Development of smart colorimetric indicators for tracking kimchi freshness by loading aronia extract in agar, κ-carrageenan, and cellulose nanofiber films.

Color indicator films incorporating aronia extract powder (AEP) and biopolymers like agar, carrageenan, and cellulose nanofiber (CNF) were developed to monitor kimchi freshness. AEP-containing films showed strong UV-barrier properties, and reduced light transmittance by 99.12 % for agar, 98.86 % for carrageenan, and 98.67 % for CNF-based films. All AEP-films exhibited high sensitivity to pH changes and vapor exposure to ammonia and acetic acid. Color change notably influenced by the polymer type, particularly evident with ammonia vapor exposure, especially in the AEP/carrageenan film. The chemical structure and thermal stability of the biopolymers remained unchanged after AEP-addition. Tensile strength increased by 24.2 % for AEP/CNF but decreased by 19.4 % for AEP/agar and 24.3 % for AEP/carrageenan films. AEP-containing films displayed strong antioxidant activity, with 99 % free radical scavenging in ABTS and ~ 80 % in DPPH assays. Alkalized AEP-indicator films were more effective in detecting color changes during kimchi packaging tests. Among the labels, alkalized AEP/agar film showed the most obvious color change from green-gray (fresh kimchi, pH 5.5, acidity 0.48 %) to pale brown (optimal fermentation, pH 4.6, acidity 0.70 %), and pale violet-brown (over-fermented, pH 3.80, acidity 1.35 %). Alkalized AEP-indicator films offer promising real-time detection of packed fermented foods like kimchi.

pH-sensitive smart indicators based on cellulose and different natural pigments for tracing kimchi ripening stages.

Five natural pigments including water-soluble [butterfly pea (BP), red cabbage (RC), and aronia (AR)] and alcohol-soluble [shikonin (SK) and alizarin (ALZ)] were extracted, characterized, and loaded onto cellulose for preparing pH-sensitive indicators. The indicators were tested for their color response efficiency, gas sensitivity, response to lactic acid, color release, and antioxidant activity. Cellulose-water soluble indicators showed more obvious color changes than alcohol-soluble indicators in lactic acid solution and pH solutions (1-13). All cellulose-pigment indicators exhibited prominent sensitivity to ammonia compared to acidic vapor. Antioxidant activity and release behavior of the indicators were influenced by pigment type and simulants. Kimchi packaging test was carried out using original and alkalized indicators. The alkalized indicators were more effective in showing visible color changes during kimchi storage than the original indicators, and cellulose-ALZ displayed the most distinct color change from violet (fresh kimchi, pH 5.6, acidity 0.45 %) to gray (optimum fermented kimchi, pH 4.7, acidity 0.72 %), and to yellow (over fermented kimchi, pH 3.8, acidity 1.38 %) which followed by BP, AR, RC, SK respectively. The findings of the study suggest that the alkalization method could be used to show noticeable color changes in a narrow pH range for application with acidic foods.

Antimicrobial, antioxidant, and pH-sensitive polyvinyl alcohol/chitosan-based composite films with aronia extract, cellulose nanocrystals, and grapefruit seed extract.

Aronia or black chokeberry (Aronia melanocarpa), cellulose nanocrystals (CNCs), and grapefruit seed extract (GSE) were used for the preparation of multifunctional polyvinyl alcohol/chitosan (PVA/CS) composite films with pH-sensitivity, antimicrobial, antioxidant, and UV-barrier properties. Aronia extract showed total phenolic content of 297 ± 0.5 µg GAE/mg aronia extract, potent antioxidant activity, and high color-response efficiency. Isolated CNCs showed a needle-like structure with a length of 470 nm and a width of 35 nm. The tensile strength of the PVA/CS composite film increased by 74% after the incorporation of CNCs, whereas the film flexibility was enhanced by 75% after adding GSE. The PVA/CS-A (aronia extract) composite film showed a significant color change at different pHs and potent antioxidant activity. At the same time, the PVA/CS-G (GSE) showed the highest antimicrobial activity against Escherichia coli (Gram-negative) and Listeria monocytogenes (Gram-positive) bacteria. The PVA/CS-CGA composite film, reinforced with CNCs/GSE/Aronia extract, showed the highest UV-barrier (95.5%), highest antioxidant activity (95%), potent antimicrobial activity, pH-sensitivity, lowest water vapor permeability (WVP), and desirable mechanical properties. The multifunctional properties of the produced composite films encourage their use as active and intelligent food packaging films to extend shelf life and monitor food quality.

Multifunctional poly(vinyl alcohol) films using cellulose nanocrystals/oregano and cellulose nanocrystals/cinnamon Pickering emulsions: Effect of oil type and concentration.

Poly (vinyl alcohol) (PVA) films with high transparency, UV-barrier, antioxidant, and antimicrobial properties were prepared using oregano essential oil (OEO) and cinnamon essential oil (CEO) Pickering emulsions. The effect of Pickering emulsion type and concentration on the PVA film properties was studied. Cellulose nanocrystals (CNCs) were used as a natural stabilizer to prepare OEO and CEO Pickering emulsions. Both emulsions showed spherical droplets with diameters of 155-291 nm, zeta potential of -36.2 to -49.6 mV, minimum inhibition concentration of 6.25-12.5 µL/mL, and inhibition zone of 40-65 mm, depending on oil type. Morphology and FTIR analysis showed that OEO and CEO Pickering emulsions were compatible with the PVA matrix. The UV-transmittance of PVA films decreased from 77.3% to 30.4% and 2.0% without sacrificing the transparency after adding OEO and CEO Pickering emulsions, respectively. Antimicrobial results showed that E. coli was more sensitive to CEO, while S. aureus was sensitive to OEO Pickering emulsion. PVA/CEO film displayed higher properties than PVA/OEO film.

Preparation of multifunctional carboxymethyl cellulose-based films incorporated with chitin nanocrystal and grapefruit seed extract.

Chitin nanocrystals (ChNC) were isolated from shrimp shells powder using acid hydrolysis and ammonium persulfate methods. Multifunctional carboxymethyl cellulose (CMC) composite films were prepared by adding ChNC and grapefruit seed extract (GSE), and their effects on the optical, mechanical, water vapor barrier, and antibacterial properties of CMC film were investigated. The isolated ChNC had a needle-like structure with a length of 340-370 nm and a diameter of 18-20 nm depending on the isolation method. The CMC films prepared with ChNC and GSE were transparent with high UV barrier properties. The addition of GSE reduced the strength (TS) and stiffness (EM) of CMC films by 10.4% and 30.3%, respectively, while the flexibility (EB) increased by 17.7%. However, when the ChNC was added, the TS and EM of CMC film increased by 19.7% and 58.7%, respectively, and the EB remained the same. The addition of ChNC reduced the water vapor permeability (WVP) of the CMC film by 27%. CMC films containing GSE also showed strong antibacterial activity against foodborne pathogenic bacteria, E. coli and L. monocytogenes.

Multifunctional nanocellulose/metal and metal oxide nanoparticle hybrid nanomaterials.

Nanocellulose materials are derived from cellulose, the most abundant biopolymer on the earth. Nanocellulose have been extensively used in the field of food packaging materials, wastewater treatment, drug delivery, tissue engineering, hydrogels, aerogels, sensors, pharmaceuticals, and electronic sectors due to their unique chemical structure and excellent mechanical properties. On the other hand, metal and metal oxide nanoparticles (NP) such as Ag NP, ZnO NP, CuO NP, and Fe3O4 NP have a variety of functional properties such as UV-barrier, antimicrobial, and magnetic properties. Recently, nanocelluloses materials have been used as a green template for producing metal or metal oxide nanoparticles. As a result, multifunctional nanocellulose/metal or metal oxide hybrid nanomaterials with high antibacterial properties, ultraviolet barrier properties, and mechanical properties were prepared. This review emphasized recent information on the synthesis, properties, and potential applications of multifunctional nanocellulose-based hybrid nanomaterials with metal or metal oxides such as Ag NP, ZnO NP, CuO NP, and Fe3O4 NP. The nanocellulose-based hybrid nanomaterials have huge potential applications in the area of food packaging, biopharmaceuticals, biomedical, and cosmetics.

Effect of isolation methods of chitin nanocrystals on the properties of chitin-silver hybrid nanoparticles.

Chitin nanocrystal (ChNC) was isolated using sulfuric acid hydrolysis (ChNCH2SO4), TEMPO-oxidation (ChNCTEMPO), and ammonium persulfate (ChNCAPS) methods, and used for the preparation of hybrid nanoparticles of ChNC/silver nanoparticles (AgNP). The ChNC exhibited a needle-shaped structure with a sulfate group content of 135 µmol/g for ChNCH2SO4 and carboxyl content of 0.71 and 1.42 mmol/g for ChNCTEMPO and ChNCAPS, respectively. ChNC worked as a reducing and stabilizing agent for the production of AgNP and reduced the size of AgNP from 23.9 nm to 6.3 nm in the ChNC/AgNP hybrid. The carboxyl content of ChNC played a significant role for the nucleation, size distribution, and antibacterial activity of ChNC/AgNP. ChNC/AgNP hybrid, especially ChNCAPS/AgNP, exhibited strong antibacterial activity against food-borne pathogenic Gram-negative (E. coli) and Gram-positive (L. monocytogenes) bacteria. The prepared ChNC/AgNP hybrid nanomaterials have a high potential for the application to be used as a nanofiller to improve the properties of food packaging materials to extend the shelf-life of packaged food.

Preparation of antimicrobial hybrid nano-materials using regenerated cellulose and metallic nanoparticles.

In this study, antimicrobial hybrid nano-materials were prepared by one-pot syntheses of silver (Ag), copper oxide (CuO), or zinc oxide (ZnO) nanoparticles (NPs) during regeneration of cellulose from cotton linter (CL) and microcrystalline cellulose (MCC). SEM micrographs indicated that the metallic nanoparticles were attached to the surface of the regenerated cellulose. EDX and ICP results showed that more AgNPs were adsorbed on the cellulose than CuONPs or ZnONPs. FTIR results revealed that the metallic nanoparticles were attached to the cellulose through the interaction with the hydroxyl group of cellulose. XRD results showed the characteristic diffraction peaks of individual metallic nanoparticles. The thermal stability of the R-CL and R-MCC increased in the hybrids with AgNPs and ZnONPs. The R-cellulose/metallic NPs hybrids showed strong antibacterial activity against E. coli and L. monocytogenes. Thus, the hybrid nano-materials can be used as nanofillers for the preparation of antibacterial packaging films.

Effect of oxidized chitin nanocrystals isolated by ammonium persulfate method on the properties of carboxymethyl cellulose-based films.

Oxidized chitin nanocrystals (ChNCs) were isolated from crab shell chitin using ammonium persulfate (APS) method. The oxidized ChNCs were in needle shape with a diameter of 15nm, the length of 400-500nm, and crystallinity index of 93.5%. Carboxymethyl cellulose (CMC)-based films reinforced with the ChNCs (0, 1, 5, and 10wt.%) were flexible and transparent. The mechanical strength of the CMC film increased significantly (p<0.05) after blending with the ChNCs. The tensile strength (TS) and elastic modulus (EM) increased by 88% and 243% when 10wt.% of ChNCs were incorporated. Water vapor barrier property of the composite films decreased and the hydrophilicity increased compared with the neat CMC film. The oxidized ChNCs obtained using the APS method have a high potential for being used as a reinforcing filler to improve the mechanical properties of nanocomposite films for the application in food packaging, nano-papers, hydrogels as well as biomedical applications.

Characterization of carboxymethyl cellulose-based nanocomposite films reinforced with oxidized nanocellulose isolated using ammonium persulfate method.

Cellulose nanocrystals (CNCs) were isolated from cotton linter (CL) and microcrystalline cellulose (MCC) using an ammonium persulfate (APS) method for a simultaneous isolation and oxidation of CNCs. The CNCs were in rod-like shape with a diameter of 10.3nm and 11.4nm, a length of 120-150nm and 103-337nm, a crystallinity index of 93.5% and 79.1% for the CNCCL and CNCMCC, respectively. The suspensions of oxidized CNCs were transparent and stable with the zeta potential values of -50.6mV and -46.9mV. The CNCs were uniformly distributed within the carboxymethyl cellulose (CMC) polymer matrix. The tensile strength (TS) increased by 102% and 73%, and elastic modulus (E) increased by 228% and 166% with the incorporation of at 10wt% of CNCCL and CNCMCC, respectively. Conclusively, the CNCCL showed a more uniform particle size distribution, higher crystallinity, transparency, thermal stability, and superior mechanical strength compared with the CNCMCC.

Preparation of multifunctional chitin nanowhiskers/ZnO-Ag NPs and their effect on the properties of carboxymethyl cellulose-based nanocomposite film.

Chitin nanowhiskers (ChNW) were isolated and used for the synthesis of hybrid ChNW/ZnO-Ag NPs. The hybrid nanoparticles were used for the preparation of multifunctional carboxymethyl cellulose (CMC) films. A ChNW was needle shape with the width of 8-40nm, the length of 150-260nm, and crystallinity index of 93.6%. The ZnO-Ag NPs were spherical with the diameter of 10.5-16.2nm. STEM, EDX, XRD, and UV-vis analyses confirmed the formation of ZnO-Ag NPs on the surface of ChNW. The thermal stability of ChNW was increased by incorporation of ZnO-Ag NPs. A CMC-based nanocomposite film incorporated with 5wt% of ChNW/ZnO-Ag NPs was homogeneous and showed the high UV-barrier property. The tensile strength (TS) and elastic modulus (E) of the composite film increased by 18-32% and 55-100%, respectively, while the elongation at break (EB) decreased by 23-33%. CMC composite films showed strong antibacterial activity against E. coli and L. monocytogenes.

Isolation of cellulose nanocrystals from grain straws and their use for the preparation of carboxymethyl cellulose-based nanocomposite films.

Cellulose nanocrystals (CNCs) were isolated from rice straw (RS), wheat straw (WS), and barley straw (BS) by using acid hydrolysis method. They were fibrous in shape with length (L) of 120-800nm and width (W) of 10-25nm, aspect ratio (L/W) of 18, 16 and 19, crystallinity index (CI) of 0.663, 0.710, and 0.634, and yield of 64, 75, and 69wt% for RS, WS, and BS respectively. Carboxymethyl cellulose (CMC)/CNC composite films were prepared with various concentration of the CNCs. SEM results showed that the CNCs were evenly distributed in the polymer to form homogeneous films. Mechanical and water vapor barrier properties were varied depending on the type of CNCs and their concentration. Tensile strength (TS) increased by 45.7%, 25.2%, and 42.6%, and the water vapor permeability (WVP) decreased by 26.3%, 19.1%, and 20.4% after forming composite with 5wt% of CNCs obtained from RS, WS, and BS, respectively.

Effect of post-treatments and concentration of cotton linter cellulose nanocrystals on the properties of agar-based nanocomposite films.

Cellulose nanocrystals (CNCs) were prepared by acid hydrolysis of cotton linter pulp fibers and three different purification methods, i.e., without post purification (CNC1), dialyzed against distilled water (CNC2), and neutralized with NaOH (CNC3), and their effect on film properties was evaluated by preparation of agar/CNCs composite films. All the CNCs were rod in shape with diameter of 15-50 nm and length of 210-480 nm. FTIR result indicated that there was no distinctive differences in the chemical structure between CNCs and cotton linter cellulose fiber. No significant relationship was observed between the sulfate content and crystallinity index of CNCs. The CNC3 showed higher thermal stability than the other type of CNCs due to the less adverse effect on the thermal stability of sulfate groups induced by the neutralization with NaOH. The tensile strength (TS) of agar film increased by 15% with incorporation of 5 wt% of CNC3, on the contrary, it decreased by 10% and 15% with incorporation of CNC1 and CNC2, respectively. Other performance properties of agar/CNCs composite films such as optical and water vapor barrier properties showed that the CNC3 was more effective filler than the other CNCs. In the range of concentration of CNC3 tested (1-10 wt%), inclusion of 5 wt% of CNC3 was the maximum concentration for improving or maintaining film properties of the composite films. The neutralization of acid hydrolyzed cellulose using NaOH was simple and convenient for the preparation of CNC and bionanocomposite films.

Preparation and characterization of sodium carboxymethyl cellulose/cotton linter cellulose nanofibril composite films.

Crystalline cellulose nanofibril (CNF) was isolated from cotton linter pulp using an acid hydrolysis method and used as a filler to reinforce sodium carboxymethyl cellulose (CMC) film. The CNF was in rod shape with the diameter of 23-38 nm and the length of 125-217 nm and crystallinity index (CI) was 0.89. The effect of CNF concentration (1, 3, 5, and 10 wt% based on CMC) on the optical, morphological, mechanical, water vapor barrier, surface hydrophobicity, and thermal properties of the nanocomposites were studied. The CNF was evenly distributed in the polymer matrix to form smooth and flexible films indicating the CNF is highly compatible with the CMC. The tensile strength (TS) and elastic modulus (EM) of CMC film increased by 23% and 27%, respectively, while the elongation (E) decreased by 28% with 5 wt% of CNF inclusion. The WVP of CMC film decreased at low content of CNF, and increased with increase in CNF content, then decreased but to the same level of the control CMC film with the inclusion of 10 wt% of CNF. Transparency of CMC film decreased slightly from 87.7% to 86.2% with 5 wt% of CNF. The CMC/CNF composite films have a high potential to be used as an edible coating or packaging films for the extension of shelf life of fresh and minimally processed fruits and vegetables.