Natural biopolymer-based nanocomposite films for packaging applications

Concerns on environmental waste problems caused by non-biodegradable petrochemical-based plastic packaging materials as well as the consumer's demand for high quality food products has caused an increasing interest in developing biodegradable packaging materials using annually renewable natural biopolymers such as polysaccharides and proteins. Inherent shortcomings of natural polymer-based packaging materials such as low mechanical properties and low water resistance can be recovered by applying a nanocomposite technology. Polymer nanocomposites, especially natural biopolymer-layered silicate nanocomposites, exhibit markedly improved packaging properties due to their nanometer size dispersion. These improvements include increased modulus and strength, decreased gas permeability, and increased water resistance. Additionally, biologically active ingredients can be added to impart the desired functional properties to the resulting packaging materials. Consequently, natural biopolymer-based nanocomposite packaging materials with bio-functional properties have a huge potential for application in the active food packaging industry. In this review, recent advances in the preparation of natural biopolymer-based films and their nanocomposites, and their potential use in packaging applications are addressed.     

Chitosan-based biodegradable functional films for food packaging applications

Chitin is the structural material of crustaceans, insects, and fungi, and is the second most abundant biopolymer after cellulose on earth. Chitosan, a deacetylated derivative of chitin, can be obtained by deacetylation of chitin. It is a functionally versatile biopolymer due to the presence of amino groups responsible for the various properties of the polymer. Although it has been used for various industrial applications, the recent one is its use as a biodegradable antimicrobial food packaging material. Much research has been focused on chitosan-based flexible food packaging and edible food coatings to compete with conventional non-biodegradable plastic-based food packaging materials. Various strategies have been used to improve the properties of chitosan - using plasticizers and cross-linkers, embedding the polymer with fillers such as nanoparticles, fibers, and whiskers, and blending the polymer with natural extracts and essential oils and also with other natural and synthetic polymers. However, much research is still needed to bring this biopolymer to industrial levels for the food packaging applications.Industrial relevanceAs a major by-product of the seafood industry, a massive amount of crustacean shell waste is generated each year, which can be used to produce value-added chitin, which can be converted to chitosan using a relatively simple deacetylation process. Being extracted from a bio-waste product using many energy-efficient methods, chitosan is much cheaper as compared to other biopolymers. Nevertheless, the exceptional properties of chitosan make it a relatively stronger candidate for food packaging applications. Chitosan has already been used in various industries, such as biomedical, agriculture, water treatment, cosmetics, textile, photography, chromatography, electronics, paper industry, and food industry. This review article compiles all the essential literature up to the latest developments of chitosan as a potential food packaging material and the outcomes of its practical utilization for this purpose.     

A review: Breathable films for packaging applications

Various packaging technologies have been developed to meet continuously increasing consumer demand for comfortable and safe use, convenience of use, and fresh quality of packaged products. Porous and breathable films provide various advantages such as the minimization of anaerobiosis originating from the accumulation of CO₂ in packaging and the automatic release of steam in a microwave system. Non-porous breathable films are among the alternative candidates for packaging applications and they can respond to desired and undesired temperature fluctuations by reversibly changing the gas permeability depending on the temperature change. They can also prevent problems related to packaging integrity such as the intrusion of insects and microorganisms through perforations, undesired permeation of moisture, and loss of flavor in agricultural products and food. This review mainly addresses porous and non-porous breathable films that are responsive to stimuli like temperature changes. Further, the importance and possible packaging application areas of non-porous breathable films with temperature-dependent gas permeabilities are briefly identified.     

Food applications of active packaging EVOH films containing cyclodextrins for the preferential scavenging of undesirable compounds

Novel ethylene-vinyl alcohol copolymer (EVOH) films containing beta-cyclodextrins (βCD) with potential application in active food packaging have been tested as materials for the preferential retention of undesired food components. The films were immersed on pasteurized milk and UHT milk and stored at 4 and 23 °C, respectively. The films containing βCD presented a significant reduction in cholesterol concentration, achieving a 23% reduction in UHT milk exposed to EVOH films containing 30% βCD. Despite the immobilization of the βCD and the large molecular size of cholesterol, 15% of the βCD molecules added to the films were involved in the formation of βCD/cholesterol inclusion complexes. In another set of experiments, the films were used to reduce the presence of aldehydes (substances which develop as a result of oxidative processes) in packaged fried peanuts. The films containing βCD brought a significant reduction in hexanal, reaching a 50% decrease over short periods (1-5 weeks). At longer storage times (10 weeks) the retention capacity of the developed films was exhausted and no differences were observed between the samples.     

磁性聚乙烯醇微球固定化α-淀粉酶的研究

磁性聚乙烯醇微球为载体,采用戊二醛交联法固定化α-淀粉酶,并对固定化酶的理化性质等进行了研究。结果表明,磁性固定化α-淀粉酶的总活力、蛋白载量、比活、活性回收率分别为1107.89U/g微球、125.36mg/g微球、8.84U/mg蛋白质和37.96%;固定化α-淀粉酶的反应最适温度和最适pH分别为110℃和7.0;固定化α-淀粉酶对金属离子Mg2+、Fe2+、Zn2+和Cu2+的抑制作用的忍耐性比自由酶的明显提高;α-淀粉酶被固定化后其热稳定性、操作稳定性、pH稳定性均比自由酶的明显提高。固定化α-淀粉酶在4℃,pH7.0的缓冲液中保存30d,其活力仍保持最初活力的91.6%,这比其自由酶的高12.3%。     

溶菌酶在羊毛织物上的固定化

以羊毛织物为载体,研究了戊二醛交联固定溶菌酶的工艺条件。结果表明,戊二醛交联工艺的最佳条件为：戊二醛0.2%,交联时间2 h。溶菌酶固定化的条件为：溶菌酶5 g/L,固定化时间6 h,固定化pH值7.0,固定化温度4℃。在此工艺条件下制得的固定化溶菌酶的操作稳定性较好,使用6次后相对酶活仍保持在30%左右。     

Copper-based nanoparticles for biopolymer-based functional films in food packaging applications

This review summarizes the latest developments in the design, fabrication, and application of various Cu-based nanofillers to prepare biopolymer-based functional packaging films, focusing on the effects of inorganic nanoparticles on the optical, mechanical, gas barrier properties, moisture sensitivity, and functional properties of the films. In addition, the potential application of Cu-based nanoparticle-added biopolymer films for fresh food preservation and the effect of nanoparticle migration on food safety were discussed. The incorporation of Cu-based nanoparticles improved the film properties with enhanced functional performance. Cu-based nanoparticles such as copper oxide, copper sulfide, copper ions, and copper alloys affect biopolymer-based films differently. The properties of composite films containing Cu-based nanoparticles depend on the concentration of the filler, the state of dispersion, and the interaction of the nanoparticles with the biopolymer matrix in the film. The composite film filled with Cu-based nanoparticles effectively extended the shelf life by maintaining the quality of various fresh foods and securing safety. However, studies on the migration characteristics and safety of copper-based nanoparticle food packaging films are currently being conducted on plastic-based films such as polyethylene, and research on bio-based films is limited.     

Biodegradable starch/clay nanocomposite films for food packaging applications

Novel biodegradable starch/clay nanocomposite films, to be used as food packaging, were obtained by homogeneously dispersing montmorillonite nanoparticles in different starch-based materials via polymer melt processing techniques. Structural and mechanical characterizations on the nanocomposite films were performed. The results show, in the case of starch/clay material, a good intercalation of the polymeric phase into clay interlayer galleries, together with an increase of mechanical parameters, such as modulus and tensile strength.Finally the conformity of our samples with actual regulations and European directives on biodegradable materials was verified by migration tests and by putting the films into contact with vegetables and simulants.     

Immobilization of humic acid in nanostructured layer-by-layer films for sensing applications

Humic acids (HAs), naturally occurring biomacromolecules, were incorporated into nanostructured polymeric films using the layer-by-layer (LbL) technique, in which HA layers were alternated with layers of poly(allylamine hydrochloride) (PAH). Atomic force microscopy (AFM) revealed very smooth films, with mean roughness varying from 0.89 to 1.19 nm for films containing 5 and 15 PAH/HA bilayers, respectively. The films displayed electroactivity, with the presence of only one reduction peak at ca. 0.675 V (vs Ag/AgCl). Such a well-defined electroactivity allowed the films to be used as highly sensitive pesticide sensors, with detection of pentachlorophenol (PCP) in solutions at concentrations as low as 10(-9) mol L(-1).     

Natamycin release from alginate/pectin films for food packaging applications

Single and composite films based on alginate and pectin containing natamycin as active agent were prepared and the release behavior in water and the diffusion coefficients were evaluated. The influence of natamycin on physical attributes of the films was also investigated. Addition of natamycin promoted an increase in soluble matter in water, in the water vapor permeability and in the opacity and a decreased in tensile strength when compared to films without the added anti-microbial agent. The natamycin mass released by immersion of the film in water fitted well to Fick’s second law diffusional model, with effective diffusivity values ranging from 3.2 × 10⁻⁹ (single pectin films) to 9.2 × 10⁻¹² cm²/s (single alginate films). The values of the diffusional exponents ranged between 0.5 and 1.0, suggesting that the transport process had non-Fickian (anomalous) characteristics. The single alginate films exhibit more suitable attributes for application in packaging than the single pectin and the composite films.     

Incorporation of partially purified hen egg white lysozyme into zein films for antimicrobial food packaging

Lysozyme, partially purified from hen egg white by precipitation of non-enzyme protein with ethanol and lyophilized after dialysis, was incorporated into zein films. The recovery and specific activity of the enzyme after partial purification varied between 45% and 72% and 2173 and 3448 U/mg, whereas the activity of the lyophilized enzyme varied between 2900 and 3351 U/mg. The partially purified enzyme was very stable and lost almost no activity in lyophilized form or in zein films stored at −18 and 4 °C for up to 8 and 4 months, respectively. During partial purification and in zein film preparation, ethanol treatment caused 123–137% and 132–315% activation of the enzyme, respectively. In zein films incorporated with 187–1318 U/cm² (63–455 μg/cm²) lysozyme, the release rates at 4 °C, changed between 7 and 29 U/cm²/min, increased at high lysozyme concentrations. Zein films incorporated with partially purified lysozyme showed antimicrobial effect on Bacillus subtilis and Lactobacillus plantarum. By the addition of disodium EDTA, the films also became effective on Escherichia coli. The results of this study showed that the partially purified lysozyme may be used in antimicrobial packaging to increase food safety.     

Novel natural phenolic compound-based oxygen scavenging system for active packaging applications

An oxygen scavenging system containing a natural phenolic compound, pyrogallol with sodium carbonate, was developed and analyzed as a possible oxygen scavenger. The effect of several parameters, including the amount of pyrogallol and sodium carbonate, relative humidity and storage temperature, on the oxygen scavenging capability were investigated. The initial, glass vial headspace oxygen content (%) of 21.1 % (v/v) decreased to 0.26 % after 8 days of storage at room temperature when the oxygen scavenging system used a 1:1 (w/w) ratio of pyrogallol (250 mg) and sodium carbonate (250 mg). Both pyrogallol and sodium carbonate were required for optimum oxygen scavenging, otherwise the oxygen scavenging ability decreased. The oxygen content (%) decreased further to 6.55 % (v/v) when the amount of sodium carbonate decreased from 250 to 166 mg, which yielded a 2:1 ratio. In the present study, pyrogallol (250 mg) and sodium carbonate (250 mg) had highest oxygen scavenging capacity of 51.81 mL O₂/g and an oxygen scavenging rate of 6.48 mL O₂/g day. The oxygen absorption kinetics rate of pyrogallol and sodium carbonate confirmed that the material has good efficiency for use as an oxygen scavenger. Results indicated that the pyrogallol based oxygen scavenging system with moisture activation can be used as an effective oxygen scavenger for low water activity food packaging applications.     

Antimicrobial nanoparticles and biodegradable polymer composites for active food packaging applications

The food industry faces numerous challenges to assure provision of tasty and convenient food that possesses extended shelf life and shows long-term high-quality preservation. Research and development of antimicrobial materials for food applications have provided active antibacterial packaging technologies that are able to meet these challenges. Furthermore, consumers expect and demand sustainable packaging materials that would reduce environmental problems associated with plastic waste. In this review, we discuss antimicrobial composite materials for active food packaging applications that combine highly efficient antibacterial nanoparticles (i.e., metal, metal oxide, mesoporous silica and graphene-based nanomaterials) with biodegradable and environmentally friendly green polymers (i.e., gelatin, alginate, cellulose, and chitosan) obtained from plants, bacteria, and animals. In addition, innovative syntheses and processing techniques used to obtain active and safe packaging are showcased. Implementation of such green active packaging can significantly reduce the risk of foodborne pathogen outbreaks, improve food safety and quality, and minimize product losses, while reducing waste and maintaining sustainability.     

Mono- and multilayer active films containing lysozyme as antimicrobial agent

Active packaging materials able to release antimicrobial compounds into foodstuff can be used in order to avoid or slow down the bacterial growth during storage. In this work the use of two techniques to control the release of the chosen active compound (lysozyme) from a polymeric material into the foodstuff is proposed: a monolayer cross-linked PVOH film and a multilayer structure made of cross-linked PVOH layers are developed and studied. Lysozyme release tests into water were performed in order to compare the release kinetics from the investigated films. Results suggest that by means of both structures it is possible to control the rate at which lysozyme is released from the PVOH film. The antimicrobial activity of lysozyme released from the investigated films was tested against a suspension of Micrococcus lysodeikticus. Results show that the incorporation of lysozyme into PVOH does not lead to a loss of activity of the enzyme.

Industrial relevance

The increased use of gently processed foods requires packaging to be an integral part of the preservation concept. Consequently additional antimicrobial activity from the packaging material can aid in shelf life extension.This paper concentrates on the release rate of lysozyme, a naturally occuring antimicrobial agent (eg. salvia, mothers milk, raw milk), from multilayer films. A comperision of mono- and multilayer films containing lysozyme regarding their effectiveness on M. lysodeikticus as target organism was also performed. Both aims were met leading to a controlled release of lysozyme with no loss of activity.     

Barrier properties of corn zein nanocomposite coated polypropylene films for food packaging applications

The feasibility of corn zein nanocomposite (CZNC) coatings as an alternative to synthetic polymer barrier layer on polypropylene (PP) films was examined. The effect of layered silicate content in the CZNC layers on the barrier and surface hydrophobicity of the CZNC-PP films were investigated. Incorporation of organomodified montmorillonite (OMMT) by solution intercalation into zein matrix significantly improved oxygen and water vapor barrier of coated PP films. The barrier properties were also investigated theoretically by using various phenomenological permeability models. Tortuous permeation path formed by the fine delamination of nanoclays was found to be responsible for the barrier improvements in zein layers. In conclusion, durable CZNC-PP laminates were developed. CZNC coating of PP films has reduced the oxygen permeability nearly four times, while water vapor permeability reduced by 30% with 5 wt.% OMMT content in 5.9 μm corn zein coating.     

Silk fibroin-based films in food packaging applications: A review

Plastic pollution is a significant concern nowadays due to wastes generated from non-biodegradable and non-renewable synthetic materials. In particular, most plastic food packaging material ends up in landfills, creating mass wastes that clog the drainage system and pollute the ocean. Thus, studies on various biopolymers have been promoted to replace synthetic polymers in food packaging and consequently, the high number of research in biopolymers food packaging, especially in the characterization, properties and also the development of the biopolymer. For biopolymer-based food packaging, silk fibroin (SF) has been highlighted because of its biodegradability and low water vapor permeability properties. This review focuses on the different properties of SF films prepared through solution casting and electrospinning for food packaging. Discussions encompassed chemical properties, mechanical properties, permeability, and biodegradability. This review also discussed the studies that used SF as the biomaterial for food packaging.     

Polyethylene glycol grafted polyethylene: a versatile platform for nonmigratory active packaging applications

Nonmigratory active packaging, in which bioactive components are tethered to the package, offers the potential to reduce the need for additives in food products while maintaining safety and quality. A challenge in developing nonmigratory active packaging materials is the loss of biomolecular activity that can occur when biomolecules are immobilized. In this work, we describe a method in which a biocompatible polymer (polyethylene glycol, PEG) is grafted from the surface of ozone-treated low-density polyethylene (LDPE) resulting in a surface functionalized polyethylene to which a range of amine-terminated bioactive molecules can be immobilized. Free radical graft polymerization is used to graft PEG onto the LDPE surface, followed by immobilization of ethylenediamine onto the PEG tether. Ethylenediamine was used to demonstrate that amine-terminated molecules could be covalently attached to the PEG-grafted film. Changes in surface chemistry and topography were measured by attenuated total reflectance Fourier transform infrared spectroscopy, contact angle, atomic force microscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy. We demonstrate the ability to graft PEG onto the surface of polymer packaging films by free radical graft polymerization, and to covalently link an amine-terminated molecule to the PEG tether, demonstrating that amine-terminated bioactive compounds (such as peptides, enzymes, and some antimicrobials) can be immobilized onto PEG-grafted LDPE in the development of nonmigratory active packaging. PRACTICAL APPLICATION: Nonmigratory active packaging offers the potential for improving food safety and quality while minimizing the migration of the active agent into food. In this paper, we describe a technique to modify polyethylene packaging films such that active agents can be covalently immobilized by a biocompatible tether. Such a technique can be adapted to a number of applications such as antimicrobial, antioxidant, or immobilized enzyme active packaging.     

基于溶胶-凝胶法的羊毛织物溶菌酶固定

 为了增强羊毛织物的抗菌性,采用溶胶-凝胶法将溶菌酶固定在羊毛织物上,以期获得良好的抗菌效果。探讨了溶菌酶固定化的主要工艺,得到最佳工艺条件：丙基三甲氧基硅烷（PTMS）与正硅酸甲酯（TMOS）物质的量比为4：1,水与硅源物质的量比（R值）为32,溶菌酶质量浓度为25mg/mL,稳定剂PVA0588 质量浓度为2mg/mL。羊毛织物固载的溶菌酶具有较好的热稳定性和操作稳定性,40℃下保温100min仍能保持初始酶活的96%,连续使用7次仍能保持初始酶活的52.3%。     

Nanocomposites for food packaging applications

Most materials currently used for food packaging are non-degradable, generating environmental problems. Several biopolymers have been exploited to develop materials for eco-friendly food packaging. However, the use of biopolymers has been limited because of their usually poor mechanical and barrier properties, which may be improved by adding reinforcing compounds (fillers), forming composites. Most reinforced materials present poor matrix–filler interactions, which tend to improve with decreasing filler dimensions. The use of fillers with at least one nanoscale dimension (nanoparticles) produces nanocomposites. Nanoparticles have proportionally larger surface area than their microscale counterparts, which favors the filler–matrix interactions and the performance of the resulting material. Besides nanoreinforcements, nanoparticles can have other functions when added to a polymer, such as antimicrobial activity, enzyme immobilization, biosensing, etc. The main kinds of nanoparticles which have been studied for use in food packaging systems are overviewed, as well as their effects and applications.