dark red) and pasteurized milk (from red to dark earthy yellow). Among them, the total color difference (ΔE) of QC-G-BAC5 film was significantly correlated with the pH, acidity, and total colony count of pasteurized milk (R = 0.846, -0.930, -0.908, respectively). This new concept in smart packaging offers a straightforward and user-friendly freshness indicator.

Preparation, characterization and application of antioxidant packaging films based on chitosan-epicatechin gallate conjugates with different substitution degrees.

In this study, chitosan (CS) was conjugated with epicatechin gallate (ECG) to prepare CS-ECG conjugates with different substitution degrees (5.18 %, 6.36 % and 7.74 %). Then, antioxidant packaging films were fabricated by blending CS and CS-ECG conjugates. The impact of CS-ECG conjugates' substitution degree on the functionality of CS/CS-ECG films was determined. CS-ECG conjugates showed UV absorption at 275 nm, proton signal at 6.85 ppm and infrared absorption at 1533 cm-1, assigning to the conjugated ECG. As compared with CS, CS-ECG conjugates exhibited less crystalline state but higher antioxidant activity. The structural characterization of CS/CS-ECG films showed CS and CS-ECG conjugates formed hydrogen bonds. CS/CS-ECG films displayed 26.35 %-29.23 % water solubility, 85.61°-86.96° water contact angle, 3.11-3.41 × 10-11 g m-1 s-1 Pa-1 water vapor permeability, 0.29-0.34 cm3 mm m-2 day-1 atm-1 oxygen permeability, 31.54-36.20 MPa tensile strength, 50.12 %-56.40 % elongation at break, as well as potent antioxidant activity and oil oxidation inhibitory ability. Notably, the film containing CS-ECG conjugate with 7.74 % substitution degree had the strongest barrier ability, mechanical property, antioxidant activity and oil oxidation inhibitory ability. Results suggested the substitution degree of CS-ECG conjugates was positively correlated with the barrier, mechanical and antioxidant properties of CS/CS-ECG films.

Recent advances on the preparation conditions, structural characteristics, physicochemical properties, functional properties and potential applications of dialdehyde starch: A review.

Starch, a natural storage polysaccharide of plant kingdom, has many industrial applications. However, native starch has some inherent shortages, which can be overcome by structural modification. Dialdehyde starch, one kind of oxidized starch produced by periodate oxidation, has good physical properties and bioactivities with wide applications in different fields. Dialdehyde starch is typically achieved by oxidizing native starch slurry through periodate oxidation under controlled reaction conditions. Several factors including the source of starch, the type of oxidant, the molar ratio of oxidant to starch, reaction temperature, reaction time and solution pH value can influence the synthesis of dialdehyde starch. Dialdehyde starch shows different spectroscopic/chromatographic characters and physicochemical properties from native starch. Moreover, dialdehyde starch exhibits good antioxidant activity, antimicrobial activity and cross-linking property. Based on these functional properties, dialdehyde starch has shown application potentials in food packaging, thermoplastic production, enzyme immobilization, heavy metal ion adsorption, drug delivery, wood adhesion and leather tanning. In this review, the preparation conditions, structural characteristics, physicochemical properties, functional properties and potential applications of dialdehyde starch are summarized for the first time. The future research and development prospects of dialdehyde starch are also discussed.

Antioxidant packaging films developed by in-situ cross-linking chitosan with dialdehyde starch-catechin conjugates.

In this study, four dialdehyde starch-catechin (DAS-catechin) conjugates were prepared by conjugating (-)-epicatechin (EC), (-)-epigallocatechin (EGC), (-)-epicatechin gallate (ECG) and (-)-epigallocatechin gallate (EGCG) with dialdehyde starch. Then, DAS-catechin conjugates were used as antioxidant and cross-linking agents to produce chitosan (CS) based antioxidant packaging films. The functionality of CS/DAS-catechin conjugate films was determined. Results showed four DAS-catechin conjugates formed Schiff-base linkages and hydrogen bond interactions with CS, resulting in improved film uniformity. Compared with plain CS film, CS/DAS-catechin conjugate films owned higher UV-vis light, water vapor and oxygen barrier ability, lower swelling degree, and stronger tensile strength, thermal stability and antioxidant activity. The cross-linking between CS and DAS-catechin conjugates delayed the biodegradable process of CS film. CS/DAS-catechin conjugate films showed good performance on inhibiting sunflower seed oil oxidation. Notably, CS/DAS-ECG conjugate film had the highest oxygen barrier, mechanical and antioxidant performances among four CS/DAS-catechin conjugate films. Therefore, CS/DAS-ECG conjugate film is an antioxidant packaging candidate for edible oil.

Improving the digestive stability and prebiotic effect of carboxymethyl chitosan by grafting with gallic acid: In vitro gastrointestinal digestion and colonic fermentation evaluation.

Carboxymethyl chitosan (CMCS) is a useful polysaccharide with potential applications in food, cosmetic and biomedical industries. Nonetheless, CMCS is unfavorable for maintaining intestinal flora balance. In this study, gallic acid (GA) was grafted with CMCS through ascorbic acid/hydrogen peroxide initiated graft copolymerization reaction, producing GA grafted CMCS (GA-g-CMCS). The digestive and fermentative behavior of CMCS and GA-g-CMCS were investigated by using in vitro simulated gastrointestinal digestion and colonic fermentation models. Results showed that the average molecular weight (Mw) of CMCS gradually decreased during saliva-gastro-intestinal digestion, changing from original sheet-like morphology to porous and rod-like fragments. However, the Mw and morphology of GA-g-CMCS were almost unchanged under saliva-gastro-intestinal digestion. Meanwhile, the grafted GA moiety was not released from GA-g-CMCS during saliva-gastro-intestinal digestion. As compared with CMCS fermentation, GA-g-CMCS fermentation significantly suppressed the relative abundance of Escherichia-Shigella, Paeniclostridium, Parabacteroides, Lachnoclostridium, Clostridium_sensu_stricto_1, UBA1819 and Butyricimonas, while facilitated the relative abundance of Enterobacter, Enterococcus, Fusobacterium and Lachnospira. In addition, GA-g-CMCS fermentation significantly enhanced the production of short-chain fatty acids. These findings suggested that the digestive stability and prebiotic effect of CMCS were improved by grafting with GA.

Active/intelligent packaging films developed by immobilizing anthocyanins from purple sweetpotato and purple cabbage in locust bean gum, chitosan and κ-carrageenan-based matrices.

Active/intelligent packaging films were developed by incorporating purple sweetpotato anthocyanins (PSA) and purple cabbage anthocyanins (PCA) in locust bean gum/polyvinyl alcohol (LP), chitosan/polyvinyl alcohol (CP) and κ-carrageenan/polyvinyl alcohol (KP) film matrices. The joint effect of anthocyanins' source and polysaccharides' nature on the structure and functionality of the films was determined. Results showed PSA and PCA interacted with film matrices through hydrogen bonds and/or electrostatic interactions, resulting in improved film uniformity. PSA and PCA did not remarkably alter the water vapor permeability and tensile strength of the films; however, significantly improved the light barrier ability, antioxidant activity, pH-sensitivity and ammonia-sensitivity of films. For the films containing the same anthocyanins (PSA or PCA), LP-based films had relatively higher light barrier ability and storage stability, while CP-based had relatively weaker color changeable ability. When PSA and PCA were immobilized in the same film matrix, the films containing PCA had higher light barrier ability and antioxidant activity than the films containing PSA. Among the films, LP-PCA film exhibited a good potential to monitor the freshness of shrimp. Results suggested the structure and functionality of the films were influenced by the source of anthocyanins and the nature of polysaccharides.

Structure, stability and antioxidant activity of dialdehyde starch grafted with epicatechin, epicatechin gallate, epigallocatechin and epigallocatechin gallate.

BACKGROUND: Catechins, a member of the flavonoids, exist widely in teas, and have health benefits. However, catechins have poor stability, which greatly limits their application. In order to improve the stability of catechins, different catechins including (-)-epicatechin (EC), (-)-epicatechin gallate (ECG), (-)-epigallocatechin (EGC) and (-)-epigallocatechin gallate (EGCG) were conjugated onto dialdehyde starch by acid-mediated coupling method. The structure, stability and antioxidant activity of dialdehyde starch-catechin conjugates were determined. RESULTS: Thin-layer chromatography and ultraviolet-visible spectroscopy, fluorescence, nuclear magnetic resonance and infrared spectra revealed that catechins were successfully conjugated onto dialdehyde starch, coupling between 6-H/8-H of catechins' A ring and dialdehyde starch's aldehyde groups. The conjugates presented an amorphous structure and sheet-like and/or blocky morphologies. As compared to dialdehyde starch, the conjugates showed enhanced thermal stability. Furthermore, the stability of catechins in pH 7.4 phosphate-buffered saline was improved after conjugating onto dialdehyde starch. The conjugates exhibited significantly higher antioxidant activities than dialdehyde starch, decreasing in the following order: dialdehyde starch-ECG, dialdehyde starch-EGCG, dialdehyde starch-EC, dialdehyde starch-EGC and dialdehyde starch. CONCLUSION: Dialdehyde starch-catechin conjugates have great potential as stable antioxidant agents. © 2022 Society of Chemical Industry.

Effect of chitosan/starch aldehyde-catechin conjugate composite coating on the quality and shelf life of fresh pork loins.

BACKGROUND: Fresh pork is susceptible to oxidation and spoilage. Edible coating containing antioxidant and antimicrobial agents can create moisture and oxygen barriers around pork and inhibit oxidation and microbial growth in the pork. In this study, chitosan in combination with starch aldehyde-catechin conjugate (SACC) was used as a novel edible coating material for preserving fresh pork loins at chilled storage (4 ± 1 °C) for 14 days. Effect of chitosan/SACC composite coating on the quality of pork loins including weight loss, colour, pH value, microbial spoilage, lipid oxidation, protein oxidation, texture and sensory attributes during chilled storage was determined. RESULTS: Chitosan and SACC had synergistic antioxidant and antimicrobial actions. As compared with uncoated and chitosan coated pork loins, chitosan/SACC coated pork loins showed lower weight loss (7.16%), pH value (5.99), total viable count (7.11 log CFU g-1 ), total volatile base nitrogen content (130.2 mg kg-1 ), lipid oxidation level (0.47 mg malondialdehyde kg-1 ), protein oxidation level (0.047 mmol free thiol group g-1 ) and shear force (27.40 N) on day 14. Meanwhile, chitosan/SACC composite coating effectively maintained the colour, micro-structure and sensory attributes of pork loins throughout chilled storage period. The shelf life of pork loins was extended from 8 days (uncoated samples) to 14 days by chitosan/SACC composite coating. CONCLUSION: Chitosan/SACC composite coating effectively retarded the oxidation and spoilage of pork loins during chilled storage. © 2022 Society of Chemical Industry.

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.

Effect of Ferulic Acid-Grafted-Chitosan Coating on the Quality of Pork during Refrigerated Storage.

Pork is perishable due to oxidation and microbial spoilage. Edible coating based on biopolymers and phenolic compounds is an effective way to preserve the quality of pork. In this study, ferulic acid-grafted-CS (ferulic acid-g-CS) with strong antioxidant and antimicrobial activities was synthesized through a carbodiimide-mediated coupling reaction. The obtained ferulic acid-g-CS was used as an edible coating material for fresh pork. The effect of ferulic acid-g-CS coating on the quality of pork during storage was investigated at 4 °C for 8 days. As compared to the uncoated pork, pork coated with CS and ferulic acid-g-CS showed lower total viable counts, total volatile basic nitrogen values, pH values, thiobarbituric acid reactive substances, and drip losses. Besides, pork coated with CS and ferulic acid-g-CS presented more compact microstructures than the uncoated pork at the eighth day. Sensory evaluation assay showed pork coated with CS and ferulic acid-g-CS had better color, odor, and over acceptance in comparison with the uncoated pork. Ferulic acid-g-CS coating, due to its relatively higher antioxidant and antimicrobial activities compared to CS coating, had a better performance in refrigerated pork preservation. Ferulic acid-g-CS coating effectively extended the shelf life of refrigerated pork to 7 days. This study revealed ferulic acid-g-CS coating was a promising technology for refrigerated pork preservation.

Chitosan Films Functionalized with Different Hydroxycinnamic Acids: Preparation, Characterization and Application for Pork Preservation.

Hydroxycinnamic acids are one category of bioactive phenolic acids that are widely distributed in plants. In this study, chitosan (CS) was functionalized with three kinds of hydroxycinnamic acids (p-coumaric acid, caffeic acid and ferulic acid) through the carbodiimide-mediated grafting method. The obtained hydroxycinnamic-acid-grafted CSs (hydroxycinnamic acid-g-CSs) were further fabricated into food packaging films through solvent casting. For the first time, the functionalities of the different hydroxycinnamic acid-g-CS films were compared. Results showed the grafting ratio of p-coumaric acid-g-CS, caffeic acid-g-CS and ferulic acid-g-CS was 73.68, 129.42 and 91.75 mg/g, respectively. Instrumental analyses confirmed hydroxycinnamic acids conjugated with CS through amide and ester bonds. The functionalization of CS film with hydroxycinnamic acids produced a more compact microstructure and higher UV light barrier ability, mechanical strength, water vapor barrier ability, thermal stability and antioxidant and antimicrobial activities. Among the different hydroxycinnamic acid-g-CS films, caffeic acid-g-CS film presented the strongest barrier, mechanical, antioxidant and antimicrobial properties. Moreover, caffeic acid-g-CS film packaging effectively extended the shelf life of pork to 10 days at 4 °C. Our results suggest caffeic acid-g-CS film can be used in the active food packaging field.

Active packaging films and edible coatings based on polyphenol-rich propolis extract: A review.

The development of active packaging films and edible coatings based on biopolymers and natural bioactive substances has received increasing attention in recent years. Propolis, also called bee glue, is a natural resin substance collected by worker-bees from the mucilage, gum, and resin of several plants. In food industry, propolis is commonly extracted in solvents to afford polyphenol-rich extract with potent antimicrobial and antioxidant activities. The prepared propolis extract can be mixed with biopolymers, plasticizers, emulsifiers, and reinforcing agents to develop active packaging films and edible coatings. The functionality of active packaging films and edible coatings is closely related to the type, harvesting method, geographic origin, extraction method and extraction conditions of propolis, the content and composition of polyphenolic compounds in the extract, and the presence of other bioactive substances. Active packaging films and edible coatings based on propolis extract can impact the physical, biochemical, and sensory properties of food (e.g., fruits, vegetables, meat, and fish) during storage. This review focuses on the recent advances of active packaging films and edible coatings based on polyphenol-rich propolis extract. The impact of polyphenol-rich propolis extract on the structural characterization, functionality, and potential food applications of the films and edible coatings is summarized.

Highly efficient synthesis and characterization of starch aldehyde-catechin conjugate with potent antioxidant activity.

In this study, cassava starch aldehyde was functionalized with catechin through acid catalyzed condensation reaction. The structural characterization, stability and antioxidant activity of starch aldehyde-catechin conjugates were investigated. Thin layer chromatography revealed the conjugates did not contain free catechin. UV-vis spectra of the conjugates exhibited an absorption band at 280 nm, attributing to the B-ring of catechin moiety. Fourier-transform infrared and proton nuclear magnetic resonance spectroscopy demonstrated the conjugation occurred between the H-6/H-8 of catechin A-ring and the aldehyde groups of starch aldehyde. X-ray diffraction pattern indicated that the conjugates had an amorphous structure. Scanning electron microscopy showed the conjugates were fragmentary slices with rough surfaces. Notably, the conjugates were more stable than catechin in phosphate buffered saline (pH 7.4). In addition, the conjugates could not be digested in simulated saliva, gastric and small intestinal juices. The reducing power and free radical scavenging activity of starch aldehyde were remarkably elevated by conjugating with catechin. Meanwhile, the conjugates were non-cytotoxic to RAW264.7 mouse macrophage cells and possessed higher resistant starch contents than starch. Our results suggest starch aldehyde-catechin conjugates can be used as antioxidants in food industry.

Structure and functional properties of active packaging films prepared by incorporating different flavonols into chitosan based matrix.

Kaempferol, quercetin and myricetin are typical flavonols that feature different number of hydroxyl substituents at B-ring. In this study, kaempferol, quercetin and myricetin were individually mixed with chitosan (CS) based film matrix to develop active packaging films. Results showed the incorporation of flavonols produced dense inner microstructure by establishing intermolecular hydrogen bonding interactions with film matrix. The addition of flavonols reduced the water vapor permeability, oxygen permeability and UV-vis light transmittance of the films, whereas elevated the tensile strength, elongation at break, 2,2-diphenyl-1-picrylhydrazyl radical scavenging activity and antimicrobial activity of the films. Among all the films, the film containing myricetin showed the highest water vapor and oxygen barrier abilities and mechanical properties. Notably, different films presented distinct flavonol release behaviors in fatty and aqueous food stimulants. Kaempferol was easily released into fatty food stimulant, while myricetin was easily released into aqueous food stimulant. The release behavior of flavonols in different food stimulants greatly affected the antioxidant activity of the films. Our results suggest the structure and functional properties of the films are closely related to the number of hydroxyl substituents at B-ring of flavonols.

Development of multifunctional food packaging by incorporating betalains from vegetable amaranth (Amaranthus tricolor L.) into quaternary ammonium chitosan/fish gelatin blend films.

Multifunctional food packaging was prepared by incorporating betalains-rich vegetable amaranth (Amaranthus tricolor L.) extract into quaternary ammonium chitosan (QC)/fish gelatin (FG) blend films. The structures, physical and functional properties of the films with and without amaranth extract (AE) were determined. Results showed betalains-rich AE was pH-sensitive and could change its colors under alkaline conditions. Structural characterization revealed the interactions between AE and film matrix were based on hydrogen bonds, which influenced the compactness of the films. Notably, AE significantly enhanced the thickness (from 0.076 to 0.089 mm), UV-vis light barrier ability, elongation at break (from 66.7% to 88.8%), 2,2-diphenyl-1-picrylhydrazyl radical scavenging activity (from 6.8% to 95.8% at 5 mg/mL), antimicrobial activity against four foodborne pathogens (Escherichia coli, Staphylococcus aureus, Salmonella typhimurium and Listeria monocytogenes) and ammonia sensitivity of the films. However, AE remarkably reduced the water vapor permeability (from 34.9 × 10-11 to 26.4 × 10-11 g m-1 s-1 Pa-1) of the films. Notably, the films containing 5 wt% and 10 wt% of AE were suitable to monitor the freshness of shrimp. Our results suggested QC/FG films with betalains-rich AE could be used as antioxidant, antimicrobial and intelligent packaging in food industry.

Synthesis, characterization, antioxidant and antimicrobial activities of starch aldehyde-quercetin conjugate.

In this study, corn starch was functionalized with quercetin. Starch was first oxidized by sodium periodate to produce starch aldehyde, and then starch aldehyde was conjugated with quercetin through acid catalyzed condensation reaction. The structure, antioxidant and antimicrobial activities of starch aldehyde-quercetin conjugate were evaluated. Thin layer chromatography confirmed the conjugate did not contain free quercetin. The UV-vis spectrum of the conjugate exhibited an absorption band at 320 nm. Fourier-transform infrared and proton nuclear magnetic resonance spectra of the conjugate confirmed the aldehyde groups of starch aldehyde were involved in the conjugation reaction. X-ray diffraction pattern revealed the conjugate was in the amorphous state. Scanning electron microscopy observation showed the conjugate had sheet-like, virgate and round shapes. The structure of starch aldehyde-quercetin conjugate was different from that of native starch and starch aldehyde. As compared with native starch and starch aldehyde, starch aldehyde-quercetin conjugate exhibited higher reducing power, free radical scavenging activity and antimicrobial activity against Escherichia coli, Staphylococcus aureus, Salmonella and Listeria monocytogenes. Our results suggested starch aldehyde-quercetin conjugate could be developed as an antioxidant and antimicrobial agent in food industry.

Preparation and characterization of antioxidant packaging by chitosan, D-α-tocopheryl polyethylene glycol 1000 succinate and baicalein.

Baicalein (BN) is a kind of flavonoid with strong antioxidant ability. In this study, antioxidant packaging was developed by incorporating BN and D-α-tocopheryl polyethylene glycol 1000 succinate (TPGS) into chitosan (CS) film matrix for the first time. Effect of BN content (0.5 wt%, 1 wt% and 2 wt% on CS basis) on the structure, physical, release and antioxidant properties of CS-TPGS-BN films was investigated. Micro-structural observation showed 0.5 wt% of BN was compatible with film matrix, whereas 1 wt% and 2 wt% of BN reduced the homogeneity of the film. Fourier transform infrared spectroscopy revealed hydrogen bonds formed between BN and film matrix. X-ray diffraction showed the crystallinity of CS-TPGS film was increased by BN incorporation. The addition of BN remarkably increased the yellowness, water vapor and light barrier properties, opacity and antioxidant activity of the film. The release of BN from CS-TPGS-BN films to fatty food stimulant was demonstrated to fit second-order, Ritger-Peppas, and first-order models. Notably, CS-TPGS-BN films could effectively inhibit the oxidation of soybean oil during 28 days of storage. Thus, CS-TPGS-BN films could be used as novel antioxidant packaging for fatty foods.

Recent advances in the preparation, structural characteristics, biological properties and applications of gallic acid grafted polysaccharides.

Natural polysaccharides are important biopolymers with unique physicochemical properties and valuable biological activities. Due to the lack of sufficient functional groups, the applications of natural polysaccharides are incomparable to synthetic biopolymers. In order to broaden the applications of polysaccharides, gallic acid (GA, one kind of phenolic acid with numerous functional properties) has been grafted onto polysaccharides through several chemical and enzymatic methods. The structural characteristics and physical properties (e.g. water solubility, thermal stability, crystalline character and viscosity) of polysaccharides are greatly changed by grafting with GA. Meanwhile, GA grafted polysaccharides (GA-g-polysaccharides) show improved biological activities (e. g. antioxidant, antimicrobial, antitumor, anti-inflammatory, anti-allergic, enzyme inhibitory, prebiotic, and calcium oxalate crystals formation inhibitory effects) and broadened applications in the fields of active packaging, edible coating, encapsulation, delivery and bioadsorption. Notably, the structural characteristics, physical properties, biological activities and applications of GA-g-polysaccharides are affected by the grafting ratio and grafting method. Herein, recent advances of GA-g-polysaccharides in terms of preparation methods, structural characteristics, biological activities and potential applications are summarized. This review will provide a guideline for the scientific community towards more rational design and targeted use of GA-g-polysaccharides in the future.

Structural characterization and protective effect of gallic acid grafted O-carboxymethyl chitosan against hydrogen peroxide-induced oxidative damage.

In this study, gallic acid (GA) was grafted onto O-carboxymethyl chitosan (O-CMCS) by a free radical-mediated method. The synthesized GA grafted CMCS (GA-g-CMCS) was characterized by several instrumental methods and the antioxidant activity of the conjugate was evaluated by in vitro and cellular assays. Results showed the grafting ratio of GA-g-CMCS was 60.8 mg GAE/g. Thin layer chromatography and UV-vis, Fourier-transform infrared and proton nuclear magnetic resonance spectroscopic analyses all confirmed GA was successfully grafted onto O-CMCS. Meanwhile, covalent linkage formed between the amino group of O-CMCS and the carboxyl group of GA via amide bond. The 2,2-diphenyl-1-picrylhydrazyl radical scavenging activity and the reducing power of O-CMCS were remarkably improved by grafting with GA. Cellular assays showed GA-g-CMCS was non-toxic to RAW264.7 cells at 25-400 µg/mL. Moreover, GA-g-CMCS had a protective effect against hydrogen peroxide (H2O2)-induced oxidative damage in RAW264.7 cells. As compared with H2O2-treatment alone, the pretreatment of the cells with 100, 200 and 400 µg/mL of GA-g-CMCS significantly increased cell viability, reduced apoptosis and intracellular reactive oxygen species production, and improved membrane integrity and intracellular antioxidant enzyme (superoxide dismutase, catalase, glutathione peroxidase) activity. Our results suggested GA-g-CMCS could be developed as a novel antioxidant.

Development of antioxidant and antimicrobial packaging films based on chitosan and mangosteen (Garcinia mangostana L.) rind powder.

Mangosteen (Garcinia mangostana L.) rind has long been used as traditional medicine in Southeast Asian countries. Due to the presence of abundant polyphenols, mangosteen rind possesses potent antioxidant and antibacterial ability. In this study, mangosteen rind powder (MRP) was incorporated into chitosan (CS) film to develop active packaging for the first time. The structure, physical and functional properties of CS-MRP films containing different MRP contents (2.5, 5 and 10 wt% on CS basis) were determined. Fourier transform infrared spectroscopy revealed that the polyphenols in MRP could interact with CS through intermolecular hydrogen bonds. X-ray diffraction analysis showed the crystallinity of CS-MRP films was higher than that of CS film. Notably, MRP incorporation significantly increased the thickness, tensile strength, and UV-visible light barrier, antioxidant and antibacterial properties of CS film. However, the moisture content, water solubility, water vapor barrier ability and elongation at break of CS film were reduced by MRP incorporation. Moreover, CS-MRP film packaging effectively inhibited the increase in the peroxide value and thiobarbituric acid reactive substances of soybean oil during storage. Our results suggested CS-MRP films could be used as active packaging to increase the oxidative stability of soybean oil in food industry.