Lignocellulosic materials as novel carriers, also at nanoscale, of organic active principles for agri-food applications

Lignocellulosic materials as novel carriers, also at nanoscale, of organic active principles for agri-food applications

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Elena Fortunati and G.M. Balestra Department of Agriculture and Forest Sciences (DAFNE), University of Tuscia, Viterbo, Italy

9.1

Introduction

The emergence of nanotechnology has reached impressive heights in recent years and the development of special nanotools and nanomaterials has found interesting applications in both the agriculture and food sectors. Most of the investigated nanotechnological approaches were initially aimed at solving evolving problems in the agri-food industry in order to enhance their economic potential. Then, after the implementation of new technologies and strategies that used nanostructured materials, the worldwide concern was rapidly extended to numerous applications that could be developed by using the science of materials at the nanoscale [1]. Smart materials, biosensors, packaging materials, nutraceuticals, and nanodevices have been designed to address numerous agri-food-related issues with direct impacts on health, economy, ecology, and industry. As the engineering of nanostructured materials has constantly progressed and extended its applications, their potential is virtually unlimited in this sector. However, the widely differing opinions on the applicability and usefulness of nanotechnology between both specialists and the general public have hampered progress. The main concern manifested by the public is related to the potential risks to health and the environmental impact of the recently developed nanoengineered materials and devices. Therefore, current approaches are strictly considering these concerns when designing nanotechnological solutions for the agriculture and food sectors. In this specific context, the approach to using bio-based and/or biodegradable materials to extract or synthesize nanoscale devices and systems, involving natural sources or wastes as precursors, seems to promise strategies to overcome these safety issues [1]. Lignocellulosic structures, mainly cellulose- and lignin-based nanoscale materials, have recently attracted much attention due to their renewable nature, wide variety of sources available throughout the world, low cost and density, high surface

Biomass, Biopolymer-Based Materials, and Bioenergy. DOI: https://doi.org/10.1016/B978-0-08-102426-3.00009-6 © 2019 Elsevier Ltd. All rights reserved.

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functionality and reactivity. The high mechanical strength, high aspect ratio, and large surface area, allow these nanomaterials to reinforce a wide variety of polymers even at very low filler loadings. Additionally, the nanocomposite approach has been developed as an efficient strategy to increase the structural and functional properties of natural and/or synthetic polymers. The combination of bioresorbable and sustainable polymers with bio-based nanostructures has opened new perspectives in the self-assembly of nanomaterials for different applications with tunable mechanical, thermal, and degradative properties [2]. This chapter addresses the current constant need for inquiries and approaches on the field of agri-food science in order to give an overview about the most recent progress, approaches, and applications that have emerged through nanotechnology, with special focus on the potential of lignocellulosic materials at the nanoscale and their potentialities in both the agriculture, especially in plant pathogen and disease control, and industrial sectors, with a special focus on the food packaging field (Scheme 9.1). Plant-based agricultural production is the basis of the broad agriculture systems providing food, feed, fiber, and fuels. While the demand for crop yields is rapidly increasing, agricultural and natural resources are limited. Modern agricultural practices, associated with the Green Revolution, have greatly increased the global food supply. However, they have had a detrimental impact on the environment, highlighting the need for novel sustainable agricultural methods. It is well documented that excessive and inappropriate use of pesticides has increased toxins in groundwater and surface waters. Moreover, production inputs, including synthetic pesticides, are predicted to be much more expensive due to the constraints of the petroleum reserves. As agriculture is the backbone of most developing countries, nanotechnology has the potential to revolutionize the agri-food sector. It can also guarantee the delivery of drugs, genes, and pesticides to specific sites at cellular

Scheme 9.1 Main goals and focuses of this chapter.

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levels in targeted plants and animals, whilst limiting side effects. Nanotechnology can be used to evaluate gene expression under different stress conditions for both plant and animal foods through the development of nanoarray-based gene technologies. Additionally, this technology can detect fertilizers and pesticides with high precision using smart nanosenors, to enable adequate management of natural resources. Moreover, numerous industrial-related applications with a direct impact on the economy have emerged. For example, nano- and microstructured arrays can detect the early presence of pathogens, contaminants, and food spoilage factors. The broad range of applications in agriculture includes also nanomaterials, possibly bio-based and/or biodegradable, to control crop pests and plant pathogens, which is of interest within this chapter. Over the past decade, patents and products incorporating nanomaterials for agricultural practices (e.g., nanopesticides) have rapidly increased. It has been previously reported that, in 2011, over 3000 patent applications dealing with nanopesticides were submitted [3]. The collective goal of all of these approaches is to enhance the efficiency and sustainability of agricultural practices by requiring less input and generating less waste than conventional products and approaches [4]. Plant diseases are caused by bacteria, fungi, insects, nematodes, phytoplasms, and viruses, and they are responsible for billions of dollars in agricultural crop loss each year in the United States alone (USDA); in addition, over $600 million is spent annually on fungicides in an attempt to control pathogens [5]. In this context, it is very simple to understand the need for novel sustainable and cheap solutions. Other applications in which the nanotechnologies find a great deal of potential applications are smart and active systems for food processing and packaging, as well as nanoemulsion-based decontaminants for food equipment and storage compartments, and nanoparticles that facilitate the bioavailability and delivery of nutrients directly to cells. Most plastic packaging is currently petrochemicalbased and the packaging sector represents about 40% of the annual plastic demand around the world. Many types of commodity and specialty polymers have been used in packaging materials [6,7]; however, conventional plastic packaging also has associated problems of disposal, littering (including ocean pollution), reuse, and recycling, because of the very slow rate of environmental degradation and the lack of collection and recycling infrastructure in many countries. Bio-based polymeric materials are currently considered the only future alternative to petroleumderived polymers, as fossil resources become exhausted. In recent decades, bioplastics have received a lot of interest from the industrial sector, and the civil and scientific community as a valid and strategic alternative to replace the use of traditional plastic based on petroleum. The replacement of traditional plastics by renewable ones is the aim of the modern plastics industry. In this scenario, one of the present societal challenges is to develop biodegradable active materials for food packaging applications in order to improve the shelf-life of food and, at the same time, reduce the environmental impacts associated with synthetic plastics. Biopolymers from different origins can be used for food packaging applications or food-coating purposes, but the functional properties of biopolymer-based materials in terms of their mechanical and barrier properties need to be adapted to

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food requirements. To this end, numerous studies have been carried out applying different strategies to reduce the drawbacks of using biopolymers for packaging purposes. Polar biopolymers, such as starch, chitosan, cellulose derivatives, or proteins, exhibit high water sensitivity and the water plasticization effects lead to a worsening of the mechanical and barrier properties. On the other hand, more hydrophobic matrices, such as biodegradable polyesters, exhibit brittleness and great oxygen permeability, which in turn limit their ability to control the oxidation reactions responsible for food deterioration. Likewise, the incorporation of antimicrobial or/and antioxidant compounds, also embedded into sustainable microand/or nanocarriers, and added to biopolymer-based materials, is a good approach to obtaining active films, with more competitive properties, useful in extending the shelf-life of foodstuffs. The release kinetics of actives into different food systems needs to be evaluated in order to analyze the effectiveness of these materials for food preservation, adapting them to specific target applications, and thus helping to enhance food quality and safety. In this context, the used of nanocarriers could be particularly useful in the modulation of release and the control and maintenance of organoleptic properties of food products. Of the available natural and nontoxic active compounds, essential oils and their major components have been widely studied, due to their antioxidant and antimicrobial properties, together with their “generally recognized as safe” status. The potential benefits of nanotechnology for agriculture, food, fisheries, and aquaculture have been identified and supported by many countries, which have invested a significant amount of money in the development of applications. Also, numerous campaigns are currently trying to increase awareness on the developing process and recent technologies in order to influence the acceptance of customers. Although a nano-agri-food industrialized concept could help to find a sustainable solution for the current global food crisis, the offered advantages should balance the concerns regarding soil, water, environment, and health-related issues that such an approach could bring. In this scenario, this chapter aims to give a general but comprehensive view on recent knowledge regarding the impact of the science of nanometer-sized materials on the agriculture and food industries, also discussing some of the current inquiries regarding advantages in terms of the environment and health, taking into account also safety issues related to nanotechnology applications, aiming at increasing the awareness of a greater number of readers.

9.2

Nanotechnology: special focus on lignocellulosic materials

Nanotechnology is defined, by the US Environmental Protection Agency [8], as the science of matter at dimensions of 1 100 nm. In the agri-food sector, nanoparticles are defined as “particulate based formulations between 10 and 1000 nm in size that are simultaneously colloidal particulate.” The burgeoning applications

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of nanotechnology in the agri-food field will continue to rely on the problemsolving ability of the material and are unlikely to adhere very rigidly to the upper limit of 100 nm. This is because nanotechnology for the agri-food sector should address the large-scale inherent imperfections and complexities of farm productions that might require nanomaterials with flexible dimensions, characteristics, and quantity. However, this is in contrast with the nanomaterial concept that might be working well in well-knit factory-based production systems [9,10]. Nanotechnology design and development are, furthermore, usually represented by two different approaches, top-down and bottom-up. Top-down refers to making nanoscale structures from the smallest structures by machining, templating, and lithographic techniques, whereas the bottom-up approach refers to self-assembly or self-organization at a molecular level, which is applicable in several biological processes [11]. Biologists and chemists are actively engaged in the synthesis of inorganic, organic, hybrid, and metal nanomaterials, including different kinds of nanoparticles that, due to relevant optical, physical, and biological properties, have enormous potential applications in many fields like electronic, medicine, pharmaceuticals, engineering, and agriculture [12]. Lignocellulosic materials are natural, renewable, readily available, environmentally friendly, biodegradable, and inexpensive resources with advantageous characteristics and have significant importance for the industrial sector. In comparison to synthetic materials, some other important advantages in the use of lignocellulosicbased systems and fibers can be envisaged: (1) a wide variety of fillers worldwide extractable from forest and agro sources or wastes; (2) low density, cost, and energy consumption; (3) specific strength and modulus; (4) reactive surfaces that can be easily modified and functionalized by different reactive groups; (5) high applicability in composite and/or nanocomposite systems; and (6) recyclability in comparison with other inorganic fillers [2,13]. Moreover, it is important to stress that lignocellulosic biomass consists of nanoscale building blocks that provide valuable properties to wood and other types of cellulosic and lignocellulosic biomaterials. Typically, most of the lignocellulosic biomass is comprised of about 10 25 wt.% lignin, 20 30 wt.% hemicellulose, and 40 50 wt.% of cellulose [14,15]. Cellulose is the main structural component of plant cell walls, and is responsible for mechanical strength, hemicellulose macromolecules are often repeated polymers of pentoses and hexoses, while lignin usually forms a protective seal around the other two components, that is, cellulose and hemicelluloses. As said earlier, lignocellulosic materials possess great properties that could be useful in material science especially when at the nanoscale (Fig. 9.1A). Cellulose is a fibrous, semicrystalline polymer of high molar mass, carbonneutral, inexpensive raw material that is widely abundant [20]. Its extended chain conformation and microfibrillar morphology contribute to its significant load-carrying capability (Fig. 9.1A) [21]. The possibility of exploiting the high stiffness and strength of cellulose at the nanoscale (nanocellulose), with its remarkable physical properties, special surface chemistry, and excellent biological properties, has opened the possibility of its use in the production of highperformance nanosystems and nanodevices. Nanocellulose exists in a number of

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Figure 9.1 (A) Cellulosic fiber structure [16]; (B) transmission electron images of MFC from potato pulp (a) [17], CNC from microcrystalline cellulose (b) [18], and scanning electron image of BC (c) [19]. Source: Reprinted with permission from Fortunati E, Yang W, Luzi F, Kenny J, Torre L, Puglia D. Lignocellulosic nanostructures as reinforcement in extruded and solvent casted polymeric nanocomposites: an overview. Europ Polym J 2016;80:295 316.

forms, fibrillated cellulose (homogenized cellulose pulps), nanocrystalline cellulose/cellulose nanocrystals or whiskers (acid hydrolyzed), and bacterial cellulose; all these different cellulosic structures have found applications in drinking water filtration, catalytic degradation of organic pollutants, absorbents for the removal of oil from water, censoring of organic contaminants and waterborne pathogens, and as energy-conversion devices [22]. Specifically, the nanosized cellulosic particles were classified on the basis of preparation methods as microfibrillated cellulose (MFC) or nanofibrillated (NFC), nanocrystalline cellulose/cellulose nanocrystals (CNC), also called cellulose nanowhiskers and bacterial cellulose

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(BC), that is, another nanosized biomaterial biosynthesized through microorganisms (Fig. 9.1B). MFC, CNC, and BC represent different nanocellulose structures extracted by applying different procedures, and showing dissimilar dimensions. Cellulose microfibrils (Fig. 9.1Ba), which are also called nanofibrillated cellulose, can be extracted, by means of a mechanical disintegration process, from various natural sources. MFC is composed of long, flexible, and entangled cellulose nanofibers, containing both amorphous and crystalline domains and is characterized by high specific area, high aspect ratio, and high ability to establish hydrogen bonding. The delamination of cellulose resources is a procedure characterized by intense mechanical treatments and, sometimes, depending on the wood material source, a pretreatment able to facilitate the mechanical one is required [2]. In the 1950s, Ranby obtained, for the first time, by controlled sulfuric acid hydrolysis, a colloidal suspension of cellulose [23]. Cellulose nanocrystals are rigid rod-like particles with a typical acicular structure (Fig. 9.1Bb), monocrystalline domains of 1 100 nm in diameter and 100 to hundreds of nanometers in length [22]. The morphology and the crystallinity degree of CNC depend on the natural sources utilized as raw material, preparation conditions, and also on the different parameters adopted during the extraction process. The extraction of CNC from different natural cellulosic materials occurs in two stages. The first is a pretreatment characterized by complete or partial removal of hemicelluloses, lignin, waxes, and holocellulose, while the second is a controlled chemical or enzymatic treatment (or hydrolysis) able to both remove the amorphous regions and extract cellulose nanostructures with high crystallinity [22]. In the last few years, some authors have also focused their attention on the surface modifications of CNC (due to the presence and abundance of hydroxyl groups on their surfaces), in particular some functionalizations have been considered, including etherification, oxidation, esterification, polymer grafting, silylation, etc. Several chemical functionalizations have been investigated to obtain better dispersion, introducing stable negative or positive electrostatic charges on the nanocellulose surface (CNC extracted by sulfuric acid hydrolysis introduced on the nanocellulosic materials labile sulfate moieties that are readily removed under mild alkaline conditions). Concerning their final properties, cellulose nanocrystals have some different interesting properties: CNCs have high stiffness, low density (approximately 1.57 g/cm3), very low thermal expansion coefficient (estimated to be about 1027 K21) [24], high elastic modulus around 150 GPa [25]: all these interesting characteristics permit CNC to be used as the reinforcement phase in thermoplastic and/or thermosetting matrices for many different applications. Moreover, they can be used in the biomedicine, pharmaceutical, and agricultural sectors for the release of specific drugs and/or active substances. In 1886, Brown observed for the first time that strains of Acetobacter bacteria produced a white gelatinous pellicle on the surface of a liquid medium, which was chemically equivalent to cell-wall cellulose [26,27]. The produced material, bacterial cellulose (BC), also called bacterial nanocellulose (BNC), microbial cellulose, or biocellulose, is formed by aerobic bacteria, such as acetic acid bacteria of the genus Gluconacetobacter xylinum. BC has a high weight-average molecular weight

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(Mw), high crystallinity, and good mechanical stability. This highly crystalline structure of BC and high Young’s modulus values are favorable properties for composite production. Due to its good mechanical properties, biocompatibility, water sorption capacity, porosity, stability, and conformability, BC was investigated for possible use in many different sectors, such as tissue engineering of cartilage, replacement of blood vessels in rats, the wound healing process, and in packaging applications that are in contact with foods [2]. Lignin is the second most abundant natural aromatic polymer on Earth. As a natural material with great chemical and physical properties (Fig. 9.2), obtainable at an affordable cost, lignin substitution potential extends to any product currently sourced from petrochemical substances. In recent years, different lignin nanoparticles, from various resources, have been synthesized by different chemical/physical approaches. The areas in which lignin is applicable include emulsifiers, dyes, synthetic floorings, sequestering, binding, dispersal agents, and paints. In addition, all currently important industrial organic chemicals such as hydrocarbons, alcohols, polyols, ketones, acids, and phenol derivatives can be obtained by chemical processing of wood [28]. In detail, new potential lignin applications include (1) lignin valorization for biofuels and energy production, (2) lignin exploitation toward high-molecular-mass applications like polymers (e.g., polyurethane foams), wood adhesives, and carbon fibers, and (3) lignin utilization for the production of polymer building blocks, aromatic monomers including benzene, toluene, and xylene, phenol, and vanillin. Moreover, very recently, the lignin-based polymer composites have attracted the interest of the research community all over the world and intense efforts have been made to use lignin as a low-cost eco-friendly reinforcement to prepare high-

Figure 9.2 Appearance and chemical structures of lignin. Source: Reprinted with permission from Fortunati E, Yang W, Luzi F, Kenny J, Torre L, Puglia D. Lignocellulosic nanostructures as reinforcement in extruded and solvent casted polymeric nanocomposites: an overview. Europ Polym J 2016;80:295 316.

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performance composites. Finally, the free radical scavenging (FRS) activity of lignin and especially lignin nanoparticles were recently studied, opening perspective application in many fields as well as in the agri-food sector due to their interesting active characteristics. Ge et al. [29] investigated the FRS activity of nanoscaled lignin prepared by a solution-precipitation method with either ethylene glycol or alkaline solution, and the results indicated that alkaline solution methods give smaller average particle size (278 6 13 nm) than ethylene glycol (375 6 18 nm). They found that the nanoscaled lignin obtained by alkaline solution precipitation exhibited 3.33-fold higher FRS activity than the other one, because of the smaller particle size. Since a higher surface area will result in higher solubility and bioavailability, the experimental results confirmed that the nanoscaled lignin had dissolution of approximately 31% and it took less than 2 hours to reach equilibrium, while nonnanoscaled lignin had dissolution of 2.5% and took 4 hours to reach equilibrium. 2,2-Diphenyl-1-picrylhydrazyl (DPPH) antioxidant assay results showed that nanoscaled lignin also had higher antioxidant activity. The antioxidant effect has been also studied by Domenek et al., who investigated, in the field of material applications, the antioxidant activity of micro-scaled lignin as a natural substitute of synthetic antioxidants for the protection of the food, opening the door to the fabrication of active packaging materials compounded with natural antioxidant substances [30]. Lignin seems to be also a promising green agent useful against dangerous microorganisms. A recent example is the introduction of lignin core into silver nanoparticles. Although silver nanoparticles could target a broad spectrum of microorganisms including but not limited to Escherichia coli and Pseudomonas aeruginosa, they also have disadvantages. In their activated form, the unused silver nanoparticles remain in the environment and could adversely affect ecosystems. Richter et al. [31] hypothesized that lignin, which is in abundance and environmentally friendly, could be used to replace the silver core. They tested the environmentally benign lignin-core nanoparticles against various strains of bacteria to evaluate their antimicrobial efficiency. Surprisingly, the lignin nanoparticles outperformed the controls, silver nitrate solution, and conventional silver nanoparticles, which had 12 times and 20 times more silver ions, respectively. In addition, it was found that the potency against microorganisms was lost when the silver ions were completely utilized.

9.3

Plant protection sector

Many plant pathogens (i.e., bacteria, fungi) attack crops and vegetable/fruits in storage and seriously threaten worldwide production of important vegetables. Besides yield reductions, fruit lesions disfigure and reduce the marketability of both fresh-market and processed fruits. Pesticides are a crucial input in agriculture, and are used to control plant pests and plant pathogens and to secure quality and yield in plant production. At the same time, concerns are mounting over the effects of plant protection products on the environment, nontarget organisms, and

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human health. Consumers and the food chain alike are increasingly demanding food products that are residue-low or residue-free and produced in more sustainable ways. This applies particularly to fruit and vegetables, which are often consumed fresh without prior processing. Worldwide policies seek to reduce reliance on pesticides for crop protection through the design and implementation of more integrated approaches and restrictions on the use of several active substances currently used in pesticides. The worldwide consumption of pesticides is about two million tons per year: of which 45% is used in Europe alone, 25% is consumed in the USA, and the remainder shared around the world [32]. The increased parasite resistance to pesticides asks for the development of alternatives and sustainable approaches against relevant biotic agents of disease developing much greener pesticides in respect to those actually utilized. The diffusion and the huge use over time of conventional plant protection strategies is leading to degradation of natural ecosystems, highlighting over the last years the need for more sustainable agricultural techniques. A promising alternative to traditional methods could be to apply nanotechnologies in the agriculture sector: this opens many possibilities, covering the entire productive thread/chain, from seed to final products. In plant protection field, as a definition, nanopesticides “involve either very small particles of pesticidal active ingredients or other small engineered structures with useful pesticidal properties,” showing a large number of advantageous properties such as thermal stability, solubility, biodegradability, and permeability; moreover, nanoemulsions, nanoencapsulates, nanocontainers, and nanocages may be a good instrument for nanopesticide delivery to a specific site [33]. In this context, nanotechnology can change the entire scenario through the development of new tools able to minimize production inputs and maximize agricultural production outputs, thus meeting the increasing need for global sustainability [11]. Nanostructured materials can offer great opportunities of application in the agricultural field although, until now, their use in this specific sector, and especially in plant protection, has been poorly explored [34,35]. For example, on plant pathogens (bacteria and fungi) of cucumber it was demonstrated that treatment with TiO2 nanoparticles determines a remarkable reduction of infection by Pseudomonas syringae pv. lachrymans and Pseudoperonospora cubensis, and also increasing photosynthetic activity [36]. In grape, nanoformulations were useful inside xylem vessels to counter bacterial colonization [37] and demonstrated potential antimicrobial activity against the bacterium Xylella fastidiosa [38]. In respect to fungal plant pathogens, a great potential role of nanoformulations based on ZnO and MgO nanoparticles was noted against Alternaria alternata, Fusarium oxysporum, Rhizopus stolonifer, and Mucor plumbeus [39]; similarly, Giannousi et al. tested the antifungal activity of cupper-based nanoparticles (Cu2O) toward Phytophthora infestans on tomato and reported that foliar application resulted in a significantly greater protection (73.5%) from the pathogen, compared to currently available non-nano Cu formulations (57.8%) [40]. Nanoformulations, especially if developed with natural-based materials, and applied in plant protection activities, could be particularly beneficial as biopesticides since they could be safer for plants and cause less environmental pollution in comparison to

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conventional chemical pesticides [41]; moreover, if they are employed as nanosized aqueous dispersion formulations it was suggested that they enhance the bioavailability of pesticides [42].

9.4

Food protection: food active packaging

The advent of nanotechnology has opened up opportunities for the development of new packaging materials with improved properties for use as food contact materials. There has been an increasing trend in recent years in R&D into the development of packaging materials based on nanomaterial polymer composites: the incorporation of nanomaterials into polymers has been reported to improve mechanical and/or barrier properties, which is of great interest for applications in food packaging. As the uses of nanotechnology have progressed, it has been found to be a promising technology for the food packaging industry in the global market: such new packaging materials have excellent barrier properties to prevent the migration of oxygen, carbon dioxide, water vapor, and flavor compounds, higher surface-tovolume ratio than their microscale counterparts, and, therefore, they are able to attach to a vast number of biological molecules, which enhances their efficiency [43]. Some conventional fillers and additives, at the nanoscale, are generally sufficient to improve the properties of packaging materials without any significant changes in density, transparency, and processing characteristics [44]. The addition of nanoparticles into shaped objects (e.g., bottles, containers), and other forms of packaging (e.g., films) can render them light, fire-resistant, and stronger in terms of mechanical and thermal performance, and may also make them less permeable to gases. A number of the world’s largest food companies have been reported to be actively exploring the potential of nanotechnologies for use in food and food packaging. In this specific framework, nanocomposites based on thermoplastic polymers, and especially biopolymers, may serve as a significant route for the development of new and innovative food packaging materials by extending the shelf-life and improving the food quality, while minimizing environmental pollution after usage. Key driving factors identified in the bio-based biodegradable plastics market are a regulatory framework for safe waste disposal and management, implementation of environmental conservation initiatives by governments and various institutions, and efforts from manufacturers to reduce dependency on crude oilderived products. Nanotechnology is expected to change the entire packaging industry, with self-assembly reducing fabrication costs and infrastructure, and more flexible packaging methods providing consumers with fresher and more customized products. Nanotechnology will be an enabler to deliver smart, novel packaging that can benefit not only the producer, but also the consumer, by providing extended shelf-life with additional product information and enhanced security at a cost that is acceptable both to the producer and the consumer. Nanotechnology is exciting and is already being used extensively in packaging, and the future nano-enabled packaging developments are expected to include not only nanocomposites containing nanoclays to improve the

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strength and flexibility of packing materials, but also nanosensors in packaging systems to detect pathogens and contaminants, and packages with tracking nanocomponents to help producers monitor products as they move through the supply chain. However, even if concerns have been expressed about the inclusion of nanomaterials and the potential for free nanomaterials getting into the environment, nanotechnology will lead to enhanced performance for lower total packaging weights, and there is likely to be less waste for disposal. Nevertheless, the actual use of polymer nanocomposites in industry is going very slowly, and the main reasons are represented by the cost of materials and processing, restrictions due to legislation, acceptance by customers in the market, lack of knowledge about the effectiveness and impact of nanoparticles on the environment and on human health, the potential risk due to migration of nanoparticles into food, and the balance between the use of biomass to produce materials or food. For these reasons, the use of sustainable, natural, cheap, and secure materials as lignocellulosic systems, at the nanoscale, represents an important alternative solution able also to overcome the safety issues. Moreover, during the last decade, many studies have been carried out on the use of sustainable materials, as biopolymers or lignocellulosic-based systems as carriers of active ingredients, essential oils (EO), and their main compounds, with the aim of responding to consumer demand for preservative-free, safer products. Thus, different carbohydrate polymers, such as chitosan, cellulose derivatives, alginates, gelatine, etc., have been used both to incorporate EO and to develop film formulations for the purposes of improving food quality and extending its shelf-life. Different plant and animal proteins, such as gelatine, whey, soy, and milk proteins, have also been extensively used. Among the most effective compounds/EOs that may be found are carvacrol, thymol, cinnamaldehyde or oregano, cinnamon, and clove EOs, attaining the total microbial inhibition of several foodborne pathogens. Despite the remarkable antimicrobial activity of the EO against most foodborne pathogens in in vitro tests, several authors have reported that higher amounts are required to achieve similar results on real foodstuffs. This can be explained by the interactions of some food ingredients with the EO compounds, which sequester them, thereby limiting their antimicrobial activity. Other compounds, such as enzymes, proteins, peptides, etc. could be used as active agents in packaging formulations. Nisin release, for example, from cellulose structures into packaging films was evaluated by Grower et al. [45]. The release of active agent from cellulose showed noninhibition of Listeria monocytogenes strains due to some assay conditions such as pH and the amount of the substance released and retained. The nisin inhibited bacterial growth only at the 8th day due to pH neutralization and the period of nisin release [45]. Furthermore, not only active molecules could be considered as active agents in polymeric systems for food packaging applications, but also polymeric nanoparticles can be used as fillers to produce nanocomposites suitable for food packaging [46]. Accordingly, chitosan/sodium tripolyphosphate (TPP) nanoparticles were incorporated into hydroxyproplymethyl-cellulose (HPMC) films for food packaging [47]. The mechanical properties of the films were significantly enhanced by the addition of chitosan nanoparticles, due to the ability of the polymeric nanoparticles

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to fill discontinuities in the HPMC matrix. Moreover, inorganic nanoparticles could be combined with lignocellulosic materials in food packaging solutions. Silver nanoparticles, for example, were prepared and incorporated into carboxymethyl cellulose films for food packaging applications. The antimicrobial activity of silver nanoparticles was prepared by the casting method, and it was found that the silver nanoparticles inhibited the growth of the microorganisms tested. The carboxymethyl cellulose film embedded with silver nanoparticles showed the best antimicrobial effect against Gram-positive (Enterococcus faecalis) and Gram-negative (E. coli) bacteria (0.1 µg/mL) [48]. Cellulosic-based materials are also used as templates to synthesize inorganic particles, as copper nanoparticles [49 51], and then embedded in different polymers for many different applications. Zhong et al. [49], for example, proved antimicrobial efficiency after the incorporation of carboxymethyl cellulose-copper nanoparticles into poly(vinyl alcohol) (PVA) thermoplastic polymer largely used in biomedical and pharmaceutical sectors as well as in the packaging field. They demonstrated that the incorporation of carboxymethyl cellulose-copper nanoparticles at 0.6% in the PVA composite film resulted in a significant increase in microbial reduction when compared to lower levels of filler [49].

9.5

Recent contribution on plant and food protection

To address a green and particularly sustainable approach for nanostructured materials useful for biopesticide development, it is fundamental to select, characterize, and deeply evaluate the possibility to use bio-based and/or natural molecules, materials, and active ingredients (AIs) able to contrast and inhibit the development of plant parasites. In this scenario, the use of natural compounds for the biocontrol of different plant pathogens represents an alternative, particularly, attractive for the future mostly in consideration of the many concerns about traditional pesticides to support crop cultivation/food production [52 55]. Vegetal extracts of Allium sativum and of Ficus carica showed a relevant antibacterial activity to protect tomato plants against Xanthomonas axonopodis pv. vesicatoria and Clavibacter michiganensis subsp. michiganensis bacterial quarantine plant pathogens [56]. Moreover, with respect to the causal agent of tomato bacterial speck, antibacterial activity using Punica granatum fruit peel extract was evident in in vivo trials and effective for at least 15 days, offering the possibility of replacing, reducing, or even alternating treatments involving copper compounds [57]. Remarkable results were obtained by using organic cellulose based microparticles containing gallic and ellagic acids to control different bacterial plant pathogens on kiwi fruit plants [58] and the original results were recently obtained by using 50% less cupric salts in association with AIs in order to control the causal agent of tomato bacterial spot disease [59] (Fig. 9.3). Concerning microparticle approaches in plant protection, cellulosic microparticles loaded with gallic acid were able to significantly reduce the bacterial speck epiphytic population, showing an activity comparable to that obtained by

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Figure 9.3 Magnification (25,000 3 ) of cupric salt and AI formulation (A); light bacterial spot symptoms on tomato leaf caused by X. axonopodis pv. vesicatoria (Xav) 2 weeks after distribution of formulation (B); related record (10,000 3 ) of Xav cells on tomato leaves.

copper salts against tomato plant pathogens. Biocompatible spray-dried organic microparticles allowed the formulation of innovative products useful to reduce phytotoxicity and risk of copper resistance in plant pathogens associated with the frequent agricultural use of cupric compounds [60]. Moreover, Fortunati et al. [61] pointed out the potentiality of organic carriers, at the nanoscale, against the bacterial plant pathogen P. syringae pv. Tomato (Pst), the causal agent of bacterial speck. Specifically, novel poly(DL-lactide-co-glycolide acid) (PLGA) copolymer-based biopolymeric nanoparticles (NP) and cellulose nanocrystals (CNC) were evaluated as basic materials for use as nanocarriers to develop innovative plant protection formulations. PLGA NPs were synthesized and tested, and the effect of natural surfactants, such as starch and CNC, on the NP final properties was investigated. Moreover, CNC were evaluated as a possible nanostructured formulation to be directly applied in plant protection. The results underlined that the proposed novel carriers could be employed without any detrimental effect on tomato plant development. The proposed nanocarriers are, in fact, able to cover, with an uniform distribution, the tomato vegetal surfaces without any damage and to allow regular development of the tomato-treated plants. Moreover, starch PLGA NP formulations were unsuitable for Pst survival and multiplication on the tomato plant surfaces. A great potentiality comes up of these nanocarriers on plants to carry out and release antimicrobial active ingredients useful in innovative and sustainable plant protection strategies [61] (Fig. 9.4).

9.6

Conclusions and future trends

The agricultural sector is facing pivotal global challenges, such as climate change, urbanization, sustainable use of resources, and environmental issues. These situations are further exacerbated by the growing demand for food that will be needed to sustain an estimated population growth from the current level of about 6 billion to 9 billion by 2050. Nanotechnology has the potential to conceive products based on environmentally friendly natural polymers like lignocellulosic materials which in addition to being biodegradable can also be obtained from natural biowaste [3,62]. The hope is to develop new nanopesticides taking into account all the properties of organic carriers and associated active ingredients with biocidal activity. A “green”

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Figure 9.4 Observation of CNC suspension (A), on the adaxial (B) and diaxial (C) sides of tomato leaves by FESEM. Source: Reprinted with permission from Fortunati E, Rescignano N, Botticella E, Lafiandra D, Renzi M, Mazzaglia A, et al. Effect of poly (DL-lactide-co-glycolide) nanoparticles or cellulose nanocrystals-based formulations on Pseudomonas syringae pv. tomato (Pst) and tomato plant development. J Plant Dis Prot 2016;123(6):301 310.

technological platform applicable to crops and fresh agri-food productions able to combat plant and food pests without chemicals could be the main goal in the near future. A very attractive feature is that nanoscaled formulations, increasing dispersivity and degradability of a pesticide in soil and their effectiveness inside the plant, whilst dispensing natural active substances into nanoencapsulated formulations, will allow an optimal solution for sustainable plant protection strategies. Nanostructured formulations for plant and food protection will allow for a significant reduction of chemicals, consequently reducing the costs of crops and food production. Their advantages should be tangible in terms of greater efficacy and persistence, reduction of toxicity, greater selectivity for crops and fresh food, improved adhesion to treated surfaces, preservation of food quality, reduction of residues in the final product, and protection of the environment and consumers.

References [1] Grumezescu AM. Food preservation nanotechnology in the agri-food industry. vol. 6. Elsevier; 2017. [2] Fortunati E, Yang W, Luzi F, Kenny J, Torre L, Puglia D. Lignocellulosic nanostructures as reinforcement in extruded and solvent casted polymeric nanocomposites: an overview. Europ Polym J 2016;80:295 316. [3] Kah M, Beulke S, Tiede K, Hofmann T. Nanopesticides: state of knowledge, environmental fate, and exposure modeling. Crit Rev Enciron Sci Technol 2013;43 (16):1823 67. [4] Chinnamuthu CR, Boopathi PM. Nanotechnology and agroecosystem. Madras Agric J 2009;96:17 31. [5] Gonzalez-Fernandez R, Prats E, Jorrin-Novo JV. Proteomics of plant pathogenic fungi. J Biomed Biotechnol 2010;2010:932527. [6] Hernandez RJ, Selke SEM, Culter JD. Major plastics in packaging. Plastics packaging: properties, processing, applications and regulations, 89. Brooks: Carl Hanser Verlag; 2000. p. 303 4.

176

Biomass, Biopolymer-Based Materials, and Bioenergy

[7] Giles GA, Bain DR. Types of plastics materials, barrier properties and applications. Materials and development of plastics packaging for the consumer market, 2. Sheffield Academic Press; 2000. p. 16 45. [8] U.S. EPA Nanotechnology White Paper; 2007. [9] Fortunati E, Verma D, Luzi F, Mazzaglia A, Torre L, Balestra GM. Novel nanoscaled materials from lignocellulosic sources: potential applications in the agricultural sector. Handbook of Ecomaterial Springer; 2017. [10] Mazzaglia A, Fortunati E, Kenny JM, Torre L, Balestra GM. Nanomaterials in Plant Protection in: Nanotechnology in Agriculture and Food Science. M.A.V. Axelos and M. van De Voorde, Wiley-VCH GmbH $& Co. 7:408. pp. 115 133. [11] Mukhopadhyay SS. Nanotechnology in agriculture: prospects and constraints. Nanotechnol Sci Appl 2014;7(2):63 71. [12] Salata O. Applications of nanoparticles in biology and medicine. J Nanobiotechnol 2004;. [13] Mohanty AK, Misra M, Drzal L. Sustainable bio-composites from renewable resources: opportunities and challenges in the green materials world. J Polym Environ 2002;10:19 26. [14] Iqbal KMN, Ahmed I, Zia MA, Irfan M. Purification and characterization of the kinetic parameters of cellulose produced from wheat straw by Trichoderma viride under SSF and its detergent compatibility. Adv Biosci Biotechnol 2011;2:149 56. [15] Kumar P, Barrett DM, Delwiche MJ, Stroeve P. Methods for pretreatment of lignocellulosic biomass for efficient hydrolysis and biofuel production. Ind Eng Chem Res 2009;48:3713 29. [16] Lavoine N, Desloges I, Dufresne A, Bras J. Microfibrillated cellulose its barrier properties and applications in cellulosic materials: a review. Carbohyd Polym 2012;90:735 64. [17] Dufresne A, Dupeyre D, Vignon MR. Cellulose microfibrils from potato tuber cells: processing and characterization of starch-cellulose microfibril composites. J Appl Polym Sci 2000;76:2080 92. [18] Fortunati E, Armentano I, Zhou Q, Iannoni A, Saino E, Visai L, et al. Multifunctional bionanocomposite films of poly (lactic acid), cellulose nanocrystals and silver nanoparticles. Carbohyd Polym 2012;87:1596 605. [19] Ul-islam M, Khan T, Park JK. Nanoreinforced bacterial cellulose-montmorillonite composites for biomedical applications. Carbohyd Polym 2012;89:1189 97. [20] Klemm D, Kramer F, Moritz S, Lindstrom T, Ankerfors M, Gray D, et al. Nanocellulose: a new family of nature-based materials. Angew Chem 2011;50:5438 66. [21] Berglund L. Cellulose-based nanocomposites. Natural fibers, biopolymers and biocomposites. CRC Press; 2005. [22] Brinchi L, Cotana F, Fortunati E, Kenny JM. Production of nanocrystalline cellulose from lignocellulosic biomass: technology and applications. Carbohyd Polym 2013;94:154 69. ¨ ber den feinbau der zellulose Experimentia. 1950;6:12 14. [23] Ranby BG, Ribi E. U [24] Nishino T, Matsuda I, Hirao K. All-cellulose composite. Macromolecules 2004;37:7683 7. ˇ ´ A, Davies GR, Eichhorn SJ. Elastic modulus and stress-transfer properties of [25] Sturcova tunicate cellulose whiskers. Biomacromolecules 2005;6:1055 61. [26] Brown AJ. XLIII.d on an acetic ferment which forms cellulose. J Chem Soc Trans 1886;49:432 9. [27] Brown AJ. XIX.d the chemical action of pure cultivations of bacterium aceti. J Chem Soc Trans 1886;49:172 87.

Lignocellulosic materials as novel carriers

177

[28] Hatakeyama H, Hatakeyama T. Lignin structure, properties, and applications in biopolymers-lignin, proteins, bioactive nanocomposites. In: Abe A, Dusek K, Kobayashi S, editors. Advances in polymer science. Springer Berlin Heidelberg; 2010. [29] Ge Y, Wei Q, Li Z. Preparation and evaluation of the free radical scavenging activities of nanoscale lignin biomaterials. BioResources. 2014;9:6699 706. [30] Domenek S, Louaifi A, Guinault A, Baumberger S. Potential of lignins as antioxidant additive in active biodegradable packaging materials. J Polym Environ 2013;21:692 701. [31] Richter AP, Brown JS, Bharti B, Wang A, Gangwal S, Houck K, et al. An environmentally benign antimicrobial nanoparticle based on a silver-infused lignin core. Nature Nanotechnol 2015;10:817 23. [32] De A, Bose R, Kumar A, Mozumdar S. Targeted delivery of pesticides using biodegradable polymeric nanoparticles. Springer; 2014. [33] Bergeson LL, MacDougall LS, Navin-Jones M. Turkey Enacts REACH-like Chemical Program: what Stakeholders Need to Know, Chemical Regulation Reporter, International Issues Turkey, Bureau of National Affairs; 2010. [34] Rai M, Ingle A. Role of nanotechnology in agriculture with special reference to management of insect pests. Appl Microbiol Biotech 2012;94:287 93. [35] Khot LR, Sankaran S, Maja JM, Ehsani R, Schuster EW. Applications of nanomaterials in agricultural production and crop protection: a review. Crop Prot 2012;35:64 70. [36] Cui H, Zhang P, Gu W. Application of anatase TiO2 sol derived from peroxotitannic acid in crop plant diseases control and growth regulation. Nanotechnology Conference and Expo 2009 (abstr.) 2009; 3–7 May, Houston TX. [37] Zaini PA, De La Fuente L, Hoch HC, Burr TJ. Grapevine xylem sap enhances biofilm development by Xylella fastidiosa. FEMS Microbiol Lett 2009;295(1):129 34. [38] Herna´ndez-Montelongo J, Nascimento VF, Murillo D, et al. Nanofilms of hyaluronan/ chitosan assembled layer-by-layer: an antibacterial surface for Xylella fastidiosa. Carbohydr Polym 2016;136:1 11. [39] Wani AH, Shah MA. A unique and profound effect of MgO and ZnO nanoparticles on some plant pathogenic fungi. J Appl Pharm Sci 2012;2:40 4. [40] Giannousi K, Avramidis I, Dendrinou-Samara C. Synthesis, characterization and evaluation of copper based nanoparticles as agrochemicals against. Phytophthora infestans. RSC Adv 2013;3:21743 52. [41] Mohanpuria P, Rana NK, Yadav SK. Biosynthesis of nanoparticles: technological concepts and future applications. J Nanopar Res 2008;10:507 17. [42] Strom RM, Price CD, Lubetkin SD. Aqueous dispersions of agricultural chemicals, US Patent; 2001. [43] Honarvar Z, Hadian Z, Mashayekh M. Nanocomposites in food packaging applications and their risk assessment for health. Electr Phys 2016;8(6):2531 8. [44] Lei SG, Hoa SV, Ton-That MT. Effect of clay types on the processing and properties of polypropylene nanocomposites. Compos Sci Technol 2006;66:1274 9. [45] Grower JL, Cooksey K, Getty K. Release of nisin from methylcellulosehydroxypropyl methylcellulose film formed on low-density polyethylene film. J Food Sci 2005;69:107 11. [46] De Azeredo HM. Nanocomposites for food packaging applications. Food Res Int 2009;42(9):240 1253. [47] De Moura MR, Aouada FA, Avena-Bustillos RJ, McHugh TH, Krochta JM, Mattoso LHC. Improved barrier and mechanical properties of novel hydroxypropyl methylcellulose edible films with chitosan/tripolyphosphate nanoparticlses. J Food Eng 2009;92:448 53.

178

Biomass, Biopolymer-Based Materials, and Bioenergy

[48] Siqueira MC, Coelho GF, Moura MR, Bresolin JD, Hubinger SZ, Marconcini JM, et al. Evaluation of antimicrobial activity of silver nanoparticles for carboxymethylcellulose film applications in food packaging. J Nanosci Nanotechnol 2014;14:5512 17. [49] Zhong T, Oporto GS, Jaczynski J, Jiang C. Nanofibrillated cellulose and copper nanoparticles embedded in polyvinyl alcohol films for antimicrobial applications. BioMed Res Int 2015;1 8. [50] Zhong T, Oporto GS, Jaczynski J, Tesfai AT, Armstrong J. Antimicrobial properties of the hybrid copper nanoparticles-carboxymethyl cellulose. Wood Fiber Sci 2013;45 (2):215 22. [51] Zhong T, Oporto GS, Peng Y, Xie X, Gardner DJ. Drying cellulosebased materials containing copper nanoparticles. Cellulose 2015;22:2665 81. [52] Copping LG, Menn JJ. Review biopesticides: a review of their action, applications and efficacy. Pest Man Sci 2000;56:651 76. [53] Gahukar R. Evaluation of plant-derived products against pests and diseases of medicinal plants: a review. Crop Prot 2012;42:202 9. [54] Lo Cantore P, Iacobellis NS, De Marco A, Capasso F, Senatore F. Antibacterial activity of Coriandrum sativum L. and Foeniculum vulgare Miller var. vulgare (Miller) essential oils. J Agr Food Chem 2004;52:7862 6. [55] Pradhanang P, Momol M, Olson S, Jones J. Effects of plant essential oils on Ralstonia solanacearum population density and bacterial wilt incidence in tomato. Plant Dis 2003;87:423 7. [56] Balestra GM, Heydari A, Ceccarelli D, Ovidi E, Quattrucci A. Antibacterial effect of Allium sativum and Ficus carica extracts on tomato bacterial pathogens. Crop Prot 2009;28:807 11. [57] Quattrucci A, Ovidi E, Tiezzi A, Vinciguerra V, Balestra GM. Biological control of tomato bacterial speck using Punica granatum fruit peel extract. Crop Prot 2013;46:18 22. [58] Rossetti A, Mazzaglia A, Muganu M, Paolocci M, Sguizzato M, Esposito E, et al. Microparticles containing gallic and ellagic acids for the biological control of bacterial diseases of kiwifruit plants. J Plants Dis Prot 2017;97:472. [59] Giovanale G, Fotunati E, Mazzaglia A, Balestra GM. Possibilities of copper reduction in control of tomato bacterial disease. J Plant Pathol 2017;99:27. [60] Cortesi R, Quattrucci A, Esposito E, Mazzaglia A, Balestra GM. Natural antimicrobials in spray-dried microparticles based on cellulose derivates as potential eco-compatible agrochemicals. J Plant Dis Prot 2016;124(3):268 9. [61] Fortunati E, Rescignano N, Botticella E, Lafiandra D, Renzi M, Mazzaglia A, et al. Effect of poly (DL-lactide-co-glycolide) nanoparticles or cellulose nanocrystals-based formulations on Pseudomonas syringae pv. tomato (Pst) and tomato plant development. J Plant Dis Prot 2016;123(6):301 10. [62] Gogos A, Knauer K, Bucheli TD. Nanomaterials in plant protection and fertilization: current state, foreseen applications, and research priorities. J Agric Food Chem 2012;60 (39):9781 92.