REVIEW Ital. J. Food Sci., vol. 27 - 2015 1 - Keywords: biodegradable packaging, biopolymers, edible coating, fresh-cut fruits and vegetables, minimally processed foods, nanocomposites - BiodegradaBle packaging and ediBle coaTing for fresh-cuT fruiTs and vegeTaBles f. galgano1*, n. condelli1, f. favaTi2, v. di Bianco1, g. perreTTi3 and M.c. caruso1 1 School of Agricultural, Forestry, Food and Environmental Sciences, University of Basilicata, Viale dell’Ateneo Lucano 10, 85100 Potenza, Italy 2 Department of Biotechnology, University of Verona, Strada Le Grazie 15, 37134 Verona, Italy 3Department of Agriculture, Food and Environmental Sciences, University of Perugia, Via S. Costanzo n.c.n., 06126 Perugia, Italy *Corresponding author: Tel. +39 0971-205570, Fax +39 0971-205503, email: fernanda.galgano@unibas.it AbstrAct this work focuses on biodegradable packaging and edible coatings applied to fresh-cut fruits and vegetables and their effects on the product quality. Practical applications are mainly limited to the use of biodegradable materials that, however, do not allow full control of the product mois- ture loss. better results can be achieved by the combined use of biodegradable packagings with edible coatings and recent research has shown that enrichment with silver-montmorillonite nan- oparticles may be a promising technique. However, the actual utilization of these materials is still limited, due to the high costs of the raw materials and the limited production. 2 Ital. J. Food Sci., vol. 27 - 2015 IntroductIon In recent years, the establishment of new lifestyles, characterized by a lack of time in do- mestic preparations, has been accompanied by an evolution of the structure of food consump- tion and a destructuring of meals. therefore, the consumption of minimally processed fruits and vegetables has grown rapidly as a result of the consumer trend- “rich in cash, poor in time” (MArtÍn-dIAnA et al., 2007; conte et al., 2009). Minimally processed fruits and vegetables were developed in the 1980s to respond to the emerging consumer demand for both conve- nience and high quality aspects (del nobIle et al., 2008). these foodstuffs combine fresh-like and healthy characteristics with a minimal time of preparation before consumption (rAgAert et al., 2004). In fact, their success is also due to the beneficial health effects for the presence of an- tioxidants that act as receptors of free radicals; in particular, ascorbic acid and β-carotene are the antioxidants present in the greatest quanti- ties in fruits and vegetables (rIco et al., 2007). the minimal processing operations (“mild technology”) necessary to produce fresh-cut foods, such as peeling, cutting, washing, treat- ments with sanitizing agents, drying, alter the physical integrity of these products, making them more perishable than the original raw ma- terials (corbo et al., 2006). this is due to res- piration, transpiration, enzymatic activity of the living tissue after harvest and processing and, at the same time, to proliferation of spoilage and pathogenic microorganisms (gAlgAno et al., 2014; nguyen-tHe and cArlIn, 1994). the in- dustrial process accelerates the degradation of the minimally processed foods and leads to bio- chemical changes such as: - increasing of respiration that accelerates the oxidation processes; - degradation of cell membranes and enzy- matic browning; - loss of tissue texture. the knowledge of factors influencing quality degradation after processing of fruits and vegeta- bles is essential to develop technologies for shelf- life extending and maintaining quality during processing and distribution (corbo et al., 2006). In order to reduce the microbiological, chem- ical and physical spoilage, it is possible to act on processing or, more usually, on packaging that represents a barrier to qualitative decay of the product (gAlgAno et al., 2014). the packag- ing operation should establish inside the pack- aging an optimal atmosphere for the best pres- ervation of the product. generally, low o 2 and elevated co 2 atmospheres, associated with low storage temperature, reduce product respira- tion rate, limiting, in this way, losses in fresh weight (WAtAdA et al., 1996). therefore, a prop- er combination of product characteristics and film permeability results in the evolution of an appropriate atmosphere within packages (sMItH et al., 1987). traditionally, food companies use polymeric films (polyethylene Pe, polypropylene PP, poly- styrene, Ps) to package fresh fruits and vegeta- bles because of their large availability at rela- tively low cost and their good mechanical per- formance, good barrier to oxygen, carbon diox- ide (sIrAcusA et al., 2008). nowadays, there is a growing trend in fresh fruits and vegetables packaging sector to replace the petrochemi- cal based packaging films with more environ- mentally-friendly biodegradable materials (tHA- rAnAtHAn, 2003). the extensive use of synthet- ic packaging films has led to serious ecological problems due to their total non- biodegradabili- ty. therefore, biodegradability is not only a func- tional requirement but also an important envi- ronmental attribute. biologically-based packag- ing contains raw materials originated from agri- cultural sources, produced from renewable raw materials such as starch and bio-derived mono- mers (lucerA et al., 2010). these materials rep- resent a viable alternative because: - they are obtained from renewable sources; - they are recyclable and degradable; - they are an opportunity to reduce costs. the applications range from the design of mul- tilayer barrier coating consisting of biopolymers, to enrichment of the matrix of traditional plas- tics PP and Pe with nanocomposite materials of natural origin. However, bio-packaging still rep- resents a niche market because of the cost and poor overall performance of biodegradable films when compared to those of traditional plastic materials (del nobIle et al., 2009 a). the present work focuses on the different packaging strategies for fresh-cut fruits and vegetables. In particular, the potential appli- cations of biodegradable materials and edible coatings have been described, with their effects on the quality of these products. the applica- tion of nanotechnology, as a tool to improve the performance and thermal, barrier and mechani- cal properties of bio-polymers has also been as- sessed (Azeredo, 2009). bIo-bAsed MAterIAls For Food PAckAgIng the term “Bio-Based Materials” (BBM) is as- signed to packaging materials and to packaging produced from biological renewable raw mate- rials (PIergIoVAnnI and MAscHeronI, 2007). Polymers derived from renewable resources (biopolymers) are broadly classified according to method of production, as follows: 1. Polymers directly extracted/removed from natural materials (mainly plants). examples are polysaccharides, such as starch and cellu- lose and proteins, like casein and wheat glu- ten, and lipids. Ital. J. Food Sci., vol. 27 - 2015 3 2. Polymers produced by “classical’’ chemi- cal synthesis from renewable bio-derived mon- omers. A good example is polylactate, a biopol- yester polymerised from lactic acid monomers. the monomer itself is produced via fermenta- tion of carbohydrate feedstock. 3. Polymers produced by microorganisms or genetically transformed bacteria. the best known bio-polymer types are the polyhydroxyal- kanoates, mainly polyhydroxy butyrates and co- polymers of hydroxy-butyrate (Hb) and hydroxy- valerate (HV) (Petersen et al., 1999). the compostability attribute is very impor- tant for biopolymer materials, because compost- ing allows disposal of the packages in the soil, which is more energy efficient than recycling. during biological degradation water, carbon di- oxide and inorganic compounds without toxic residues are produced. According to the european bioplastics, biopol- ymers made with renewable resources have to be biodegradable and especially compostable, so they can act as fertilizers and soil conditioners. Whereas plastics based on renewable resources must not necessarily be biodegradable or com- postable, the bioplastic materials do not neces- sarily have to be based on renewable materials, because the biodegradability is directly corre- lated to the chemical structure of the materials rather than the origin. In particular, the type of chemical bond defines whether and in what time the microbes can biodegrade the material. sev- eral synthetic polymers are biodegradable and compostable, such as starch, cellulose, which are naturally carbon-based polymers. Vicever- sa, the bioplastics based on natural monomer, can lose their biodegradability through chemical modification like polymerization, such as for ex- ample nylon 9 type polymers obtained from po- lymerization of oleic acid monomer or Polyam- id 11 obtained from the polymerization of castor oil monomer (sIrAcusA et al., 2008). the problems associated with renewable bi- opolymers are threefold: performance, process- ing and cost. Although these factors are some- what interrelated, problems due to “performance and processing’’ are more pronounced with poly- mers extracted directly from biomass (cellulose, starch, proteins). conversely, polymers belong- ing to categories 2 and 3 above, generally per- form very well and are easily processed into films using standard plastic techniques, but tend to be expensive compared with synthetic analogues (Petersen et al., 1999). Polymers directly extracted/removed from natural materials Polysaccharides the polysaccharides show effective gas bar- rier properties although they are highly hydro- philic and show high water vapor permeability in comparison with commercial plastic films. the main polysaccharides that can be includ- ed in edible coating formulations are starch and starch derivates, cellulose derivates, alg- inate, carrageenan, chitosan, pectin, and sev- eral gums. based on the molecular level, pol- ysaccharides vary according to their molecu- lar weight, degree of branching, conformation, electrical charge and hydrophobicity. Variations in these molecular characteristics will lead to variations in the ability of different polysaccha- rides to form coatings, as well as to variations in the physicochemical properties and perfor- mance of the coatings formed. For example, the linear structure of some of these polysac- charides such as cellulose, amylose (a compo- nent of starch), and chitosan makes their films tough, flexible, transparent, and resistant to fats and oils (VArgAs et al., 2008). starch, a storage polysaccharide of cereals and legumes, is most commonly used in the for- mulation of edible coatings and films because it is inexpensive, abundant, biodegradable, and easy to use. Films based on starch have mod- erate gas barrier properties. their mechani- cal properties are generally inferior to synthet- ic polymer films. When a plasticizer, such as water, is added starches exhibit thermoplastic behavior (krocHtA and Mulder-JoHnston, 1997). starch-based thermoplastic materials have been commercialized over the last few years and today dominate the market of bio- based, compostable materials (clAus, 2000). the properties of the starch-based materials can be improved by destructuring the native conformation of the starch and adding syn- thetic substances. It is common practice to add copious amounts of synthetic polymer to the starch, such as polyvinyl alcohol (PVA) or polycaprolactone. Another important polysaccharide is chi- tosan, which is mainly obtained from crab and shrimp shells (HIrAno, 1999). Films and coat- ings based on chitosan have selective permea- bility to gases (co 2 and o 2 ) and good mechan- ical properties. However, their uses are limited mainly because of their high water vapor perme- ability (butler et al., 1996; cAner et al., 1998). Moreover, chitosan shows antifungal and anti- bacterial properties, which are believed to have originated from its polycationic nature. An edi- ble film with innovative characteristics has been obtained by combining the antimicrobial prop- erties of chitosan with the property of self-seal- ing banana starch, variety kluai namwa. the presence of starch in the composite film makes water soluble and sealable bags or wraps pos- sible, while the presence of chitosan gives them the antimicrobial property. the composite bags were found to protect asparagus, baby corn and chinese cabbage against Staphylococcus aureus activity by serving as a good barrier and as an antimicrobial agent. the properties of composite 4 Ital. J. Food Sci., vol. 27 - 2015 films were more similar to starch films than to films made solely from chitosan as the amount of banana flour was greater than chitosan in the films. these composite films were cheaper and less flexible than chitosan films. Film extensi- bility was improved by the addition of banana flour and glycerol. banana flour addition en- hanced WVP and solubility, although, the films were not completely smooth. the biodegrada- ble and hot water soluble films can be used in food packaging and to reduce microbial counts thus extending shelf-life of fruit and vegetables in convenient bags (PItAk and rAksHIt, 2011). cellulose is the most abundant natural poly- mer on earth and it is an essentially linear pol- ymer of anhydroglucose. As a consequence of its chemical structure, it is highly crystalline, fibrous, and insoluble. Many derivatives of cel- lulose have excellent properties of film-forming, but are simply too expensive for use on a large scale. Finally, the similarity of cellulose and chitosan in primary structures has facilitated the formation of homogeneous composite films. MÖller et al. (2004) reported that 1% of chi- tosan in chitosan-HPMc (hydroxypropylmethyl- cellulose) composite films is effective against L. monocytogenes. Alginates can also be used to prepare edible coatings and films. Alginates are the salts of alg- inic acid, which is a linear copolymer of d-man- nuronic and l-guluronic acid monomers. Alginate coating formation is based on the ability of algi- nates to react with di-valent and tri-valent cations such as calcium, ferrum or magnesium, which are added as gelling agents (cHA and cHInnAn, 2004). An original study (norAJIt et al., 2010) in- vestigated the physical and antioxidant proper- ties of alginate biodegradable film incorporating white, red and extruded white ginseng extracts. the major pharmacologically active constituents of ginseng are triterpene saponins called ginseno- sides. the studies demonstrate that the ginseng extract can be successfully incorporated into bio- degradable alginate films and retain excellent an- tioxidant activities. the incorporation of ginseng extract into the alginate films did not cause ma- jor changes in the moisture content values. on the other hand, significant reductions in tensile strength and elastic modulus values of ginseng- alginate film have been found compared to those of the film without ginseng extract. galactomannans, natural polysaccharides commonly used in the food industry, mostly as a stabilizer, thickener and emulsifier, are one of the alternative materials that can be used for the production of edible films/coatings based on their edibility and biodegradability. these gums are mostly obtained from the endosperm of di- cotyledonous seeds of numerous plants, par- ticularly the Leguminosae. the great advantage of galactomannans is their ability to form very viscous solutions at relatively low concentra- tions that are only slightly affected by pH, ion- ic strength and heat processing. the mechani- cal, barrier and rheological properties of galacto- mannan films/coatings may be used to improve the stability, safety, and quality of food products (cerQueIrA et al., 2011). lIMA et al. (2010) suc- cessfully blended collagen with two galactoman- nans from different species (A. pavonina and C. pulcherrima). the composition of films/coatings with different proportions of galactomannan, col- lagen and glycerol have been optimized based on the wettability of films, transport and me- chanical properties; these films have been sub- sequently used to coat mangoes and apples. the results showed that the application of the coat- ings leads to a decrease of gas transfer rates of the fruits. For mangoes, a coating of A. pavoni- na galactomannan (0.5%), collagen (1.5%) and glycerol (1.5%) decreased oxygen consumption and carbon dioxide production in 28% and 11%, respectively. For apple, the oxygen consump- tion and carbon dioxide production decreased for both gases by approximately 50%, with the utilization of a coating of C. pulcherrima galac- tomannan (0.5%) and collagen (1.5%). Proteins Proteins that have received great attention for their capability of forming edible films and coat- ings include corn zein, wheat gluten (Wg), soy protein, whey protein, casein, collagen/gelatin, pea protein, rice bran protein, cottonseed pro- tein, peanut protein, and keratin (HAn and gen- nAdIos, 2005). casein based edible coatings are attractive for food applications due to their high nutritional quality, excellent sensory properties, and strong potential for providing food products with adequate protection against their surround- ing environment. Whey proteins have been sub- jected to intense investigation over the past dec- ade or so. With the addition of plasticizer, heat- denatured whey proteins produce transparent and flexible water-based edible coatings with excellent oxygen, aroma, and oil barrier prop- erties at low relative humidity. However, the hy- drophilic nature of whey protein coatings caus- es them to be less effective as moisture barriers (VArgAs et al., 2008). the water vapor permea- bility limits their potential uses for food packag- ing and justifies the interest in natural hydro- phobic substances, such as lipids. Lipids edible lipids used to develop edible coatings are: beeswax, candelilla wax, carnauba wax, tri- glycerides, acetylated monoglycerides, fatty ac- ids, fatty alcohols, and sucrose fatty acid es- ters. lipid coatings and films are mainly used for their hydrophobic properties, representing a good barrier to moisture loss. this factor is ex- tremely important, as a great number of stud- ies deal with the use of coatings on fresh fruits Ital. J. Food Sci., vol. 27 - 2015 5 and vegetables to control their desiccation. In addition to preventing water loss, lipid-based coatings have been used to reduce respiration, thereby extending shelf life and to improve ap- pearance by generating a shine on fruits and vegetables. In contrast, the hydrophobic char- acteristic of lipids forms thicker and more brit- tle films. consequently, they must be associat- ed with film forming agents such as proteins or cellulose derivatives (debeAuFort et al., 1993). Polymers produced by “classical” chemical synthesis from renewable bio-derived monomers Aliphatic polyesters belong to this catego- ry and are obtained from bio-derived mono- mers by means of classical polymerization pro- cedures. one of the most promising biopolymer is the poly(lactic acid) (PlA), which is derived from the controlled depolymerization of the lac- tic acid monomer, obtained from the fermenta- tion of sugar feedstock, corn, etc., which are re- newable resources readily biodegradable (cAbe- do et al., 2006). discovered in 1932 by cArotH- ers (JAMsHIdIAn et al., 2010), it is a versatile polymer, recyclable and compostable, with high transparency, high molecular weight, good pro- cessability and water solubility resistance. In comparison to other biopolymers, the produc- tion of PlA has numerous advantages including: a) production of the lactide monomer from lactic acid, which is produced by fermentation of a renewable agricultural source corn (usual- ly based on the strain of Lactobacillus); b) fixation of significant quantities of carbon dioxide via corn (maize) production by the corn plant; c) significant energy savings; d) the ability to recycle back to lactic acid by hydrolysis or alcoholysis; e) the ability to tailor physical properties through material modification (dorgAn et al., 2000). PlA is generally recognized as safe (grAs) by the united state Food and drug Administration (FdA). Moreover, PlA can be easily processed by conventional processing techniques used for thermoplastics like injection moulding, blow moulding, thermoforming and extrusion. PlA can be used in a wide range of applications; the major PlA application today regards packaging (nearly 70%). PlA food packaging applications are ideal for fresh products, such as fresh meat (gAlgAno et al., 2009) or fruits and vegetables. Polymers produced by microorganisms: polyhydroxyalkanoates (PHA) In recent years poly-β-hydroxyalkanoates (PHA) have attracted a lot of attention as biocom- patible and biodegradable thermoplastic mate- rials with potential applications. Poly(3-hydroxybutyrate) (PHb) is one of the well-known biodegradable poly(hydroxy al- kanoates) (PHA). PHb is a natural thermoplas- tic polyester and has many mechanical proper- ties comparable to synthetically produced de- gradable polyesters such as the poly-l-lactides (FreIer et al., 2002). since 1925 PHb has been produced by bacterial fermentation (rosA et al., 2004), which takes place in the presence of a wide variety of bacteria, as intracellular reserve material. At least 75 different genera of bacte- ria have been known to accumulate PHb as in- tracellular granules. this polymer is synthesized under limited culture conditions and its pro- duction has most commonly been studied with microorganisms belonging to the genera Alca- ligenes, Azobacter, Bacillus and, Pseudomonas (ugur et al., 2002). PHb films are degraded by numerous microorganisms (bacteria, fungi and algae) in various ecosystems. When in contact with the polymer, the microorganisms secrete enzymes that break it into successively small- er segments, thereby reducing the average mo- lecular weight (buccI et al., 2005). these pol- ymers, alone or in combination with synthetic plastic or starch produce excellent packaging films. the polyalkanoates are more hydropho- bic than the polysaccharide-based materials, re- sulting in a material with good moisture barrier properties, whereas the gas barriers are inferior (Petersen et al., 1999). PHb has been used in small disposable products and in packing ma- terials. However, little is known about the ap- plication of PHb to packaging for food products. this polymer is not used in cut-fruits and vege- tables, so there is no sense to have it here, un- less you write some possible uses in cut-fruits and vegetables. Another biopolymer produced from microor- ganisms is the pullulan, extracted from cells of Aureobasidium pullulans, Tremella mesenterica and Cyttaria harioti. It is characterized by high resistance to fats, good barrier to gases; more- over, it is completely biodegradable and can be processed with conventional techniques. chemi- cally pullulan is a polymer of maltotriose used in combination with sorbitol and fatty acids ester- ified with sucrose to achieve edible coatings for fruits (PIergIoVAnnI and MAscHeronI, 2007). In a recent study the possibility of using new bi- odegradable material such as kefiran, a microbi- al polysaccharide obtained from the flora of ke- fir grains has been investigated (gHAseMlou et al., 2011). It is a water-soluble polysaccharide containing approximately equal amounts of glu- cose and galactose (MIcHelI et al., 1999), used in the food industry as a texturing agent and gelling agent. It could be a viable alternative to synthetic materials for food packaging, also be- cause it has antibacterial and anticancer prop- erties (MAedA et al., 2004). the biopolymers fulfill environmental require- ments, but show some limitations in terms of 6 Ital. J. Food Sci., vol. 27 - 2015 performance, such as thermal resistance, me- chanical properties and barrier properties, as- sociated with high costs. so, more research needs to be carried out on the packaging mate- rial with a view to introducing, for instance, in- telligent molecules or inorganic material, pref- erably in the form of nano-particles, in order to expand the range of properties of the materials. the protagonist of the twenty-first century is an- other scientific innovation that is affecting the packaging industry: nanotechnology. nAnotecHnology And nAnocoMPosItes the concept of nanotechnology was intro- duced by rIcHArd FeyMAn in 1959 at a meet- ing of the American Physical society (kHAdeM- HosseInI and lAnger, 2006). nanotechnology is defined as “the design, characterization, pro- duction and application of structures, devices and systems by controlling the shape and size at the nanometer scale” (royal society and royal Academy of engineering, nanoscience and na- notechnologies, 2004). nanotechnology and its application in food science have recently been studied by several researchers. the use of nan- oparticles, such as micelles, liposomes, nanoe- mulsions, biopolymeric nanoparticles aimed at ensuring food safety, are some novel nano-food applications. nanotechnology is also applica- ble in the context of food packaging: however, the use of edible and biodegradable polymers has been limited because of problems related to performance (such as brittleness, poor gas and moisture barrier), processing (such as low heat distortion temperature), and cost. the applica- tion of nanotechnology to these polymers may open new possibilities for improving not only the properties but also the cost-price-efficien- cy (sorrentIno et al., 2007). the use of fillers with at least one nanoscale dimension (nano- particles) produces nanocomposites. Most re- inforced materials present poor matrix–filler in- teractions, which tend to improve with decreas- ing filler dimensions. nanoparticles have propor- tionally a larger surface area than their micro- scale counterparts, which favors the filler–ma- trix interactions and the performance of the re- sulting material. Polymer composites are mixtures of polymers with inorganic or organic fillers with certain ge- ometries (fibers, flakes, spheres, particulates). A uniform dispersion of nanoparticles leads to a very large matrix/filler interfacial area, which changes the molecular mobility, the relaxation behavior and the consequent thermal and me- chanical properties of the material. Although several nanoparticles have been recognized as possible additives to enhance polymer perfor- mance, the packaging industry has focused its attention mainly on layered inorganic solid like clay and silicates, due to their availability, low cost and relative simple processability (Azere- do, 2009). the most widely studied type of clay fillers is montmorillonite (MMt), a hydrated alu- mina-silicate layered clay consisting of an edge- shared octahedral sheet of aluminum hydrox- ide between two silica tetrahedral layers (WeIss et al., 2006). MMt is an effective reinforcement filler, due to its high surface area and large as- pect ratio (50–1000) (uyAMA et al., 2003). Fur- thermore, the presence of this nanoclay in pol- ymer matrix increases its degradation rate, due to hydroxyl groups of MMt (souzA et al., 2013). MAngIAcAPrA et al. (2005) reported that it is possible to reduce the oxygen permeability by adding clay montmorillonite to pectins. Also the combination of PlA film with MMt-layered sil- icates may be useful to create a nanocompos- ite material with good barrier properties (sou- zA et al., 2013). Moreover, a starch/clay nanocomposite film have been obtained by dispersing MMt nano- particles via polymer melt processing techniques (AVellA et al., 2005). the results related to me- chanical characterization showed an increase of modulus and tensile strength. besides nano-reinforcements, nanoparticles can have other functions when added to a poly- mer, such as antimicrobial activity, enzyme im- mobilization, biosensing (Azeredo, 2009). the incorporation of antimicrobial compounds into food packaging materials has received consider- able attention. Films with antimicrobial activi- ty could help control the growth of pathogenic and spoilage microorganisms. An antimicrobi- al nanocomposite film is particularly desirable due to its acceptable structural integrity and barrier properties imparted by the nanocom- posite matrix, and the antimicrobial properties contributed by the natural antimicrobial agents impregnated within (rHIM and ng, 2007). the most common nanocomposites used as antimi- crobial films for food packaging are based on silver, which is well known for its strong tox- icity towards a wide range of microorganisms (lIAu et al., 1997), with high temperature sta- bility and low volatility (kuMAr and MÜnstedt, 2005). some mechanisms have been proposed for the antimicrobial property of silver nan- oparticles (Ag-nPs): adhesion to the cell sur- face, degrading lipopolysaccharides and form- ing ‘‘pits’’ in the membranes, largely increas- ing permeability (sondI and sAloPek-sondI, 2004); penetration inside bacterial cell, dam- aging dnA (lI et al., 2008); and releasing anti- microbial Ag+ ions by Ag-nPs dissolution (Mo- rones et al., 2005). Moreover, Ag-nPs absorbs and decomposes ethylene (Hu and Fu, 2003), which may contribute to its effects on extend- ing shelf life of fruits and vegetables. Indeed, lI et al. (2009) reported that a nanocomposite Pe film with Ag-nPs can retard the senescence of jujube, a chinese fruit. An et al. (2008) re- ported that a coating containing Ag-nPs is ef- Ital. J. Food Sci., vol. 27 - 2015 7 fective in decreasing microbial growth and in- creasing shelf life of asparagus. the three new requirements of food packaging are the following: “bioactive, biodegradable and bionanocomposite”. However, there are many safety concerns about nanomaterials, as their size may allow them to penetrate into cells and eventually remain in the system. one can as- sume that the application of nanoparticles with an antimicrobial function (the nanoparticles of silver or copper) poses the risk the consumer’s direct exposure to metals. Although the migra- tion of metals from biodegradable nanocom- posite film of starch / clay applied to vegetable products is considered to be minimal (AVellA et al., 2005), it is necessary to have more accu- rate information about the likely impact on hu- man health. In fact, many studies and experi- ments relating to the use of nanoparticles are still in progress in order to avoid premature gen- eralizations that could undermine the potential benefits obtainable from this technology. In the next section, the potential applications of this new category of materials (biodegradable, edible coating and nanocomposites) and their possible effects on the quality characteristics of fresh-cut fruit and vegetables is discussed. edIble FIlMs And coAtIngs For FresH-cut FruIts And VegetAbles consumers usually judge the quality of fresh- cut fruit on the basis of appearance and fresh- ness at the time of purchase (kAder, 2002). However, minimal processing operations alter the integrity of fruits, with negative effects on product quality, such as browning, off-flavour development and texture breakdown. Also, the presence of microorganisms on the fruit surface may compromise the safety of fresh-cut fruit. traditionally, edible coatings have been used in the fresh-cut industry as a strategy to reduce the deleterious effects that minimal processing imposes on intact vegetable tissues. An edible coating may be defined as a thin layer of material that covers the surface of the food and can be eaten as part of the whole prod- uct. therefore, the composition of edible coat- ings must be conform to the regulation that ap- ply to the food product concerned (guIlbert et al., 1995; VArgAs et al., 2008). edible coatings may contribute to extend the shelf-life of fresh-cut fruits by reducing mois- ture and solute migration, gas exchange, respi- ration and oxidative reaction rates, as well as by reducing or even suppressing physiological dis- orders (bAldWIn et al., 1996; PArk, 1999). ed- ible coatings are capable of producing a modi- fied atmosphere on coated fruits by isolating the coated product from the environment. coatings with selective permeability to gases are capable of decreasing the interchange of o 2 and co 2 be- tween coated fruits and the environment (olIVAs and bArbosA-cÁnoVAs, 2005). High co 2 con- centration within fruit tissues also delays rip- ening by decreasing the synthesis of ethylene, a hormone essential for ripening (sAltVeIt, 2003). lee et al. (2003) demonstrated that the respi- ration rate of apple slices decreases 20% when coated with a film based on whey protein. ed- ible coating based on aloe vera reduced respi- ration rate and microbial spoilage in sliced ki- wifruit (benÍtez et al., 2013). Fresh-cut prod- ucts are characterized by high water transpira- tion rates and the creation of a moisture and gas barrier may lead to weight loss and respiration rate reduction, with a consequent general delay of produce senescence (VAlencIA-cHAMorro et al., 2011). coating apple slices with a carbohy- drate/lipid bilayer film reduces water loss dur- ing storage between 12 to 14 times when com- pared to the water loss suffered by uncoated ap- ple slices in similar storage conditions (Wong et al., 1994). Alginate coatings prevented water loss on fresh-cut apple (lee et al., 2003; Fontes et al., 2007), papaya (tAPIA et al., 2007), pear (oMs- olIu et al., 2008a), and melon (oMs-olIu et al., 2008b). chitosan coatings reduced water loss in sliced mango (cHIen et al., 2007) and carrageen- an coatings prevented water loss on sliced ba- nana (bIco et al., 2009). the cassava starch ed- ible coating with or without the calcium lactate was able to reduce weight loss in fresh-cut pine- apple (bIerHAls et al., 2011), while the cassava starch edible coating with or without potassium sorbate decreased the respiration rate in fresh- cut strawberries (gArcIA et al., 2010). Minimally processed pummelo (Citrus Maxima Merr.), coat- ed with starch-based coatings (derived from cas- sava and rice) had a lower weight loss of 4.8– 7.7% compared to the control (non-coated min- imally processed pummelo) (kerdcHoecHuen et al., 2011). Moreover, the combination of citric acid dipping and cassava starch or sodium algi- nate edible coatings was able to delay the qual- ity deterioration of fresh-cut mangoes, decreas- ing the respiration rate of fruits with value up to 41% lower than the control fruit. Although the citric acid increases the weight loss of the prod- uct, causing a partial dehydration of the vege- table tissue, the use of cassava starch and algi- nate coatings was able to hinder this undesira- ble effect of citric acid, presenting a lower weight loss than the coated samples (cHIuMArellI et al., 2011). In a previous work, cHIuMMArellI et al. (2010) reported that this treatment provided a better maintenance of colour characteristics, due to the combined effect of citric acid dipping and cassava starch coating. citric acid delayed browning along the storage and the edible coat- ings acted as a gas barrier, decreasing the res- piration rate of mango pieces and, consequent- ly the formation of carotenoids. Moreover, another important advantage of ed- ible coating is the reduction of synthetic packag- 8 Ital. J. Food Sci., vol. 27 - 2015 ing waste, because these coatings are composed of biodegradable raw material (dHAll, 2013). the properties of edible coating depend pri- marily on molecular structure rather than mo- lecular size and chemical constitution. specific requirements for edible films and coatings are as follows (ArVAnItoyAnnIs and gorrIs, 1999): - the coating should be water-resistant so that it remains intact and covers a product adequate- ly, when applied; - it should not deplete oxygen or build up ex- cessive carbon dioxide. A minimum of 1–3% ox- ygen is required around a commodity to avoid a shift from aerobic to anaerobic respiration; - it should reduce water vapor permeability; - it should melt above 40°c without decom- position; - it should be easily emulsifiable, non-sticky or should not be tacky, and have efficient dry- ing performance; - it should never interfere with the quality of fresh fruit or vegetable and not impart undesir- able order; - it should have low viscosity and be econom- ical; - it should be translucent to opaque but not like glass and capable of tolerating slight pres- sure. the ability of edible coatings to preserve the quality of fresh-cut products may vary from product to product, then it is necessary to con- sider the variety and maturity of the prod- uct, food surface coverage, storage conditions and composition and thickness of the coating (gonzÁlez-AguIlAr et al., 2010). According to their components, edible films and coatings can be divided into three catego- ries: hydrocolloids, lipids, and composites. Hy- drocolloids include proteins and polysaccha- rides, while lipids include waxes, acylglycerols, and fatty acids. composites contain both hydr- ocolloid components and lipids. their presence and abundance determine the barrier proper- ties of material with regard to water vapor, ox- ygen, carbon dioxide, and lipid transfer in food systems. However, none of the three constitu- ents can provide the needed protection by them- selves and so are usually used in a combination for best results (McHugH et al.,1994; guIlbert et al., 1996). the main objective of producing composite films is to improve the permeability or mechanical properties according to specific applications. these heterogeneous films are ap- plied either in the form of an emulsion, suspen- sion, or dispersion of the non miscible constitu- ents, or in successive layers (multilayer coating or films), or in the form of a solution in a com- mon solvent. several other compounds such as plasticizers and emulsifiers may be added to ed- ible films and coatings to improve their mechan- ical properties and form stable emulsions when lipids and hydrocolloids are combined (VAlen- cIA-cHAMorro et al., 2011). the application of edible coatings to fresh-cut fruits must address the problem regarding the difficult adhesion of materials to the hydrophilic surface of the sliced fruit. the layer-by-layer (lbl) electrodeposition can solve this problem (WeIss et al., 2006). lbl assembly, which is performed by alternating the immersion of substrates in solutions of opposite- ly charged polyelectrolytes with rinsing steps, produces ultrathin polyelectrolyte multilayers on charged surfaces. A requirement for multi- layer formation is that the addition of an oppo- site charged polyelectrolyte to a charged sur- face results in a charge reversal, which permits the successive deposition of oppositely charge polyelectrolytes. chitosan, poly-l-lysine, pec- tin, and alginate are the most common biopoly- mers that can be used in the formation of these multilayered structures (MArudoVA et al., 2005; krzeMIskI et al., 2006; bernAbÉ et al., 2005). In a study of MAntIllA et al. (2013), an alginate- based multilayered coating (developed using the layer-by-layer technique) enhanced the quality and shelf-life of fresh-cut pineapple extending its shelf-life to 15 days at 4°c. the main advantage of using edible films and coatings is that several active ingredients (such as antimicrobials, antibrownings, texture en- hancer and nutraceuticals) can be incorporat- ed into the polymer matrix and consumed with the food, thus enhancing safety or even nutri- tional and sensory attributes (roJAs-grAÜ et al., 2009). Antimicrobial agents Fresh-cut fruits are more perishable than their corresponding whole uncut commodities due to wounding during preparation (brecHt, 1995). the physical and chemical barrier pro- vided by the epidermis, which prevents the de- velopment of microbes on the fruit surface, is removed during processing. there are several categories of antimicrobi- als that can be potentially incorporated into ed- ible films and coatings, including organic acids (acetic, benzoic, lactic, propionic, sorbic), fat- ty acid esters (glyceryl monolaurate), polypep- tides (lysozyme, peroxidase, lactoferrin, nisin). esWArAnAndAM et al. (2006) incorporated mal- ic and lactic acid into soy protein coatings aim- ing to evaluate its effect on the sensory quali- ty of fresh-cut cantaloupe melon, without stud- ying the antimicrobial effect of the coating. In general, organic acids incorporated in films did not adversely affect the sensory properties of coated fruit. With reference to the use of natural antimi- crobials, the development of coatings which use inherently antimicrobial polymers as a support matrix is very promising. For example, chitosan, produced from the deacetylation of crustacean chitin (poly-β-(1→4)-n-acetyl-d-glucosamine), is one of the most effective antimicrobial film Ital. J. Food Sci., vol. 27 - 2015 9 forming biopolymers. chitosan is a cationic pol- ysaccharide, which, among other antimicrobial mechanisms, promotes cell adhesion by the in- teraction of the positive-charged amines with the negative charges in the cell membranes, causing leakage of intracellular constituents (HelAnd- er et al., 2001). chitosan based coatings were shown to protect highly perishable fruits like strawberries, raspberries, grapes and fresh-cut- green pepper from fungal decay. (VArgAs et al., 2006; el gAoutH et al., 1991; zHAng and QuAn- tIck, 1998; roMAnAzzI et al., 2002; deVlIegHe- re et al., 2004; PArk et al., 2005, rAyMond et al., 2012). the application of chitosan edible coating on fresh-cut broccoli (MoreIrA et al., 2011a) significantly reduced mesophilic and psychro- trophic counts and inhibited the growth of to- tal coliform with respect to the control samples, throughout the whole storage period. similar re- sults were reported by gerAldIne et al. (2008) working with minimally processed garlic. At the end of the storage, yeasts and molds were the most dominant flora and represented the larg- est part of the total aerobic count in broccoli. on the contrary, durAngo et al. (2006) found- ed an important fungicidal action of chitosan applied on minimally processed carrot. Moreo- ver, the application of mild heat shock enhanced the chitosan inhibition action (MoreIrA et al., 2011b). From a sensory point of view, the chi- tosan inhibited the yellowing and opening florets of fresh-cut broccoli. Moreover, chitosan-based edible coatings can also be used to carry other antimicrobial compounds such as organic ac- ids (outtArA et al., 2000), essential oils (zIVA- noVIc et al., 2005), spice extracts (PrAnoto et al., 2005), lysozyme (PArk et al., 2004) and nisin (PrAnoto et al., 2005; cHA et al., 2003). essen- tial oils (eos) (cinnamon, oregano, lemongrass) stand out as an alternative to chemical preserv- atives and their use in foods meets the demands of consumers for natural products. burt (2004) reported that hydrophobicity is an important characteristic of eos, which makes them able to pass through cell membranes and enter mi- tochondria, disturbing the internal structures and rendering the membranes more permeable. yet the application of eos in foods is limited due to their impact on organoleptic food prop- erties, variability of their composition, and their variable activity in foods due to interactions with food components. nevertheless, the use of eos to control microbial growth in foods has been proposed for several products including fresh- cut fruits and vegetables. rAybAudI-MAssIlIA et al. (2008b) studied the effect of malic acid and essential oils of cinna- mon, palmarosa and lemongrass as natural an- timicrobial substances incorporated into an al- ginate-based edible coating on the shelf-life of fresh-cut melon. the coating containing malic acid was effective in improving the shelf-life of fresh-cut melon from both the microbiological and physicochemical points of view in compar- ison with non-coated fresh-cut melon samples. the incorporation of the essential oils or their active compounds into the coating prolonged the microbiological shelf-life by more than 21 days in some cases, probably due to an enhanced an- timicrobial effect of malic acid and the essential oils. However, some physicochemical character- istics, such as firmness and color, and also some sensory quality attributes were adversely affect- ed, causing a significant reduction of fresh-cut melon shelf-life. In contrast, when malic or lactic organic acids incorporated in soy protein coat- ings were applied to fresh-cut cantaloupe, they did not adversely affect the sensory properties of the fruit after cold storage (esWArAnAndAM et al., 2006). AyAlA-zAVAlA et al. (2013), developed an edible pectin film enriched with the essential oil from cinnamon leaves and proved that this application can increase the antioxidant status and reduce bacterial growth of fresh-cut peach. chitosan coatings enriched with bioactive com- pounds (bee pollen, ethanolic extract of propo- lis, pomegranate dried extract, resveratrol)/es- sential oils (tea tree, rosemary, clove, oreganum, lemon aloe vera calendula) could be a good al- ternative for controlling not only the microor- ganisms present in broccoli, but also the sur- vival of E. coli and L. monocytogenes inoculat- ed in the product, without introducing delete- rious effects on the sensory attributes of mini- mally processed broccoli (AlVArez et al., 2013). roJAs-grAu et al. (2006, 2007a) have stud- ied the effects of oregano, cinnamon, and lemon- grass oils and their active compounds (carvacrol, cinnamaldehyde and citral) incorporated into ap- ple puree and alginate apple puree edible films against Escherichia coli o157:H7. In these works, oregano oil or its active compound, carvacrol, was most effective against E. coli o157:H7. In line with these preliminary studies, roJAs-grAu et al. (2007b) combined the efficacy of alginate and gellan edible coatings with the antimicro- bial effect of eos (lemongrass, oregano oil and vanillin) to prolong the shelf-life of fresh-cut ap- ples. A 4 log reduction of the inoculated popu- lation of Listeria innocua in fresh-cut apple was observed when lemongrass or oregano oils were incorporated into an apple puree alginate edi- ble coating. In addition, the coating reduced res- piration rate and ethylene production of coat- ed fresh-cut apples. In a later work (rAybAu- dI-MAssIlIA et al., 2008a), the addition of cin- namon, clove and lemongrass essential oils or their active compounds, cinnamaldehyde, euge- nol and citral into an alginate-based coating in- creased their antimicrobial effect, reduced the population of E. coli 0157:H7 by more than 4 log cFu/g and extended the microbiological shelf- life of “Fuji” apples for at least 30 days. Accord- ing to these studies, AzArAkHsH et al. (2014), observed that the lemongrass incorporated into 10 Ital. J. Food Sci., vol. 27 - 2015 an alginate-based coating for fresh-cut pineap- ple, reduces the microbial growth of the prod- uct during storage time. According to the Insti- tute of Food science and technology (IFst), 106 cFu/g is considered the limit of acceptance for shelf-life of fruit-based products (bIerHAls et al., 2011). In fact, the coated samples with 0.3% and 0.5% lemongrass reached 106 cFu/g after 12 and 16 days, respectively. on the contrary, the application of tapioca starch/decolorized hsian-tsao leaf gum coatings on minimally pro- cessed carrots with antimicrobial agents (cinna- mon oil and grape seed extract) had no benefi- cial effect on controlling the mesophile aerobics and psychrophiles. As a result, the respiration rate of the product increased (lAI et al., 2013). Instead, in the case of fresh-cut “Fuji” apples, cinnamon oil incorporated in tapioca starch/de- colorized hsian-tsao leaf gum (dHg) based edi- ble coatings, significantly reduced the growth of microorganisms, respiration rate, co 2 and eth- ylene production (PAn et al., 2013). MAntIllA et al. (2013) studied the effects of a multilayered edible coating with a microencapsulated anti- microbial complex (beta-cyclodextrin and trans- cinnamaldehyde) on the quality and shelf-life of fresh-cut pineapple. they reported that trans- cinnamaldehyde affects the pineapple flavour. However, the application of this antimicrobial coating extended the shelf-life of samples to 15 days at 4°c by inhibiting microbial growth. the same edible coating was applied on fresh-cut watermelon (sIPAHI et al., 2013) and similar re- sults were obtained: this type of alginate coat- ings extended the shelf life of fresh-cut water- melon from 7 (control) to 12-15 days. A micro- encapsulated beta-cyclodextrin and trans-cinna- maldehyde complex was also incorporated into a multilayered edible coating made of chitosan and pectin. this coating extended the shelf life of fresh-cut papaya up to 15 days at 4°c while uncoated fruits did not last this long (< 7days). Moreover, the coating reduced the losses of vi- tamin c and the total carotenoid content (brA- sIl et al., 2012). Antibrowning agents Fresh-cut fruit processing operations can in- duce undesirable changes in colour and appear- ance of these products during storage and mar- keting. the phenomena is usually caused by the enzyme polyphenol oxidase (PPo), which in the presence of oxygen, converts phenolic com- pounds into dark colored pigments (zAWIstoWs- kI et al., 1991). Application of antioxidant treat- ments such as dipping after peeling and/or cut- ting is the most common way to control brown- ing of fresh-cut fruits. Ascorbic acid is the most extensively used to avoid enzymatic browning of fruit due to the reduction of the o-quinones, generated by the action of the PPo enzymes, back to the phenolic substrates (MceVIly et al., 1992). For example, the antioxidants citric and ascorbic acid were incorporated into methyl- cellulose-based edible coatings in order to con- trol oxygen permeability and reduce vitamin c losses in apricots during storage (AyrAncI and tunc, 2004). the combination of chitosan coat- ing and sodium chlorite dip treatment on pear slices adversely affected the quality of the fruit, accelerating the discoloration of cut surfaces and increasing the PPo activity. on the con- trary, coating sodium chlorite-treated samples with carboxymethyl chitosan significantly pre- vented the browning reaction and inhibited PPo activity. (XIAo et al., 2011). the effect of coat- ings in combination with anti-browning agents (1% chitosan; 2% ascorbic acid + 0.5% cacl 2 ) on minimally processed apple slices has been studied during storage by HAIPIng et al. (2011). chitosan-coating treatments effectively retard- ed enzymatic browning on minimally processed apples during storage and effectively retarded tissue softening. As an alternative to ascorbic acid, several thi- ol-containing compounds, such as cysteine, n- acetylcysteine, reduced glutathione and 4-hex- ylresorcinol have been investigated as inhibitors of enzymatic browning (gorny et al., 2002; son et al., 2001). these compounds react with qui- nones formed during the initial phase of enzy- matic browning reactions to yield colorless ad- ditional products or to reduce o-quinones to o- diphenols (rIcHArd et al., 1992). 4-hexylres- orcinol, in combination with sodium erythor- bate, was effective in maintaining the color of pear slices “Anjou” (colellI and elIA, 2009). Furthermore, carboxylic acids (citric acid and oxalic acid) have also been suggested as effec- tive antioxidant agents in fresh-cut fruits (JI- Ang et al., 2004; PIzzocAro et al., 1993; son et al., 2001). the incorporation of antibrowning agents into edible coatings applied on fresh-cut fruits has been studied by various authors. the application of alginate edible coating in con- junction with antibrowning agents (ascorbic and citric acid) to mango cubes increased vita- min c content compared to mango cubes treat- ed only with alginate coating or control cubes, preserving the color of fresh-cut mangoes and increasing the antioxidant potential of cubes (robles-sÁncHez et al., 2013). Moreover, Pe- rez-gAgo et al., (2006) reported a substan- tial reduction in browning of fresh-cut apples when using a whey protein concentrate-bees- wax coating containing ascorbic acid, cysteine or 4-hexylresorcinol. they observed a signifi- cant improvement of the efficiency of antioxi- dant agents when incorporated into the coating formulation, being the most effective treatment with 0.5% cysteine. brAncolI and bArbosA-cÁ- noVAs (2000) decreased surface discoloration of apple slices with maltodextrin and methylcel- lulose coatings including ascorbic acid. bAld- WIn et al. (1996) found that a carboxymethyl Ital. J. Food Sci., vol. 27 - 2015 11 cellulose-based coating with addition of several antioxidants, including ascorbic acid, reduced browning and retarded water loss of cut ap- ple more effectively than an aqueous solution of antioxidants. Furthermore, roJAs-grAÜ et al. (2008) observed that both alginate and gel- lan edible coatings containing n-acetylcysteine prevented apple wedges from browning during 21 days of storage. More recently, the applica- tion of konjac glucomann (polysaccharide de- rived from the tuber of konjac, Amorphophallus konjac) with pineapple fruit extract represents an effective alternative to prevent browning of fresh-cut taaptimjaan rose apple fruit during storage. this coating enhanced total phenols and inhibited both PPo and peroxidase (Pod) activities (suPAPVAnIcH et al., 2012). or even, pullulan-based coating treatments in combina- tion with antibrowning and antibacterial agents (1% pullulan; 0.8% glutathione + 1% chitooli- gosaccharides) effectively inhibited enzymatic browning, retarded tissue softening, inhibited microbial growth, decreased weight loss and respiration rate of the minimally processed ap- ple slices (Wu and cHen, 2013). Nutraceuticals nutraceuticals can also be incorporated into the formulation of edible coatings. despite the growing interest in incorporating nutraceuti- cal compounds into food products, few stud- ies have suggested their integration into edible films or coatings. In this sense, the concentra- tion of nutrients added to the films/coatings must be carefully studied since it is important to know the effects on their basic functionality, namely on their barrier and mechanical prop- erties. some studies have reported the effect of the addition of active compounds in the func- tionality of edible films. For instance, MeI and zHAo (2003) evaluated the feasibility of milk protein-based edible films to carry high con- centrations of calcium (5 or 10% w/v) and vi- tamin e (0.1% or 0.2% w/v). they concluded that protein-based edible films can carry active compounds, although the film functionality can be compromised. In contrast, PArk and zHAo (2004) reported that the water barrier proper- ty of the chitosan-based films was improved by increasing the concentration of mineral (5and 20% w/v zinc lactate) or vitamin e in the film matrix. nevertheless, the tensile strength of the films was affected by the incorporation of high concentrations of calcium or vitamin e, although other mechanical properties, such as film elongation, puncture strength, and punc- ture deformation, were not affected. several researchers have endeavoured to incorporate minerals, vitamins and fatty acids into edible film and coating formulations to enhance the nutritional value of some fruits and vegetables, where these micronutrients are present in low quantities. tAPIA et al. (2008) reported that the addition of ascorbic acid (1% w/v) to the algi- nate and gellan based edible coatings helped to preserve the natural ascorbic acid content in fresh-cut papaya, thus helping to maintain its nutritional quality throughout storage. In the last few years, attention has been paid to the addition of probiotics to obtain functional edi- ble films and coatings. tAPIA et al. (2007) devel- oped the first edible films for probiotic coatings on fresh-cut apple and papaya, observing that both fruits were successfully coated with algi- nate or gellan film-forming solutions contain- ing viable bifidobacteria. In fact, values high- er than 106 cfu/g Bifidobacterium lactis bb-12 were maintained for 10 days during refrigerated storage of both papaya and apple pieces, dem- onstrating the feasibility of these polysaccha- ride coatings to carry and support viable pro- biotics on fresh-cut fruits. Alginate offers the possibility of formulating a broad range of functional and innovative food products, increasing the nutritional properties of foods. recently, an edible alginate coating con- taining prebiotics such as oligofructose and in- ulin has been applied on fresh-cut apples wedg- es. Fructan analysis showed that all prebiotics remained stable over the 14 day storage period and sensory and visual assessment indicated acceptable quality of apple wedges coated with prebiotics (rÖßle et al., 2011). the addition of prebiotics could be especially appealing to con- sumers as they are essential to human nutrition in the context of dietary guidelines. However, more studies are necessary to un- derstand the interactions among active ingre- dients and coating materials when developing new edible film and coating, before they are ap- plied to the surface of a real food system (ro- JAs-grAÜ et al., 2009). Further progress comes from nanotechnolo- gy, a science that could provide new techniques for extending the shelf-life of foods. Among the inorganic agents, silver nanoparticles have re- ceived great attention from the scientific world, due to the high biocidal effects towards many species of microorganisms (kIM et al., 2007). In a study by costA et al. (2012), the effects of both active calcium-alginate coating loaded with sil- ver-montmorillonite (Ag-MMt) nanoparticles and film barrier properties on the shelf-life of fresh- cut carrots were assessed. the results of this study suggest that the active coating is the best treatment and could be used to control both de- hydration and microbial spoilage of minimally processed carrots. Moreover, the combination of coating with Ag-MMt controlled the microbi- al growth better than the sole coating treatment. the combined use of proper packaging and ac- tive coating allowed the carrots to be kept in a good state of preservation thus prolonging the shelf-life to about 70 days, with respect to the uncoated samples (about 4 days). However, the 12 Ital. J. Food Sci., vol. 27 - 2015 toxicological aspects of silver nanoparticles are well known (kIrubA et al., 2010; lu et al., 2010); eu safety regulation limits the silver amount to 0.05 mg Ag/kg of food (FernAndez et al., 2009). the application of edible coating either on fresh-cut apples or on fruits and vegetables are respectively summarized in table 1 and in ta- ble 2 (a and b). table 1 - Application of edible coating on fresh-cut apple. Food product Coating Composition Main results References “Gala” apple Alginate Alginate Low weight loss; low enxymatic browning; great- er firmness OLIVAS et al. (2007) Fresh-cut “Fuji” apple Cinnamon, clove, lemon- grass essential oil or their their active compound cinnamaldehyde, eugenol and citral 4 log reduction of the E.coli O157:H7population; shelf-life ex- tension at least 30 days RAYBAUDI-MASSIL- IA et al. (2008) Fresh-cut apple wedges Prebiotics, such as oligo- fructose and inulin All prebiotics remained stable over the 14 days; good sensory characteristics RÖßLE et al. (2011) Fresh-cut “Fuji” apple Alginate and gellan Essential oils: lemongrass, oregano oil and vanillin 4 log reduction of the inoculated population of Listeria innocua; l owe r re s p i ra t i o n ra te a n d ethylene production ROJAS-GRAÜ et al. (2007b) Fresh-cut apple Alginate or gellan film-form- i n g s o l u t i o n c o n t a i - ning viable Bifidobacteria Higher values higher than 10^6 cfu/g of Bifidobacterium lactis Bb-12 were maintained for 10 days during refrigerate storage TAPIA et al. (2007) Fresh-cut apple N-acetylcysteine Enzymatic browning prevention during 21 days of storage ROJAS-GRAÜ et al. (2008) Apple slices Methylcellulose coatings Maltodextrin and ascorbic acids. Decreased surface discoloration of apples slices B R A N C O L I e t a l . (2000) Fresh-cut apple Whey protein Concentrate beeswax Ascorbic acid, cysteine or 4-hexyl-hexylresorcinol Substantial reduction of brown- ing PEREZ-GAGO et al. (2006) Apple “Fuji” slic- es Ascorbic acid and citric acid 20% decrease of the respira- tion rate; shelf-life extension to 2 weeks. LEE et al. (2003) Apple slices Carbohydrate/lipid bilayer film Carbohydrate/lipid bilay- er film Water loss reduction WONG et al. (1994) Fresh-cut “Fuji” apple Tapioca starch/de- colorized hsian-tsao leaf gum Cinnamon oil Reduction of microbial growth, respiration rate, CO 2 and eth- ylene production PAN et al. (2013) Fresh-cut Taap- tijaan rose apple Konjac glucomannan Pineapple fruit extract Increase of total phenols; in- hibi-tion of PPO and POD activities. SUPAPVANICH et al. (2012) Fresh-cut apple slices Pullulan Pullulan; glutathione and chitooligosaccharides D e l ay o f t i s s u e s o fte n i n g, inhibition of microbial growth, decrease of weight loss and respiration rate. WU and CHEN (2013) Fresh-cut apple slices Chitosan Ascorbic acid and CaCl2 Delay of enzymatic browning and tissue softening HAIPING et al. (2011) Ital. J. Food Sci., vol. 27 - 2015 13 table 2a - Application of edible coating on fresh-cut fruits and vegetables. Food product Coating Composition Main results References Sliced kiwifruit “Hai- ward” Aloe vera Aloe vera Reduced O 2 consumption and CO 2 production; reduc- tion of microbial spoilage BENÍTEZ et al. (2013) Sliced mango Fresh-cut mango Chitosan Alginate and gellan Chitosan Ascorbic acid Reduction of water loss Increase of Vitamin C BICO et al. (2009) ROBLES-SÁNCHEZ et al. (2013) Fresh-cut mango (pre-treated with citric acid dipping) Sliced banana Cassava starch-edi- ble coating Carrageenan Cassava starch-edible coating Carrageenan Reduction of weight loss and respiration rate; better maintenance of colour char- acteristics Reduction of water loss CHIUMARELLI et al. (2010, 2011) BICO et al. (2009) Cantaloupe melon cube Soy protein Alginate Soy protein, glycerol, malic acid, lactic acid Malic acid and essential oils of cinnamon, pal- marosa and lemongrass Good sensory character- istics Microbiological shelf-life ex- tension. ESWARANANDAM et al. (2006) RAYBAUDI-MASSILIA et al. (2008) Fresh-cut papaya Alginate and gellan Chitosan and pectin Ascorbic acid Microencapsulated anti-micro- bial complex (beta-cyclodex- trin and trans-cinnamaldehyde) Preservation of the natu- ral ascorbic acid content in papaya Shelf-life extension to 15 days; reduction of vitamin C and total carotenoid con- tent loss MANTILLA et al. (2013); SIPAHI et al. (2013) Fresh-cut apple, pa- paya, pear, melon Alginate Alginate Shelf-life extension to 15 days FONTES et al. (2007); TAPIA et al. (2007); OMS-OLIU et al. (2008) Fresh-cut pineapple, fresh-cut melon Multilayered Sodium algi- nate coating Microencapsulated antimicro- bial complex (beta-cyclodex- trin and trans-cinnamaldehyde) Prevention of water loss FONTES et al. (2007); TAPIA et al. (2007); OMS-OLIU et al. (2008) Fresh-cut pineapple; Fresh-cut strawber- ries Cassava starch-edi- ble coating Calcium lactate/ potassium sorbate Reduction of weight loss Reduction of respiration rate BIERHALS et al. (2011) GARCIA et al. (2010) bIodegrAdAble PAckAgIng And MInIMAlly Processed FruIts And VegetAbles Fruits and vegetables are living organisms which continue to respire and transpire after harvesting, being characterized by a respira- tion rate; respiration and transpiration rates of fresh fruits and vegetables are often good indi- cators of their storage life; the higher the rate, the shorter the shelf-life (Floros, 1993). More- over, the shelf-life of fresh-cut products is limit- ed by microbiological deterioration and in order to reduce the effects of microbiological, chemi- cal and physical events, it is possible to act on processing or, more usually, on packaging. the packaging operation should allow to establish inside the packaging an optimal atmosphere for the best preservation of the product. gen- erally, low and elevated atmospheres, together with low storage temperature, reduce the prod- uct respiration rate limiting, in this way, loss- es in fresh weight (WAtAdA et al., 1996). the at- mosphere that is established is the resultant of oxygen and carbon dioxide permeation through the walls of the packaging and of respiration 14 Ital. J. Food Sci., vol. 27 - 2015 table 2b - Application of edible coating on fresh-cut fruits and vegetables. Food product Coating Composition Main results References Minimally processed pummel Cassava or rice starch Cassava or rice starch Lower weight loss of 4.8– 7.7% than the control KERD- CHOECHUEN et al. (2011) Fresh-cut peach Pectin Essential oil from cinna- mon leaves Reduction of bacterial growth; better antioxi- dant status AYALA-ZAVALA et al. (2013) Pear slices Chitosan Carboxymethyl chitosan Sodium chlorite Increase of PPO activity Inhibition of PPO activity XIAO et al. (2011) Fresh-cut pineapple Alginate Lemongrass oil Reduction of microbial growth AZARAKHSH et al. (2014) Fresh-cut brocco- li, garlic Fresh-cut broccoli Chitosan Chitosan Chitosan Bioactive compounds (bee pollen, ethanol- i c ex t ra c t o f p ro p o - lis, pomegranatedried extract,resveratrol)/es- sential oils (tea tree, rosemary, clove, orega- num, lemon aloe vera calendula) Reduction of meso- philic and psychrotrophic counts; inhi- bition of the yellowing and opening florets of fresh-cut broccoli Better control of microorgan- isms (E. coli and L. monocy- togenes); good sensory at- tributes MOREIRA et al. (2011) GERALDINE et al. (2008) ALVAREZ et al. (2013) Fresh-cut carrots Tapioca starch/decolor- ized hsian-tsao leaf gum Active calcium-alginate coating loaded with sil- lver montmori-llonite (Ag MMTT) nanoparticles Cinnamon oil High biocidal effects No beneficial effect on con- trolling the meso- phyles aer- obics and psychrophiles Good control of dehy- dra- tion and microbial spoilage; of shelf-life extension to about 70 days, with respect to the uncoated samples LAI et al. (2013) COSTA et al. (2012) by the cells, until reaching an equilibrium con- dition aimed to slow the senescence and avoid sensorial defects to the packaged product. ei- ther high co 2 or low o 2 concentrations could in- directly induce off-flavours by stimulating the growth of homo- and hetero-fermentative bac- teria and yeast, which produce organic acids, ethanol and volatile esters (cArlIn et al., 1989; kAkIoMenou et al., 1996). therefore, a proper combination of product characteristics and film permeability, which is a fundamental character- istic of the packaging materials, results in the evolution of an appropriate atmosphere with- in packages (sMItH et al., 1987). Moreover, the packaged food actually interacts with the pack- aging material, changing the initial mechanical and barrier properties of the packaging materi- als (Petersen et al., 1999). In alternative to the traditional polymeric ma- terials, biodegradable films and coatings could be used. In fact, studies and experiments re- lating to possible applications of biodegradable materials, possibly combined with coating tech- nique, to minimally processed fruits and vegeta- bles are not lacking. results obtained by using biodegradable films for samples of Iceberg let- tuce are interesting: the film that is traditional- ly used to package fresh-cut salads is the bi-ori- ented polypropylene, which is associated with a level of senescence, linked to the metabolic ac- tivity of the vegetable, which is always higher than that achieved by salads packaged in bio- degradable film. so, the potential application of biopolymers for the packaging of fresh-cut let- tuce is justified (del nobIle et al., 2008). Also the rate of quality loss of minimally processed grapes in relationship with packaging film bar- rier properties has been assessed (del nobIle et al., 2009a). In earlier work, del nobIle et al. (2008b) investigated the influence of posthar- vest treatments (ethanol, chlorinated water and hot water) on the quality loss kinetics of fresh- ly processed grapes packaged in biodegradable films. the results suggested that ethanol is the Ital. J. Food Sci., vol. 27 - 2015 15 best solution to preserve the microbial stability of the fresh produce without affecting its respi- ration rate to any great extent. based on these results, clusters of table grapes (Vitis vinifera cv. Italia) were treated in ethanol solution pri- or to packaging in different bags made of two types of commercially available films (a multi- layer film obtained by laminating nylon and a polyolefin layer (nP); an oriented polypropylene film (oPP)) and in three biodegradable polyester- based films (nVt-100, nVt-50, nVt-35). results suggest that the respiratory activity of packed minimally processed produce is the main rea- son for its quality loss during storage. In fact, the best results in terms of grape quality were obtained using grapes with lower respiratory activity and high barrier films, such as nP and nVt-100. From a sensory point of view, no un- desirable after-taste developed within the fruit, when the grapes were packaged in the thicker film (nP and nVt-100). Also PlA has been tested for fresh-cut fruits and vegetables packaging; the coating of PlA silicon oxide (siox) improved the barrier oxy- gen and water vapor properties (PeelMAn et al., 2013). In particular, the use of PlA containers with lids and pouches composed of Vc999 bi- opack PlA films coated with a barrier of pure siox to preserve quality of fresh-cut pears af- ter 9 days of storage in comparison with con- ventional polyethylene Pe material, has been investigated. the results showed that color and firmness color of fresh-cut pears is better main- tained with biodegradable packaging materials (krAsnoVA et al., 2013) biodegradable materials do not always ful- fill the physiological requirements of the specif- ic fruit and/or vegetable packaged in them: in fact, poor moisture barrier properties, linked to the hydrophilic character that marks most of the bio-based-materials, is sometimes responsible for higher percentages of weight loss in prod- ucts, such as zucchini (lucerA et al., 2010), artichokes (del nobIle et al., 2009b) lampas- cioni (Muscari comosum) (conte et al., 2009c) and melon (conte et al., 2009b). often in several experiments, the technique of coating is used as a pretreatment to improve the performance of biodegradable materials and its effects on product quality. the coating treat- ment, containing sodium alginates, has been more effective than the dipping in delaying the metabolic activity associated to respiration rate in samples of lampascioni, subsequently pack- aged in ntV2, a film based biodegradable poly- ester (conte et al., 2009c). Moreover, the brown- ing process decreased, as well as, the microbial growth, since the availability of oxygen on the surface of the product was reduced. the same type of coating was also applied to fresh-cut ar- tichokes (del nobIle et al., 2009 b): also in this case, the coating together with packaging in ntV2 film seems to represent the better strat- egy to preserve the quality of artichokes, also from a microbiological point of view. Interest- ing results also came from a study of fresh-cut cactus-pear: the shelf life of the minimally pro- cessed fruit, coated with an alginate and then packed with monolayer film (based on a blend of biodegradable polyesters), was prolonged to about 13 days, corresponding to an shelf-life in- crease of about 40%, compared to the control sample (untreated sample); on the contrary, pro- duce immersion into either agar or fish protein strongly reduced the shelf life, most probably due to water migration from the surrounding hydro-gel to the fresh-cut produce (del nobI- le et al., 2009 c). Also PlA has been tested for fresh-cut fruits and vegetables packaging; the coating of PlA silicon oxide (siox) improved the barrier oxy- gene and water vapor properties (PeelMAn et al., 2013). In particular, the use of PlA contain- ers with lids and pouches composed of Vc999 biopack PlA films coated with a barrier of pure siox to preserve quality of fresh-cut pears af- ter 9 days of storage in comparison with con- ventional polyethylene Pe material, has been investigated. the results showed that color and firmness color of fresh-cut pears is better main- tained with biodegradable packaging materials (krAsnoVA et al., 2013) PlA is also been used in combination with sil- ver; silver ions have been incorporated into poly- lactic film, in order to evaluate the silver-infused PlA films for inactivation of salmonella and fe- line calicivirus in vitro and on fresh-cut vegeta- bles (MArtÍnez-AbAd et al., 2013). the results showed that in vitro the antibacterial and anti- viral activity is more efficient than on food sam- ples. Anyway, in lettuce samples incubated a 4°c at 6 days of storage, 4 log cFu of salmonel- la was inactivated for film with 0.1% wt of silver ions and no viral infection has been found in the same conditions (MArtÍnez-AbAd et al., 2013). the results of the case studies on biodegrad- able packaging applied to fresh-cut fruits and vegetables and in some cases combined with ed- ible coating are summarized in table 3. conclusIons Foodstuffs are dynamic systems with a limited shelf-life and specific requirements in terms of packaging. In order to ensure the highest stan- dards of product quality, the right combination of product characteristics and packaging film is the basis for the development of appropriate storage conditions. this work focuses on the potential applica- tions of biodegradable packaging and edible coating for minimally processed foods. the re- sults highlight how the biodegradable films may have a more or less advantageous performance in relation to the physiological characteristics of 16 Ital. J. Food Sci., vol. 27 - 2015 table 3 - Application and combination of biopolymer with coating for fresh-cut fruits and vegetables packaging. Food product Biopackaging Property of materials Main results Reference Iceberg lettuce Polyester-based biodegradable film Good gas barrier prop- erties Shelf-life extension DEL NOBILE et al. (2008) Table grape (Vitis vinifera) Polyester-based biodegrad- able film /nylon and polyole- fin layer High gas barrier Good microbiological stability; good sensory characteristics DEL NOBILE et al. (2009) (ethanol pre-treatment be- fore packaging) Zucchini (Cucurbi- ta pepo) Biodegradable co-extruded polyesters High permeability to wa- ter vapor High percentage of weight loss LUCERA et al. (2010) Artichoke Biodegradable monolay- er film based on a blend of biodegradable polyesters Permeability to water vapor High percentage of weight loss; good microbiological stability DEL NOBILE et al.( 2009) Coating with sodium algi- nate (pre-treatment before packaging) Barrier to water vapour Shelf-life extension (200%) low water loss Lampascioni (Muscari comosum) Polyester-based biodegradable film High permeability to wa- ter vapor High percentage of weight loss CONTE et al. (2009) Coating with sodium algi- nate (pre-treatment before packaging) Barrier to water vapour and oxygen Lower water loss; low micro- bial growth. reduced brown- ing process Cactus pear Fresh-cut pears (Pyrus communis) Monolayer film, based on a blend of biodegradable polyesters High permeability to wa- ter vapour High percentage of weight loss. DEL NOBILE et al. (2009) KRASNOVA et al. (2013) Coating with alginates (pre-treatment before pack- aging) PLA films coated with a barrier of pure silicon ox- ide (SiOx) Barrier to water vapour and other agents Improved barrier prop- erties Shelf-life extension to about 13 days Better maintenance of color an firmness with respect to con- ventional PE packaging Melon Blend of biodegradable pol- yester High permeability to wa- ter vapor High percentage of weight loss CONTE et al. (2009) complex matrices, such as fruit and vegetables, characterized by an active metabolism which sig- nificantly affects their conservation. certainly, biopolymers fulfill the environmental require- ments but they have some limitations in terms of performance, like thermal resistance, barri- er and mechanical properties. better results can be achieved by the combined use of biodegrad- able packagings with edible coatings. the use of edible films and coatings represents an environmentally-friendly technology that of- fers substantial advantages for shelf-life prolon- gation of many food products, including fruits and vegetables. the development of new natu- ral edible films and coatings with either inher- ent microbicidal activity or the addition of anti- fungal ingredients (food preservatives, essential oils, antagonistic microorganisms, etc.) to im- prove the quality of fresh-cut fruits and vegeta- bles is a technological challenge for the industry and a very active field of research worldwide. ed- ible coatings can keep product characteristics, such as texture and hydration intact, and they can provide significant fruit senescence retarda- tion. Moreover, they serve as a carrier for a wide range of food additives, including anti-browning or antimicrobial agents. new challenges should focus on the devel- opment of tailor-made coatings, containing the most appropriate film forming constituents and active ingredients for fresh and minimally pro- cessed fruits and vegetables, according to spe- cific industrial needs. new trends have shown that enrichment of biodegradable materials with silver-montmorillonite nanoparticles may be a promising technique. undoubtedly, biodegradation offers an at- tractive route to environmental waste manage- ment. However, the actual application of these packaging solutions to food is still limited, due to the high cost of raw materials and the small- scale production. In the future, when the quan- Ital. J. 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