Bibliographic review

Polysaccharide-based films as biodegradable coatings in fruits postharvest

Yuliem Mederos-Torres^{1  *} 
http://orcid.org/0000-0001-5795-4348

Patricia Bernabé-Galloway² 
http://orcid.org/0000-0002-4588-8133

Miguel Ángel Ramírez-Arrebato³ 
http://orcid.org/0000-0002-2730-7358

¹Instituto Nacional de Ciencias Agrícolas (INCA), carretera San José-Tapaste, km 3½, Gaveta Postal 1, San José de las Lajas, Mayabeque, Cuba. CP 32 700

²Instituto de Ciencia y Tecnología de Materiales, Laboratorio de Polímeros. Calle Zapata s/n, entre G y Carlitos Aguirre, Vedado, La Habana, Cuba. CP 10400

³Unidad Científico Tecnológica de Base "Los Palacios". Km 1½ carretera La Francia, Los Palacios, Pinar del Río, Cuba. CP 22900

ABSTRACT

The postharvest preservation of fruits and vegetables is a vital issue due to the large losses generated during its handling in the domestic market and exportation. Microbiological and physiological deterioration, inadequate collection process, the use of inappropriate packaging and insufficient transportation routes are key factors for these losses. The use of biodegradable films and coatings is an alternative to decrease these losses. Biodegradable films and coatings are generally either composed of carbohydrates proteins and lipids individually or combined. These coatings constitute a semipermeable barrier to water vapor, oxygen (O₂) and carbon dioxide (CO₂) between fruits and the surrounding environment. In general, they can slow down the senescence process and microbial growth on the surface of the fruits, which allows quality preservation and facilitates their distribution and commercialization. Due to the potential and importance that this type of technology currently presents in our national context, this review was carried out taking into account the main components used in the formation of these materials, the practical application in fruits and vegetables, and the principal characterization procedures of these biodegradable films and coatings.

Key words: chitosan; pectin; starch; proteins; lipids

INTRODUCTION

The conservation of the fruits in the postharvest is a matter of vital importance for the commercialization and distribution of the same. Post-harvest losses of fruit and vegetable products rise from 5 to 25 % in developed countries, and from 20 to 50 % in developing countries ¹. Generally, these losses are due to microbiological and physiological deterioration, to an inadequate collection process, to the use of inadequate packaging and insufficient transportation routes. To mitigate these problems, a group of alternatives have been developed such as storage at low temperatures ², the application of gamma and ultraviolet radiation ³, the application of biological controls ⁴, the use of controlled atmospheres and plastic packaging ⁵, the use of aminoethoxyvinylglycine ⁵ and 1-methyl chloropropene to delay fruit ripening ². Also, the use of biodegradable films and coatings ⁶, among others.

In particular, the development of biodegradable films and coatings for fresh and processed food products has gained momentum in recent times. This is because this technology is environmentally friendly and can improve the quality of food, its biosecurity and stability. These characteristics are achieved by providing a semipermeable barrier to water vapor, dioxygen (O₂) and carbon dioxide (CO₂) between the fruits and the surrounding atmosphere. This technology serves as a protective barrier by reducing metabolic processes such as respiration, delaying the senescence process and microbial growth on the surface of the fruit, which allows preserving quality and facilitating the distribution and marketing of these ^7).

Biodegradable coatings must be toxic free and safe for health, they must require simple technology for their elaboration and protect the fruits from any physical, chemical or mechanical action. At the same time, they must be transparent and cannot be detected during consumption ⁸. Polysaccharides are the main components present in edible films and coatings. Among them, we can mention high and low methoxyl pectins ⁹, chitosan ¹⁰, cellulose and its derivatives ¹¹, algae extracts (alginate ¹², carrageenan, agar ¹³ and gum arabic ¹⁴, among others. Other compounds used are lipids such as beeswax ¹⁵, waxes extracted from candelilla plants ¹⁶⁾ and laurel ¹⁷, as well as proteins, both from animal sources (casein ¹⁸, gelatin ¹⁹⁾ as vegetables (wheat gluten ²⁰, zein ²¹, soy, peanuts and rice ¹²), among others.

These compounds can be part of the films individually or combined with each other. Furthermore, they can be linked to additives that improve the antioxidant, antimicrobial and mechanical properties of coatings to extend their shelf life and reduce the risk of pathogen growth on the food surface ²². Taking into account that these films have proven to be effective in terms of food safety and environmental contamination, they could be a viable alternative in the industrial sector. Cuba is a country rich in fruit and vegetable products that are destined for both domestic consumption and export, so having technologies that allow them to extend their useful life is vitally important. For this reason, the objective of this work is to approach the art state on biodegradable films research based on polysaccharides. They are used as a post-harvest coating, their main sources of production, characteristics, analyzes that are carried out and the main fruit and vegetable products in which they are used, in order to develop a line for obtaining biodegradable coatings from Cuban raw materials.

Edible films and coatings

A biodegradable coating can be defined as a continuous, thin, transparent matrix that is created around a food, generally by immersing it in a coating-forming solution, in order to preserve its quality and also serve as a packaging ⁸. A biodegradable film is in the form of a solid sheet and is applied by wrapping the product in it ²³. Active biodegradable coatings maintain quality and extend the shelf life of fresh fruits and vegetables, as well as prevent microbial spoilage ¹⁰. The deterioration in the fruits is mainly caused because they are biologically active and transpiration (loss of humidity), respiration (gas exchange), maturation and other biochemical processes occur in them ²⁴. Biodegradable coatings reduce moisture and solute migration. Its application offers a plausible solution to obtain fresh, nutritious and edible products. They serve as semi-permeable barriers to gases and water vapor, reducing respiration and water loss. Furthermore, they delay deterioration and senescence in a similar way to modified atmospheres ²⁵.

Biodegradable coatings must meet certain functional requirements that allow them to control or lessen the causes of alteration in the foods to be coated (Figure 1) ^26-31. However, when coating a fruit or vegetable to delay moisture loss, it is necessary there be a certain permeability to O₂ and CO₂ to avoid anaerobic respiration that could induce physiological disorders and a rapid loss of quality and shelf life of themselves ^23).

Figure 1 Characteristics, advantages and disadvantages of coatings and biodegradable films 

Main components of biodegradable coatings and films

The main components of biodegradable films and coatings are carbohydrates (sugars and polysaccharides), proteins and lipids. Polysaccharides are macromolecules made up of monosaccharides linked by glycosidic bonds and their hydrolysis produces a large number of molecules of one or more simple sugars (monosaccharides) or their derivatives ³².

Polysaccharides and proteins are polymers that form cohesive molecular networks due to a high interaction between their molecules, which gives them good mechanical properties and a barrier to O₂ and CO₂ gases, thus slowing down the respiration and aging of many fruits and vegetables ⁷. These compounds have been widely used in food processing, nanotechnology, medicine, biotechnology, and agriculture ³³. Its use in biodegradable coatings has been extensively documented as shown in Table 1. These compounds give the films and coatings hardness, sharpness, compactness, viscosity and adhesiveness ¹³. The sources of obtaining the polysaccharides are very varied; they can be of plant origin (pectins, cellulose, starch, alginate, carrageenan, among others) and animal (chitin) ¹².

Table 1 Clasificación de los materiales que forman las películas o recubrimientos biodegradables 

Carbohydrates	Protein	Lipids
Animal source: Chitosan ^10. Vegetable source: High and low methoxyl pectins ^9. Cellulose and its derivatives ^11. Starch ^18 Gum arabic ^14. Algae extracts (alginate ^34, carrageenan ^35, and agar ^13.	Animal sources: casein ^18, gelatin ^19. Plant sources: zein (corn ^21) soy, gluten (wheat) ^20, peanuts, rice ^13	Animal Source: Beeswax ^15 Vegetable sources: Candelilla wax ^17 Laurel wax ^17. Carnauba wax ^36 Resins and fatty acids: stearic acid ^37, palmitic, lauric, oleic ^38 and coconut butter ^39

Chitosan

Chitosan is one of the most widely used polysaccharides in obtaining biodegradable coatings. Its origin is from chitin, the second most abundant polysaccharide in nature after cellulose. It is a semi-synthetic polymer that is obtained by deacetylation of chitin, which is mainly found in the exoskeleton of crustaceans, although it is also found in a smaller proportion in the wings of some insects, and in the cell wall of fungi, algae and others ¹⁰. From a chemical point of view, it is a copolymer composed of units of N-glucosamine (D-GlcN), N-Acetyl glucosamine (D-GlcNAc) randomly distributed, and linked by β-(1-4) glycosidic bonds in a structure rigid unbranched. Chitosan is presented as a potential material to obtain biodegradable coatings, mainly due to its capacity to form films, its non-toxic nature, its antimicrobial activity ⁴⁰, as well as its biodegrabability and biocompatibility. This polymer is recognized to have gas barrier properties, thus ensuring decreased senescence by preventing respiration and perspiration ¹⁰. Chitosan is generally dissolved in acetic acid, although lactic acid has also been used for these purposes ⁴¹.

The incorporation of an additive such as calcium gluconate to the chitosan-based coating increases the nutritional value of the fruit, due to an increase in its calcium content ³⁸. Calcium plays an essential role in the structural maintenance of the membranes and the cell wall. The crosslinking of calcium with free carboxyl groups in adjacent polygalacturonate chains present in the mid lamella of the plant cell wall contributes to adhesion and cohesion between cells ⁴². That is why a treatment with calcium can increase the stability of the cell wall and improve resistance to the enzymes secreted by phytopathogenic fungi, while the coating with chitosan reduces respiration, delaying the maturation process and the progressive deterioration of the product fruits of senescence.

Pectin

Another polysaccharide used in edible coatings is pectin. Pectins are located mainly in the middle lamella of the primary cell wall of plants, where they contribute to the adhesion between the cells of the plant parenchyma and the strength of their tissues ⁴³. It is mainly made up of two regions, a uronic region; Extensive and regular, made up of galacturonic acid units linked by α-(1,4)-type bonds, which may be partially methylated, and the second composed mainly of rhamnose that carry neutral sugar side chains ⁴⁴.

Pectins are used extensively in processed foods because of their gelling properties ⁴⁵. Under certain conditions, they are capable of forming gels, a characteristic for which they are considered an important additive in hams, jellies, jams, as well as in the clothing industry. Agricultural sources of pectin are currently underutilized, even though pectin is a potentially important food ingredient available and abundant in agricultural waste. Precisely, its pharmaceutical application and the additional nutritional benefit in a wide variety of food products increase the interest in this polysaccharide ³⁹.

Studies on pectin films date mostly from the 1930 to 1950 ⁴⁶. These studies focused on derivatized pectins and the use of polyvalent cations such as calcium. The study of films from low methoxyl pectins (<11 %) shows that the tensile strength decreases with the increase of the methoxyl groups ⁴⁶. The physical characteristics of the gel are the consequence of the formation of a three-dimensional network or of the cross-linking between the polymer molecules ⁴⁷. Low methoxyl pectins, derived by controlled deesterification, form gels in the presence of calcium ions and can be used to develop biodegradable films. Pectin is highly hydrophilic, since it is composed of at least 17 types of monosaccharides, among which D-galacturonic acid is the most abundant, followed by D-galactose or L-arabinose, and covalently linked to each other ⁴⁸. Hence, the water vapor permeability (PVA) of pectin films is quite high, in the same order of magnitude as that of cellophane and other carbohydrate-based films ⁵¹. Thermomechanical, microstructural and viscoelastic properties of pectin-based films, such as the mixture of pectin and starch, concluding that they are highly resistant ⁴⁹

Starch

Starch is another of the carbohydrates used in the development of biodegradable coatings individually or in combination; it is widely used due to its abundance and low cost. Starch is a reserve polysaccharide made from amylose and amylopectin. Starch-based coatings are transparent, colorless, and odorless and have low oxygen permeability ⁵⁰. Starch has also been combined with carrageenan to form highly resistant biodegradable films ⁵¹.

Chitosan and pectin based coatings

The antimicrobial character in biodegradable coatings is a highly desired attribute. In the case of chitosan, antimicrobial activity has been related to the ability of this polymer to cause severe damage at the cellular level to the mycelium of fungi treated with this polymer ⁵². However, it has been enhanced when combined with the lactoperoxidase enzyme system in the preservation of mango ⁴¹. Lactoperoxidase is an excellent system to combat pathogenic microorganisms and has a broad antimicrobial spectrum. The combination of 1 % chitosan with the lactoperoxidase enzyme system is effective against microbial contamination and allows delaying fruit ripening without altering its quality ⁴¹. Zinc II and Cerium IV complex with chitosan have also been used to preserve Chinese jujube fruit, extend the shelf life of the fruit and reduce residues of organophosphate pesticides. Zinc is one of the most important essential micrometallic elements in the human body. It is an essential component in a significant number of proteins and is essential for the stability of catalytic functions. Cerium ions have good antibiotic capacity ⁵³. In turn, chitosan has been combined with lemongrass essential oils to preserve pepper against anthracnose ⁵⁴, and thyme, cinnamon and clove to preserve papaya against P. digitatum and C fungi. gloesosporioides where it promotes greater mycelial inhibition in in vitro studies at a chitosan concentration of 0.5 and 1 % ³⁸.

In the case of pectin-based coatings, essential oils of cinnamon ^15), lemon, orange ⁹⁾ and cinnamaldehyde nanoemulsions ⁵⁵ have been incorporated, among others. Another example is the modification of the surface of polypropylene (PP) films by multilayers of chitosan/pectin. In these films, chitosan forms a polyelectrolyte complex with pectin, which enables the formation of a stable multilayer structure on the surface of the PP film, with the consequent formation of much better antimicrobial films that can be used to manufacture excellent packaging materials for post-harvest crop protection ⁵⁶.

In general, polysaccharide-based coatings such as chitosan and pectin constitute a poor moisture barrier due to the hydrophilicity they present. For this reason, many works have been aimed at combining these polymers with lipids, resins and fatty acids (Table 1), with the aim of regulating the hydrophilic-lipophilic balance ³⁹. Lipids are characterized by being hydrophobic, have excellent moisture barrier properties, although their lack of cohesiveness and structural integrity result in poor mechanical properties, leading to the formation of brittle coatings. Lipids reduce perspiration, dehydration, abrasion in subsequent handling, and can improve the gloss and appearance of many foods ⁸.

Other additives: proteins and plasticizers

Proteins are another component used in biodegradable coatings. Among the proteins used for the production of these, casein, zein and gelatin stand out among others. Casein has gained prominence in the development of coatings because it is commercially available, has the ability to act as an emulsifier, is water soluble ⁵⁷ and produces transparent and thermally stable coatings ¹⁸. The combination of casein and starch together with glycerol and barbatimón extract has been used in the preservation of guava. This coating lengthens the shelf life of guavas, reduces weight loss and firmness ¹⁸.

Another example is the formation of biodegradable films from chitosan-bound quinoa protein, forming resistant films without the use of plasticizers, the addition of sunflower essential oil, improves water vapor permeability as a result of interactions hydrophobic ⁵⁸. Zein is a storage protein found in corn kernels. This protein has the characteristic of preventing oxidation and the development of bad odors due to its excellent gas barrier properties against oxygen and carbon dioxide ⁵⁹. Gelatin films have effective properties as a gas barrier against oxygen and carbon dioxide ⁶⁰.

Plasticizers are non-volatile, high-boiling point substances that, when added to another material, change the physical or mechanical properties of this material ³⁹. Polyols like sorbitol and glycerol effectively plasticize for their ability to reduce internal hydrogen bonding while increasing intermolecular spacing. These plasticizers decrease intermolecular forces along the polymer chain, increasing the flexibility of the film while decreasing its barrier properties ⁶¹. Plasticizers have also been used in obtaining biodegradable coatings, such as sorbitol ⁶¹, glycerol ⁶², polyethylene glycol ³⁷ and papaya puree ⁵⁵.

The proportion in which the components are found in the coatings is important. A study on the influence of the amount of pectin and plasticizer on the mechanical properties of the fruit revealed that an increase pectin for and a decrease in the amount of plasticizer increases the tensile strength and modulus of elasticity, while the elongation at break increases with increasing concentration of both ⁶¹. Similarly, an increase in the concentration of pectin and plasticizer affects PVA, due to the hydrophilic nature of both compounds. However, the combination with a lipid like beeswax lowers PVA. At low concentrations, the added lipid increases hydrophobicity, thus decreasing the permeability of the film. At higher concentrations, lipids could result in larger globules during the drying stage in obtaining the film, contribute to the interruption of the continuous structure of the films, and consequently to a higher PVA ⁶³. The studies of coatings formed from methylcellulose, stearic acid and polyethylene glycol carried out by an emulsion method, reveal that the increase in the volume of stearic acid up to 22 % causes a decrease in PVA ³⁷. However, the increase in the volume of stearic acid above 22 % leads to an increase in PVA, attributed to inadequate filling of the empty volume inside the stearic acid crystals by the methylcellulose matrix, which favors migration of moisture. On the other hand, the increase in PVA in pectin and sorbitol films at high concentrations of both may perhaps be due to a greater heterogeneity because of the distribution of lipid globules (number of populations) within the pectin matrix ⁶¹.

Practical applications of biodegradable coatings and films

Fruits and vegetables are an invaluable source of vitamins and minerals in the daily diet of humans. An adequate conservation of these, allows extending the shelf life in the post-harvest. Biodegradable coatings and films have been used with great success in the preservation of guava (Psidium guajava L.) ⁶⁴, papaya (Carica papaya L.) ⁶⁵, mango (Mangifera indica L.) ⁶⁶, mandarin orange (Citrus reticula L.) ⁶⁷, strawberry (Fragaria ananassa Duch) ⁵⁸, tomato (Lycopersicon esculentum Mill.) ⁶⁸, bell pepper (Capsicum annuum L.) ⁵⁴ and the cucumber (Cucumis sativus L.) ²⁷, among others.

The practical application of coatings in most cases reduces weight loss and ripening rate, and increases the shelf life of the fruits (Table 2). In the ripening process during storage, a series of physical and biochemical changes occur that vary depending on the type of fruit ⁹. Among the changes, we can find the modification of the color through the alteration in the content of chlorophylls, carotenoids and the accumulation of flavonoids. In turn, the modification of the product texture to the alteration of the cell turgor and the structure of the cell wall by metabolism. As well as, the modification of carbohydrates, organic acids and volatile compounds, which affect the nutritional quality, flavor and aroma of the fruit. Last but not least, the increased susceptibility to attack by opportunistic pathogens that are associated with loss of cell wall integrity ²⁴.

It is recognized that during the maturation process the total soluble solids (TSS) are increased due to the respiration process ⁹, during which the degradation of carbohydrates and organic acids (ascorbic, citric and malic) occurs due to the use of these as a substrate in the breathing process ⁵⁴. The increase in the TSS content and the reduction in the measurable acidity are indicators of the maturation process ⁶⁹.

In the case of tomato, pectin-based coatings increase the retention of ascorbic acid, measurable acidity and total sugars during storage compared to the control ⁶⁵. These results are positive since they indicate a delay in maturation due to the action of the coating, since they limit oxygen permeability, reducing the oxidation of ascorbic acid, and limiting the use of citric acid as a substrate in the respiration process.

The chitosan-salicylic acid combination has been studied in the conservation of cucumber at low temperatures of 2 °C ²⁷. These study shows that the combination reduces the damage caused by the low temperatures on the surface of the cucumber and that the combined action exceeds that of the components individually. Chitosan-salicylic acid also reduces weight loss and respiration rate, causes increases in malondialdehyde content and electrolyte leakage, and maintains a higher content of TSS, chlorophyll, and ascorbic acid.

Table 2 Biodegradable coatings and films applied to the fruits 

Application	Composition of biodegradable films and coatings.	Function	Reference
Guava	Chitosan 1 %, acetic acid	Extension of the useful life of the fruit. Reduces weight loss and firmness. Delays the maturation process by inhibiting respiration rates.	^64
	Casein, starch, glycerol and extract of barbatimón		^18
Papaya	Chitosan 2 %, Acetic Acid 0.5 %, Tween 80.		^70
Tomato	Chitosan 0,25 %		^68
	Pectin 3 %, water		^65
	Chitosan 1 %, zeolite (Ø=35-45 μm), lactic acid, Tween 80	Delays fruit ripening, but is a poor barrier to weight loss	^71
Mango	Acetato de quitosana 20 %	Reduction of the incidence of anthracnose. Delays the maturation process.	^66
Cucumber	Chitosan Acetate 20 %		^72
	Highly methoxylated pectin 2 %, beeswax, sorbitol and water	Extension of the useful life of the fruit, reduction of respiration rates. Reduces weight loss and firmness	^27
Mandarine	Pectin 8 % and water	Extension of the useful life of the fruit. Reduces weight loss and firmness	^67
Pepper	Chitosan 1 %, NaOH 1M, Lemongrass Essential Oil 0.5 %, Tween 80	Reducción de la incidencia de antracnosis. Retrasa el proceso de maduración.	^54
Strawberry	Pectin 1 %, glycerol 0.02 %, lemon essential oil 1 and 0.5 %	Extension of the useful life of the fruit. Reduces weight loss and firmness	^9
	Quinoa protein 0.1 % -quitosan 2 % in citric acid-sunflower essential oil 2.9 %	Extension of the useful life of the fruit. Reduces weight loss and firmness. Reduces mold and yeast growth	^58

Both zein and gelatin have been successfully tested in post-harvest preservation of mango ⁵⁹. Both proteins combined with glycerol positively affect weight loss, TSS, titratable acidity, pH, total sugar content, and carotenoid content. Additionally, they maintain the content of total phenols and ascorbic acid at high levels compared to the control ⁵⁹.

When carrying out practical applications of the coatings, it is necessary to take into account the concentration of the carbohydrate or the component in question. A chitosan concentration of 1.5 % inhibits the growth of the fungi during the storage period in the preservation of the pumpkin fruit, while the increase above 2 % leads to inadequate maturation ^70).

It concludes, the application of biodegradable coatings to fruits and fruit and vegetable products is extremely important because they extend shelf life, allowing for better transportation and marketing of these. This type of technology in our country is highly attractive for the preservation of exportable fruits such as pineapple, mango and avocado, as well as for the internal marketing of the wide variety of fruits and vegetables that are produced in our domestic market and for supplying our tourist facilities.

Main physico-chemical characteristics to be evaluated in edible films and coatings

Among the physical characteristics to be evaluated in the coatings are the thickness of the films from the measurement with a micrometer ¹⁶. The determination of the viscosity allows studying the flow properties at different concentrations of the polymers. Generally, for this analysis, a rheometer is used to measure the viscosity and the viscoelastic properties of solutions at different concentrations of the polymers ⁶¹. Film surface studies are performed by scanning electron microscopy ⁷³ or atomic force ⁷⁴, and Fourier transform infrared spectroscopy (FTIR) allows identifying structural changes made in the polymers from the changes in their characteristic absorption bands ¹⁰. These techniques allow for a structural analysis of the film surface that provides information on the composition of the film.

Another analysis to be performed is the permeability to water vapor. This analysis is extremely important in edible coatings because a low permeability slows down the loss of weight in the fruit. Gravimetric methods have been developed for this, among which is the ASTM E96-93 ⁷⁵ standard. This procedure is based on the prior drying of the membrane or film in a waterproof container and the subsequent contact of this container with magnesium nitrate to maintain the relative humidity of the films at 53 %. Later they are stored in desiccators maintaining humidity relative (RH) in 0 % with the help of a drying agent such as calcium chloride at 25 °C. The water vapor transmission rate divided by the difference in vapor pressure across the film constitutes the permeability of the film ⁶¹. The permeability multiplied by the thickness of the film is the transmission to water vapor ⁷⁵.

Another procedure is ASTM E96/E96M-10 ⁷⁶ with some modifications, where the 3 cm diameter membranes, previously stored for at least 72 hours in a desiccator, are placed in containers containing silica gel inside and they are hermetically sealed, taking care that only the membrane is exposed to water vapor. The containers in a desiccator are weighed and placed containing a saturated solution of KCl. It provides a constant water activity equal to 0.8434 at 25 °C. Subsequently, the desiccator is in a chamber at constant temperature placed. The containers are on an analytical balance every 24 hours removed and weighed. The calculation of PVA is made from the slope of the graph of the variation in mass over time using (Equation 1). The experiment is considered concluded when no increase in the weight of the containers is observed.

$PVA=\frac{∆m}{∆t}xA$ (1)

Where $\frac{∆m}{∆t}$ is the slope of the weight graph over time and A is the effective area of the membrane in contact with the water vapors ⁷⁷. Tensile strength (τ) is one of the mechanical properties that are performed to verify the resistance of the films. It is carried out in a texture analyzer ¹⁶. In the analysis the samples are stretched to rupture, the resulting force is divided by the cross section of the film, and τ is expressed in MPa. Furthermore, the stretching capacity to rupture (CE) is calculated in percentage, with (Equation 2), where Li and Lf are the initial and final lengths of the films, expressed in millimeters (mm) ¹⁶⁾ .

$CE=\left(\frac{L_f-L_i}{L_i}\right)*100$ (2)

CONCLUSIONS

• Biodegradable coatings are of great importance in the post-harvest handling of fruit and vegetable products. Generally, for its formation, the use of polymers from various natural sources such as pectin, chitosan, starch, cellulose derivatives, among others, combined with lipids, emulsifiers and plasticizers is used.

• The great variety of polysaccharides obtained from various plant and animal sources, as well as the combination of these with other additives that allow improving the characteristics of these coatings, extending the possibility of infinite combinations of these compounds, with a view to achieving the best results.

• The use of biodegradable coatings contributes to increasing the shelf life of fruit and vegetable products, which constitutes a useful and promising technology in the conservation of fruits in the post-harvest of our country.

BIBLIOGRAFÍA

1. Gustavsson J, Cederberg C, Sonesson U, Emanuelsson A. The methodology of the FAO study: "Global Food Losses and Food Waste -extent, causes and prevention"-FAO, 2011. [Internet]. The Swedish Institute for Food and Biotechnology; 2013 p. 70. Report No.: 857. Available from: http://www.diva-portal.org/smash/get/diva2:944159/FULLTEXT01.pdf

2. Guzmán T, Cuenca K, Tacuri E. Caracterización de la poscosecha de la mora de castilla (Rubus glaucus) tratada con 1-metilciclopropeno. Revista Ciencias Técnicas Agropecuarias. 2018;27(1):66-75.

3. Khan QU, Mohammadzai I, Shah Z, Ihsanullah, Khattak TN, Noreen H, et al. Effect of Gamma Irradiation on Nutrients and Shelf Life of Peach (Prunus persical) Stored at Ambient Temperature. The Open Conference Proceedings Journal. 2018;9(1). doi:10.2174/2210289201809010008

4. Sivakumar D, Zeeman K, Korsten L. Effect of a biocontrol agent (Bacillus subtilis) and modified atmosphere packaging on postharvest decay control and quality retention of litchi during storage. Phytoparasitica. 2007;35(5):507-18. doi:10.1007/BF03020609

5. Ozturk B, Uzun S, Karakaya O. Combined effects of aminoethoxyvinylglycine and MAP on the fruit quality of kiwifruit during cold storage and shelf life. Scientia Horticulturae. 2019;251:209-14. doi:10.1016/j.scienta.2019.03.034

6. Núñez-Castellano K, Castellano G, Ramírez-Méndez R, Sindoni M, Marin RC. Efecto del cloruro de calcio y una cubierta plástica sobre la conservación de las propiedades organolépticas de la fresa (Fragaria X Ananassa Duch). Revista Iberoamericana de Tecnología Postcosecha. 2012;13(1):21-30.

7. Dickinson E. Hydrocolloids as emulsifiers and emulsion stabilizers. Food Hydrocolloids. 2009;23(6):1473-82. doi:10.1016/j.foodhyd.2008.08.005

8. Fernández D, Bautista S, Fernández D, Ocampo A, García A, Falcón A. Películas y recubrimientos comestibles: una alternativa favorable en la conservación poscosecha de frutas y hortalizas. Revista Ciencias Técnicas Agropecuarias. 2015;24(3):52-7.

9. Abdi S, Roein Z, Erfanimoghadam J, Aziznia S. Application of Pectin Coating Containing Essential Oil for Increasing Quality of Strawberry Fruit. Journal of Postharvest Technology. 2017;05(4):83-94.

10. Nisha V, Monisha C, Ragunathan R, Johney J. Use of Chitosan as Edible Coating on Fruits and in Micro biological Activity - An Ecofriendly Approach. International Journal of Pharmaceutical Science Invention. 2016;5(8):7-14.

11. Arnon H, Zaitsev Y, Porat R, Poverenov E. Effects of carboxymethyl cellulose and chitosan bilayer edible coating on postharvest quality of citrus fruit. Postharvest Biology and Technology. 2014;87:21-6. doi:10.1016/j.postharvbio.2013.08.007

12. Paula GA, Benevides NMB, Cunha AP, de Oliveira AV, Pinto AMB, Morais JPS, et al. Development and characterization of edible films from mixtures of ?-carrageenan, ?-carrageenan, and alginate. Food Hydrocolloids. 2015;47:140-5. doi:10.1016/j.foodhyd.2015.01.004

13. Mellinas C, Valdés A, Ramos M, Burgos N, Garrigós M del C, Jiménez A. Active edible films: Current state and future trends. Journal of Applied Polymer Science. 2016;133(2). doi:10.1002/app.42631

14. Etemadipoor R, Ramezanian A, Dastjerdi AM, Shamili M. The potential of gum arabic enriched with cinnamon essential oil for improving the qualitative characteristics and storability of guava (Psidium guajava L.) fruit. Scientia Horticulturae. 2019;251:101-7. doi:10.1016/j.scienta.2019.03.021

15. Moalemiyan M, Ramaswamy HS. Quality Retention and Shelf-life Extension in Mediterranean Cucumbers Coated with a Pectin-based Film. Journal of Food Research. 2012;1(3):159-68. doi:10.5539/jfr.v1n3p159

16. Lozano-Grande MA, Valle-Guadarrama S, Aguirre-Mandujano E, Lobato-Calleros CSO, Huelitl-Palacios F, Lozano-Grande MA, et al. Películas basadas en emulsiones de pectina de frutos de tejocote (Crataegus spp.) y cera de candelilla: caracterización y aplicación en Pleurotus ostreatus. Agrociencia. 2016;50(7):849-66.

17. Andrade J, Acosta D, Bucheli M, Luna GC. Elaboración y evaluación de un recubrimiento comestible para la conservación postcosecha del tomate de árbol Cyphomandra betacea Cav. Sendt. Revista de Ciencias Agrícolas. 2013;30(2):60-72.

18. Remor A, Cardoso D, Caetano J, Botin C, Ferreira L. Conservação de goiabas com revestimentos comestíveis de amido e caseína com extrato de barbatimão. Revista Engenharia na Agricultura. 2018;26(4):295-305. doi:10.13083/reveng.v26i4.928

19. Matta Fakhouria F, Martelli SM, Caon T, Velasco JI, Innocentini Mei LH. Edible films and coatings based on starch/gelatin: Film properties and effect of coatings on quality of refrigerated Red Crimson grapes. Postharvest Biology and Technology. 2015;109:57-64. doi:10.1016/j.postharvbio.2015.05.015

20. Tanada-Palmu PS, Grosso CRF. Effect of edible wheat gluten-based films and coatings on refrigerated strawberry (Fragaria ananassa) quality. Postharvest Biology and Technology. 2005;36(2):199-208. doi:10.1016/j.postharvbio.2004.12.003

21. Escamilla-García M, Calderón-Domínguez G, Chanona-Pérez JJ, Farrera-Rebollo RR, Andraca-Adame JA, Arzate-Vázquez I, et al. Physical and structural characterisation of zein and chitosan edible films using nanotechnology tools. International Journal of Biological Macromolecules. 2013;61:196-203. doi:10.1016/j.ijbiomac.2013.06.051

22. Pranoto Y, Salokhe VM, Rakshit SK. Physical and antibacterial properties of alginate-based edible film incorporated with garlic oil. Food Research International. 2005;38(3):267-72. doi:10.1016/j.foodres.2004.04.009

23. Falguera V, Quintero JP, Jiménez A, Muñoz JA, Ibarz A. Edible films and coatings: Structures, active functions and trends in their use. Trends in Food Science & Technology. 2011;22(6):292-303. doi:10.1016/j.tifs.2011.02.004

24. Martínez-González ME, Balois-Morales R, Alia-Tejacal I, Cortes-Cruz MA, Palomino-Hermosillo YA, López-Gúzman GG. Poscosecha de frutos: maduración y cambios bioquímicos. Revista mexicana de ciencias agrícolas. 2017;8(spe19):4075-87. doi:10.29312/remexca.v0i19.674

25. Xing Y, Li X, Xu Q, Jiang Y, Yun J, Li W. Effects of chitosan-based coating and modified atmosphere packaging (MAP) on browning and shelf life of fresh-cut lotus root (Nelumbo nucifera Gaerth). Innovative Food Science & Emerging Technologies. 2010;11(4):684-9. doi:10.1016/j.ifset.2010.07.006

26. Okcu Z, Yavuz Y, Kerse S. Edible Film and Coating Applications in Fruits and Vegetables. Alinteri Zirai Bilimler Dergisi. 2018;33(2):221-6. doi:10.28955/alinterizbd.368362

27. Zhang Y, Zhang M, Yang H. Postharvest chitosan-g-salicylic acid application alleviates chilling injury and preserves cucumber fruit quality during cold storage. Food Chemistry. 2015;174:558-63. doi:10.1016/j.foodchem.2014.11.106

28. Salinas-Roca B, Soliva-Fortuny R, Welti-Chanes J, Martín-Belloso O. Combined effect of pulsed light, edible coating and malic acid dipping to improve fresh-cut mango safety and quality. Food Control. 2016;66:190-7. doi:10.1016/j.foodcont.2016.02.005

29. Guerreiro AC, Gago CML, Faleiro ML, Miguel MGC, Antunes MDC. The effect of edible coatings on the nutritional quality of 'Bravo de Esmolfe' fresh-cut apple through shelf-life. LWT. 2017;75:210-9. doi:10.1016/j.lwt.2016.08.052

30. Pagliarulo C, Sansone F, Moccia S, Russo GL, Aquino RP, Salvatore P, et al. Preservation of strawberries with an antifungal edible coating using peony extracts in chitosan. Food and Bioprocess Technology. 2016;9(11):1951-60. doi:10.1007/s11947-016-1779-x

31. Badawy MEI, Rabea EI, El-Nouby MAM, Ismail RIA, Taktak NEM. Strawberry shelf life, composition, and enzymes activity in response to edible chitosan coatings. International Journal of Fruit Science. 2017;17(2):117-36. doi:10.1080/15538362.2016.1219290

32. Griffin RW. Química orgánica moderna. Reverte; 1981. 610 p.

33. Parvin N, Kader MA, Huque R, Molla ME, Khan MA. Extension of shelf-life of tomato using irradiated chitosan and its physical and biochemical characteristics. International Letters of Natural Sciences. 2017;67:16-23. doi:10.18052/www.scipress.com/ILNS.67.16

34. Rozo G, Gómez D, Rozo C. Efecto de una biopelícula de alginato en la conservación de cebolla larga (Allium fistulosum L.). Vitae. 2016;23(1):419-23.

35. Esguerra EB, Ocfemia GS, Pamulaklakin JA (Philippines ULB. Postharvest behaviour of `carabao' mango fruits coated with chitosan and carrageenan. En: Philippine Journal of Crop Science (Philippines) [Internet]. 2000 [cited 24/10/2019]. Available from: http://agris.fao.org/agris-search/search.do?recordID=PH2001100580

36. Singh S, Khemariya P, Rai A, Rai AC, Koley TK, Singh B. Carnauba wax-based edible coating enhances shelf-life and retain quality of eggplant (Solanum melongena) fruits. LWT - Food Science and Technology. 2016;74:420-6. doi:10.1016/j.lwt.2016.08.004

37. Sapru V, Labuza TP. Dispersed phase concentration effect on water vapor permeability in composite methyl cellulose-stearic acid edible films. Journal of Food Processing and Preservation. 1994;18(5):359-68. doi:10.1111/j.1745-4549.1994.tb00259.x

38. Hernández López M, Guillén Sánchez J, Bautista Baños S, Guillén Sánchez D. Evaluación de películas biodegradables en el control de hongos postcosecha de la papaya. Cultivos Tropicales. 2018;39(1):52-60.

39. Maftoon Azad N. Evaluation of edible films and coatings for extending the postharvest shelf life of avocado. 2006 [cited 22/10/2019]; Available from:http://digitool.library.mcgill.ca/R/?func=dbin-jump-full&object_id=102678&local_base=GEN01-MCG02

40. Varun TK, Senani S, Jayapal N, Chikkerur J, Roy S, Tekulapally VB, et al. Extraction of chitosan and its oligomers from shrimp shell waste, their characterization and antimicrobial effect. Veterinary World. 2017;10(2):170-5. doi:10.14202/vetworld.2017.170-175

41. Cissé M, Polidori J, Montet D, Loiseau G, Ducamp-Collin MN. Preservation of mango quality by using functional chitosan-lactoperoxidase systems coatings. Postharvest Biology and Technology. 2015;101:10-4. doi:10.1016/j.postharvbio.2014.11.003

42. Bakshi P, Masoodi FA, Chauhan GS, Shah TA. Role of calcium in post-harvest life of temperate fruits: a review [Internet]. Journal of Food Science and Technology Mysore. 2005 [cited 22/10/2019]. Available from:https://eurekamag.com/research/004/306/004306809.php

43. Ridley BL, O'Neill MA, Mohnen D. Pectins: structure, biosynthesis, and oligogalacturonide-related signaling. Phytochemistry. 2001;57(6):929-67. doi:10.1016/s0031-9422(01)00113-3

44. Inngjerdingen M, Inngjerdingen KT, Patel TR, Allen S, Chen X, Rolstad B, et al. Pectic polysaccharides from Biophytum petersianum Klotzsch, and their activation of macrophages and dendritic cells. Glycobiology. 2008;18(12):1074-84. doi:10.1093/glycob/cwn090

45. Stephen AM. Other Plant Polysaccharides. En: Aspinall GO, editor. The Polysaccharides [Internet]. Academic Press; 1983 [cited 23/10/2019]. p. 97-193. doi:10.1016/B978-0-12-065602-8.50008-X

46. Schultz TH, Miers JC, Owens HS, Maclay WD. Permeability of Pectinate Films to Water Vapor. The Journal of Physical and Colloid Chemistry. 1949;53(9):1320-30. doi:10.1021/j150474a002

47. Guo J-H, Skinner GW, Harcum WW, Barnum PE. Pharmaceutical applications of naturally occurring water-soluble polymers. Pharmaceutical Science & Technology Today. 1998;1(6):254-61. doi:10.1016/S1461-5347(98)00072-8

48. Yapo BM, Robert C, Etienne I, Wathelet B, Paquot M. Effect of extraction conditions on the yield, purity and surface properties of sugar beet pulp pectin extracts. Food Chemistry. 2007;100(4):1356-64. doi:10.1016/j.foodchem.2005.12.012

49. Fishman ML, Coffin DR, Konstance RP, Onwulata CI. Extrusion of pectin/starch blends plasticized with glycerol. Carbohydrate Polymers. 2000;41(4):317-25. doi:10.1016/S0144-8617(99)00117-4

50. Yan Q, Hou H, Guo P, Dong H. Effects of extrusion and glycerol content on properties of oxidized and acetylated corn starch-based films. Carbohydrate Polymers. 2012;87(1):707-12. doi:10.1016/j.carbpol.2011.08.048

51. Thakur R, Saberi B, Pristijono P, Golding J, Stathopoulos C, Scarlett C, et al. Characterization of rice starch-?-carrageenan biodegradable edible film. Effect of stearic acid on the film properties. International Journal of Biological Macromolecules. 2016;93:952-60. doi:10.1016/j.ijbiomac.2016.09.053

52. Bautista-Baños S, Hernández-Lauzardo AN, Velázquez-del Valle MG, Hernández-López M, Ait Barka E, Bosquez-Molina E, et al. Chitosan as a potential natural compound to control pre and postharvest diseases of horticultural commodities. Crop Protection. 2006;25(2):108-18. doi:10.1016/j.cropro.2005.03.010

53. Wu H, Wang D, Shi J, Xue S, Gao M. Effect of the Complex of Zinc(II) and Cerium(IV) with Chitosan on the Preservation Quality and Degradation of Organophosphorus Pesticides in Chinese Jujube (Zizyphus jujuba Mill. cv. Dongzao). Journal of Agricultural and Food Chemistry. 2010;58(9):5757-62. doi:10.1021/jf100537k

54. Ali A, Noh NM, Mustafa MA. Antimicrobial activity of chitosan enriched with lemongrass oil against anthracnose of bell pepper. Food Packaging and Shelf Life. 2015;3:56-61. doi:10.1016/j.fpsl.2014.10.003

55. Otoni CG, Moura MR de, Aouada FA, Camilloto GP, Cruz RS, Lorevice MV, et al. Antimicrobial and physical-mechanical properties of pectin/papaya puree/cinnamaldehyde nanoemulsion edible composite films. Food Hydrocolloids. 2014;41:188-94. doi:10.1016/j.foodhyd.2014.04.013

56. Elsabee MZ, Abdou ES, Nagy KSA, Eweis M. Surface modification of polypropylene films by chitosan and chitosan/pectin multilayer. Carbohydrate Polymers. 2008;71(2):187-95. doi:10.1016/j.carbpol.2007.05.022

57. Shendurse A, Gopikrishna G, Patel A, Pandya A. Milk protein based edible films and coatings-preparation, properties and food applications. Journal of Nutritional Health & Food Engineering [Internet]. 2018 [cited 10/10/2019];8(2). doi:10.15406/jnhfe.2018.08.00273

58. Valenzuela C, Tapia C, López L, Bunger A, Escalona V, Abugoch L. Effect of edible quinoa protein-chitosan based films on refrigerated strawberry (Fragaria×ananassa) quality. Electronic Journal of Biotechnology. 2015;18(6):406-11. doi:10.1016/j.ejbt.2015.09.001

59. Gol NB, Rao TVR. Influence of zein and gelatin coatings on the postharvest quality and shelf life extension of mango (Mangifera indica L.). Fruits. 2014;69(2):101-15. doi:10.1051/fruits/2014002

60. Jiang M, Liu S, Du X, Wang Y. Physical properties and internal microstructures of films made from catfish skin gelatin and triacetin mixtures. Food Hydrocolloids. 2010;24(1):105-10. doi:10.1016/j.foodhyd.2009.08.011

61. Maftoonazad N, Ramaswamy HS, Marcotte M. Evaluation of factors affecting barrier, mechanical and optical properties of pectin-based films using response surface methodology. Journal of Food Process Engineering. 2007;30:539-63.

62. Maftoonazad N, Ramaswamy HS. Application and Evaluation of a Pectin-Based Edible Coating Process for Quality Change Kinetics and Shelf-Life Extension of Lime Fruit (Citrus aurantifolium). Coatings. 2019;9(5):285. doi:10.3390/coatings9050285

63. Kamper SL, Fennema O. Water Vapor Permeability of Edible Bilayer Films. Journal of Food Science. 1984;49(6):1478-81. doi:10.1111/j.1365-2621.1984.tb12825.x

64. Krishna KR, Rao DVS. Effect of chitosan coating on the physiochemical characteristics of guava (Psidium Guajava L.) fruits during storage at room temperature. Indian Journal of Science and Technology. 2014;7(5):554-558-558. doi:10.17485/ijst/2014/v7i5/49467

65. Felix ED, Mahendran T. Active packaging of green mature tomatoes with pectin coating to extend the shelf life. Journal of Science-Eastern University. 2009;6(1):1-9.

66. Mulkay-Vitón T. Efecto de sales de quitosano en la calidad poscosecha del mango Tommy Atkins. Cultivos Tropicales. 2017;38(3):135-41.

67. Placido GR, Silva RM, Silva M a. P, Furtado DC, Santos MG, Caliari M, et al. Use of pectin in the postharvest conservation of tangerine. African Journal of Biotechnology [Internet]. 2014 [cited 23/10/2019];13(52). doi:10.5897/AJB2014.14111

68. Sucharitha KV, Beulah AM, Ravikiran K. Effect of chitosan coating on storage stability of tomatoes (Lycopersicon esculentum Mill). International Food Research Journal. 2018;25(1):93-9.

69. Mali S, Grossmann MVE. Effects of yam starch films on storability and quality of fresh strawberries (Fragaria ananassa). Journal of Agricultural and Food Chemistry. 2003;51(24):7005-11. doi:10.1021/jf034241c

70. Ali A, Muda Muhammad MT, Sijam K, Siddiqui Y. Effect of chitosan coatings on the physicochemical characteristics of Eksotika II papaya (Carica papaya L.) fruit during cold storage. Food Chemistry. 2011;124:620-6. doi:10.1016/j.foodchem.2010.06.085

71. García M, Casariego A, Díaz R, Roblejo L. Effect of edible chitosan/zeolite coating on tomatoes quality during refrigerated storage. Emirates Journal of Food and Agriculture. 2014;238-46. doi:10.9755/ejfa.v26i3.16620

72. Adetunji CO, Fadiji AE, Aboyeji OO. Effect of chitosan coating combined Aloe vera gel on cucumber (Cucumis sativa L.) post-harvest quality during ambient storage. Journal of Emerging Trends in Engineering and Applied Sciences. 2014;5(6):391-7.

73. Liu L, Jin T, Liu C-K, Hicks K, Mohanty AK, Bhardwaj R, et al. A preliminary study on antimicrobial edible films from pectin and other food hydrocolloids by extrusion method. Journal of Natural Fibers. 2008;5(4):366-82. doi:10.1080/15440470802460643

74. Elsabee M, Abdou E, Nagy K, Eweis M. Surface modification of polypropylene films by chitosan and chitosan/pectin multilayer. Carbohydrate Polymers. 2008;71:187-195. doi:10.1016/j.carbpol.2007.05.022

75. ASTM. Standard test methods for water-vapor transmission of materials [Internet]. Philadelphia: E96-93, 1993 [cited 26/10/2019]. Available from:https://users.encs.concordia.ca/~raojw/crd/reference/reference000277.html

76. ASTM E96. Test Methods for Water Vapor Transmission of Materials [Internet]. West Conshohocken: E96M-10, 2010 [cited 29/10/2019]. doi:10.1520/E0096_E0096M-10

77. Bernabé-Galloway P. Estudio físico-químico del complejo polielectrolitoquitosana-pectina: Obtención y caracterización de sus membranas. [Tesis Doctoral]. [La Habana, Cuba.]: Universidad de la Habana; 2015. 102 p.

Received: January 08, 2020; Accepted: March 16, 2020

^*Author for correspondence: [e-mail]