Retaining Oxidative Stability of Emulsified Foods by Novel Nonmigratory Polyphenol Coated Active Packaging

Exploring chitosan-plant extract bilayer coatings: Advancements in active food packaging via polypropylene modification

UV-ozone activated polypropylene (PP) food films were subjected to a novel bilayer coating process involving primary or quaternary chitosan (CH/QCH) as the first layer and natural extracts from juniper needles (Juniperus oxycedrus; JUN) or blackberry leaves (Rubus fruticosus; BBL) as the second layer. This innovative approach aims to redefine active packaging (AP) development. Through a detailed analysis by surface characterization and bioactivity assessments (i.e., antioxidant and antimicrobial functionalities), we evaluated different coating combinations. Furthermore, we investigated the stability and barrier characteristics inherent in these coatings. The confirmed deposition, coupled with a comprehensive characterization of their composition and morphology, underscored the efficacy of the coatings. Our investigation included wettability assessment via contact angle (CA) measurements, X-ray photoelectron spectroscopy (XPS), and attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR), which revealed substantial enhancements in surface concentrations of elements and functional groups of CH, QCH, JUN, and BBL. Scanning electron microscopy (SEM) unveiled the coatings' heterogeneity, while time-of-flight secondary ion mass spectrometry (ToF-SIMS) and CA profiling showed moderately compact bilayers on PP, providing active species on the hydrophilic surface, respectively. The coatings significantly reduced the oxygen permeability. Additionally, single-layer depositions of CH and QCH remained below the overall migration limit (OML). Remarkably, the coatings exhibited robust antioxidative properties due to plant extracts and exceptional antimicrobial activity against S. aureus, attributed to QCH. These findings underscore the pivotal role of film surface properties in governing bioactive characteristics and offer a promising pathway for enhancing food packaging functionality.

Methods to evaluate the scavenging activity of antioxidants toward reactive oxygen and nitrogen species (IUPAC Technical Report)

This project was aimed to identify the quenching chemistry of biologically important reactive oxygen and nitrogen species (ROS/RNS, including radicals), to show antioxidant action against reactive species through H‐atom and electron transfer reactions, and to evaluate the ROS/RNS scavenging activity of antioxidants with existing analytical methods while emphasizing the underlying chemical principles and advantages/disadvantages of these methods. In this report, we focused on the applications and impact of existing assays on potentiating future research and innovations to evolve better methods enabling a more comprehensive study of different aspects of antioxidants and to provide a vocabulary of terms related to antioxidants and scavengers for ROS/RNS. The main methods comprise the scavenging activity measurement of the hydroxyl radical (•OH), dioxide(•1–) (O2 •–: commonly known as the superoxide radical), dihydrogen dioxide (H2O2: commonly known as hydrogen peroxide), hydroxidochlorine (HOCl: commonly known as hypochlorous acid), dioxidooxidonitrate(1–) (ONOO−: commonly known as the peroxynitrite anion), and the peroxyl radical (ROO•). In spite of the diversity of methods, there is currently a great need to evaluate the scavenging activity of antioxidant compounds in vivo and in vitro. In addition, there are unsatisfactory methods frequently used, such as non-selective UV measurement of H2O2 scavenging, producing negative errors due to incomplete reaction of peroxide with flavonoids in the absence of transition metal ion catalysts. We also discussed the basic mechanisms of spectroscopic and electrochemical nanosensors for measuring ROS/RNS scavenging activity of antioxidants, together with leading trends and challenges and a wide range of applications. This project aids in the identification of reactive species and quantification of scavenging extents of antioxidants through various assays, makes the results comparable and more understandable, and brings a more rational basis to the evaluation of these assays and provides a critical evaluation of existing ROS/RNS scavenging assays to analytical, food chemical, and biomedical/clinical communities by emphasizing the need for developing more refined, rapid, simple, and low‐cost assays and thus opening the market for a wide range of analytical instruments, including reagent kits and sensors.

Integrating Antioxidant Functionality into Polymer Materials: Fundamentals, Strategies, and Applications

While antioxidants are widely known as natural components of healthy food and drinks or as additives to commercial polymer materials to prevent their degradation, recent years have seen increasing interest in enhancing the antioxidant functionality of newly developed polymer materials and coatings. This paper provides a critical overview and comparative analysis of multiple ways of integrating antioxidants within diverse polymer materials, including bulk films, electrospun fibers, and self-assembled coatings. Polyphenolic antioxidant moieties with varied molecular architecture are in the focus of this Review, because of their abundance, nontoxic nature, and potent antioxidant activity. Polymer materials with integrated polyphenolic functionality offer opportunities and challenges that span from the fundamentals to their applications. In addition to the traditional blending of antioxidants with polymer materials, developments in surface grafting and assembly via noncovalent interaction for controlling localization versus migration of antioxidant molecules are discussed. The versatile chemistry of polyphenolic antioxidants offers numerous possibilities for programmed inclusion of these molecules in polymer materials using not only van der Waals interactions or covalent tethering to polymers, but also via their hydrogen-bonding assembly with neutral molecules. An understanding and rational use of interactions of polyphenol moieties with surrounding molecules can enable precise control of concentration and retention versus delivery rate of antioxidants in polymer materials that are critical in food packaging, biomedical, and environmental applications.

Multilayers assembly of bio-polyelectrolytes onto surface modified polypropylene films: Characterization, chelating and antioxidant activity

In order to remove the trace transition metal ions which catalyze the oxidation in food, chitosan (CS) and sodium alginate (ALG) multilayers were assembled on the polypropylene (PP) surface grafted with polyacrylic acid (PAA) to obtain PP-g-PAA/(CS/ALG)_n films. The morphology of the active films was observed, and the thickness of each single assembled layer was about 7 nm. The chelation ability of the films improved with increasing number of (CS/ALG)_n multilayers, and Cu²⁺ chelating quantity of PP-g-PAA/(CS/ALG)_15.5 films was about 3.4 umol/cm² for 72 h at pH about 5, improved by about 9.92 % as compared with PP-g-PAA films. In addition, the PP-g-PAA/(CS/ALG)_n films had chelation activity for both Cu²⁺ and Fe²⁺, suggesting the potentiality in antioxidant food package application.

Reactive Extrusion of Nonmigratory Antioxidant Poly(lactic acid) Packaging

Reactive extrusion of bio-derived active packaging offers a new approach to address converging concerns over environmental contamination and food waste. Herein, metal-chelating nitrilotriacetic acid (NTA) ligands were grafted onto poly(lactic acid) (PLA) by reactive extrusion to produce metal-chelating PLA (PLA-g-NTA). Radical grafting was confirmed by attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy with the introduction of secondary alkyl stretches (2919 and 2860 cm^-1) and by X-ray photoelectron spectroscopy (XPS) with an increase in the atomic percentage of nitrogen. Compared to films prepared from native, granular PLA (gPLA), PLA-g-NTA films had lower contact angles and hysteresis values (86.35° ± 2.49 and 31.89° ± 2.27 to 79.91° ± 1.58 and 21.79° ± 1.72, respectively), supporting the surface orientation of the NTA ligands. The PLA-g-NTA films exhibited a significant antioxidant character with a radical scavenging capacity of 0.675 ± 0.026 nmol Trolox_(eq)/cm² and an iron chelation capacity of 54.09 ± 9.36 nmol/cm². PLA-g-NTA films delayed ascorbic acid degradation, retaining ∼45% ascorbic acid over the 9-day study compared to <20% for control PLA. This research makes significant advances in translating active packaging technologies to bio-derived materials using scalable, commercially translatable synthesis methods.

Valorization of Carob Fruit Residues for the Preparation of Novel Bi-Functional Polyphenolic Coating for Food Packaging Applications

The food industry has become interested in the development of innovative biomaterials with antioxidant and antimicrobial properties. Although several biopolymers have been evaluated for food packaging, the use of polyphenolic coatings has been unexplored. The purpose of this work was to develop an antioxidant and antimicrobial coating for food packaging through the polymerization of carob phenolics. At first, the polyphenolic coatings were deposited in glass surfaces polymerizing different concentrations of carob extracts (2 and 4 mg mL⁻¹) at three pH values (7, 8 and 9). Results demonstrated that the coating produced at pH 8 and at a concentration of 4 mg mL⁻¹ had the most potent antioxidant and antimicrobial potential. Then, the coating was applied directly on the salmon fillet (coating) and on the plastic container (active packaging). Peroxide and thiobarbituric acid-reactive substances (TBARS) methods were used to measure the potency to inhibit lipid oxidation in salmon fillets. Furthermore, the anti-Listeria activity of coatings was also assessed. Results showed a significant decrease of lipid oxidation during cold storage of salmon fillets for both treatments; the superiority of applied coating directly on the salmon fillets was also highlighted. Regarding the antimicrobial potency, the polyphenolic coating depleted the growth of Listeria monocytogenes after 10 days storage; while the active packaging had no effect on Listeria monocytogenes. Overall, we describe the use of low-cost carob polyphenols as precursors for the formation of bifunctional coatings with promising applications in food packaging.

The Role of Solid Support Bound Metal Chelators on System-Dependent Synergy and Antagonism with Nisin

Active packaging can enhance the performance of natural antimicrobials in controlling food spoilage and waste, while addressing consumer demands for cleaner labels. Yet, synergies are system dependent, with some conditions counterintuitively promoting antagonistic effects. In particular, metal chelators can improve performance of certain natural antimicrobials and have been incorporated in nonmigratory metal chelating active packaging technologies. However, the influence of chelating ligand chemistry on antimicrobial efficacy has not been investigated in microbial spoilage models. The effect of three commercial chelating resins on the growth of Alicyclobacillus acidoterrestris ATCC 49025, a thermoduric acidophilic spore-former, in growth media and apple juice was investigated. Dowex MAC-3, Chelex 100, and Lewatit TP260 were used as models for metal chelating active packaging containing carboxylic acid (CA), iminodiacetic acid (IDA), and aminomethylphosphonic acid (AMPA) ligands. Diameters (CA = 472.4 ± 117.2 μm, IDA = 132.93 ± 26.71 μm, and AMPA = 498.3 ± 29.24 μm), dissociation kinetics (CA = 6.44 ± 0.109, IDA = -0.977 ± 9.94, AMPA = 7.43 ± 0.193), and metal chelating capacities (CA = 1.16 × 10^-4 mol/g, IDA = 1.52 × 10^-3  mol/g, and AMPA = 4.67 × 10^-4 mol/g) were used to distinguish differences in antimicrobial efficacies. Growth of A. acidoterrestris in acidified Potato Dextrose Broth over 24 hr with chelating resins indicated early death phase for CA and IDA resins and bactericidal for AMPA resin. However, viability in commercial apple juice with the inclusion of nisin and chelating resins was variable, with IDA resin significantly (P < 0.05) increasing viability while the effect of CA and AMPA resins remained elusive. This work emphasizes the importance of biological repeatability and correct statistical modeling in identifying conditions under which the antimicrobial intervention of nisin in real food systems, such as acidic beverages and juices, are synergistic or antagonistic. PRACTICAL APPLICATION: New technologies to control microbial food spoilage and waste need to be explored to address consumers on-going demands for reducing additive use.  Solid support bound metal chelators can both promote and control microbial growth when used in conjunction with nisin, a natural antimicrobial.  This work explores how system conditions can render a given technology either synergistic or antagonistic, and highlights the importance of sufficient biological replicates in experimental design.

Photocurable coatings prepared by emulsion polymerization present chelating properties

Herein, we present a method to synthesize a photocurable metal chelating copolymer coating via emulsion polymerization to enable a facile coat/cure preparation of metal chelating materials. The copolymer coating was a poly(n-butyl acrylate) based polymer (79 mol %) synthesized by emulsion polymerization, with iminodiacetic acid (2 mol %) and benzophenone moieties (19 mol %) to impart metal chelating and photocrosslinking properties, respectively. The copolymer was applied onto polypropylene films and was photocured (365 nm, 225 mW/cm², 180 s) to produce metal chelating film. The resulting metal chelating film had activity towards Fe³⁺ by chelating 10.9 ± 1.9 nmol/cm², 47.9 ± 5.3 nmol/cm², and 156.0 ± 13.8 nmol/cm² of Fe³⁺ at pH 3.0, pH 4.0, and pH 5.0, respectively. The metal chelating film controlled transition metal induced ascorbic acid degradation by extending half-life of ascorbic acid degradation from 6 days to 20 days at pH 3.0, and from 3 days to 6 days at pH 5.0, demonstrating its potential as an antioxidant active packaging material. Despite the introduction of polar iminodiacetic acid chelating moieties, the poly(n-butyl acrylate) based coatings retained low surface energies (24.0 mN/m) necessary to mitigate fouling and enable product release in packaging applications. This work overcomes a major knowledge gap in the area of functional coatings, by demonstrating a method by which critical properties such as control of surface energy, retention of mechanical properties, and scalability are integrated into the structure of a functional coating. The photocurable polymer coatings as reported here enable scalable production of active materials with metal chelating functionality, with applications in water treatment, trace metal detection, protein purification, and active packaging.

Photo-Curable Metal-Chelating Coatings Offer a Scalable Approach to Production of Antioxidant Active Packaging

Synthetic metal chelators (for example, ethylenediaminetetraacetic acid, EDTA) are widely used as additives to control trace transition metal induced oxidation in consumer products. To enable removal of synthetic chelators in response to increasing consumer demand for clean label products, metal-chelating active food packaging technologies have been developed with demonstrated antioxidant efficacy in simulated food systems. However, prior work in fabrication of metal-chelating materials leveraged batch chemical reactions to tether metal-chelating ligands, a process with limited industrial translatability for large-scale fabrication. To improve the industrial translatability, we have designed a 2-step laminated photo-grafting process to introduce metal chelating functionality onto common polymeric packaging materials. Iminodiacetic acid (IDA) functionalized materials were fabricated by photo-grafting poly(acrylic acid) onto polypropylene (PP) films, followed by a second photo-grafting process to graft-polymerize an IDA functionalized vinyl monomer (GMA-IDA). The photo-grafting was conducted under atmospheric conditions and was completed in 2 min. The resulting IDA functionalized metal-chelating material was able to chelate iron and copper, and showed antioxidant efficacy against ascorbic acid degradation, supporting its potential to be used synergistically with natural antioxidants for preservation of food and beverage products. The 2-step photo-grafting process improves the throughput of active packaging coatings, enabling potential roll-to-roll fabrication of metal-chelating active packaging materials for antioxidant food packaging applications.

PRACTICAL APPLICATION

To address consumer and retail demands for "clean label" foods and beverages without a corresponding loss in product quality and shelf life, producers are seeking next generation technologies such as active packaging. In this work, we will report the synthesis of metal-chelating active packaging films, which enable removal of the synthetic additive, ethylenediamine tetraacetic acid. The new synthesis technique improves the throughput of metal-chelating active packaging coatings, enabling potential roll-to-roll fabrication of the materials for antioxidant food packaging applications.