1. Introduction

Packaging is the science, art and technology of enclosing or protecting products for distribution, storage, sale and use. There are several packaging materials present in the market such as plastic, paper, cardboard, PET and also new technologies such as Active, intelligent vacuum, aseptic packaging, etc. Edible packaging is one of them. According to Food Production Daily, a new type of edible food packaging that does not affect the environment and that can be eaten with food that is inside the package has been invented. Harvard Professor and biomedical engineer, David Edwards, developed edible packaging, also called ‘future of food packaging’ Zoe [1]. Edible packaging is categorised into films, coating, pouches and sheets. The edible coating (EC) is prepared directly on the food, whereas edible films (EF) and layers having thickness 10 mm or less than 254 μm and more than 254 μm, respectively, are separately prepared, and then food is packed in it, in the pouches form or placed between the food layers [2, 3]. As packaging material contains various additives (flavourings, colourings, sweeteners) [4]. Lipid, carbohydrates, protein (casein), tomato skin are used to make edible packaging [5]. In the recent year, use of edible film and coating is emphasised due to its function of food protection from negative environmental effect and also helps to increase shelf life of food. Materials from which EF and EC are made are decided by their functions. Edible packaging materials have exceptional properties such as barrier and mechanical properties, enhance sensory properties and optical properties, making them attractive alternative for food packaging [2]. Based on the type of food and storage conditions, components of edible packaging are selected [6]. Currently, edible packaging gives replacement to other packaging because it inhibits loss of gas, aroma and moisture of the packed food. Krochta and De [3] added nano-fillers to film and coating for improved quality and acceptability. Various methods are used to manufacture film. Casting method is generally used. By comparing EF with synthetic packaging, EF has benefits over it because EF is eaten with contained food as a component of same food, and if not eaten, it has biodegradability [4, 7, 8]. EF satisfies industry requirements by keeping quality of food, fulfils consumer desires and reduces environmental pollution [9].

2. Need of edible packaging

Food packaging is very crucial for various purposes such as labelling, protecting the contained food, caring for the food, measuring, attracting the consumers, etc. Mostly, plastic is used as food packaging material. Globally, factories produce 400 MT of plastic per year approximately [10]. About 12.7 metric tons of plastic waste enters the ocean every year which affects the life of marine lives ([11] https://www.condorferries.co.uk/plastic-in-the-ocean-statistics). From total plastic waste about 79% is dumped in land, 12% incinerated and 9% is recycled. This plastic waste can take up to 400 years to break down in the landfill harming animal life, polluting cities or devastating landfills [12]. Dumped plastic affects (i.e. reduces) the moisture and oxygen transfer rate of soil and deteriorates the quality of the land. Figure 1 shows state-wise plastic waste generation of India. It seems that Maharashtra state produces plastic waste in higher percentage. To overwhelm the harmful environmental effects as well as health effects of plastic and improvement of food, many companies are trying to replace excess plastic packaging with such packaging material which will be degraded, which does not produce much waste and does not have any negative effect on human health, food as well as an environment like edible packaging materials which do not produce packaging waste, and if may consumer throw the edible packaging, then it is degraded which required the same period as its contained food.

Figure 1.
State-wise plastic waste generation. Source: https://www.business-standard.com/article/markets/plastic-ban-maharashtra-gujarat-among-top-indian-plastic-waste-producers-122070400736_1.html.

(https://cpcb.nic.in/uploads/plasticwaste/Annual_Report_2019-20_PWM.pdf)

2.1 Impact of edible packaging on environment

Some packaging material has exclusive use, and that may be thrown away after it’s used rather than recycled or reused [13]. Such plastic waste goes into rather in landfill, incinerate or in ocean which polluted the soil (land), air or water, respectively. As consumer demanded for the plastic-free food due to its negative health effect, companies are affording to get solution on it. The best way to contend the plastic in food packaging and also feasible to get zero plastic waste from food industry is by encouraging the customer to eat food along with its wrapper [14]. But this is only possible when that wrapper is GRAS for eating. Edible packaging is the finest solution to the plastic for reducing the waste which affects the environment and health of consumer. Nowadays, companies produce edible packaging in the form of pouches, wrappers, sachets, containers, plates, etc.

Commonly, edible packaging can be eaten, and in some amount, it is not eaten by consumers, but there is no need to reject the waste or no need to recycle it because edible packaging has biodegradability as it is composed of edible and environmentally safe components which biodegrade in less period of time [15]. The demand of edible packaging could rise by 6.9% yearly till the 2024, and market worth could be almost $2 billion, informed by global research firm TMR (Transparency Market Research) [14].

2.2 History

Edible coating and films have been used for centuries to protect foods. The history of packaging is given in Table 1, the idea is derived from the natural protective coating on some foods such as the skin of fruits and vegetables [16]. In the twelfth and thirteenth centuries, China used a wax coating to decrease water loss, on lemon and oranges. In 1856, the first cellulose EF was developed, and in 1907, phenol-formaldehyde (Bakelite) resin was used. This was the starting point of a series of developments and inventions giving birth to a great range of packaging materials that nowadays are employed [17].

Year	Country	Findings
Twelfth century	China	Waxes were applied to oranges and lemons
Fifteenth century	Japan	Yuba (1st free-standing edible film) from soymilk
Sixteenth century	England	Food products were coated with lard (control moisture loss)
1930s	US	Hot-melt paraffin waxes were have been used to coat citrus fruits
1950	—	Carnauba wax and oil–water emulsion—for coating fresh fruits and veggies
Twentieth century	—	Casing for sausages and chocolate coating for nuts and fruits

Table 1.

History of packaging.

Source: Robertson [16].

2.3 Classification of edible films and coating

Edible film and coating are classified based on their raw material sources, i.e. protein, polysaccharide, lipids and composites. They possess various functions such as retarding loss of moisture and volatile compounds, acting as a barrier for fat and oil and having a high selective gas permeability ratio of CO₂/O₂ as compared with conventional packaging [18].

2.3.1 Protein-based edible films

Technological and functional properties of protein may improve by changing the structure of protein for preparing edible film and coating [19]. Protein-based edible films have additional stimulating mechanical and barrier properties than polysaccharides [20]. They have the capacity to slab the gases due to its structure in which hydrogen-bonded network is packed tightly [21]. Food quality is declined mostly due to oxidation of lipid which can be preserved by using protein-based edible film having ability to inhibit oxygen permeation [22]. Many protein materials have been tried: collagen, corn zein, wheat gluten, soy protein isolates, fish proteins, ovalbumin, whey protein isolate, casein, etc [23]. In addition to their nutritional value, milk protein such as casein has several key physical characteristics for active performance in edible films such as emulsification and water solubility [24]. Sesame seed protein was mostly used in manufacturing of edible film [25]. Protein-based edible films transfer various additives such as plasticisers, antioxidants, essential oil, antimicrobial agents, etc. The diffusion of additives components from the surface to the interior is controlled by keeping the film on the food surface [15]. Nuts, cashew nuts and beans require special packaging which is fulfilled by the protein-based film [26].

2.3.1.1 Collagen

Collagen is a protein obtained from animal which is rich in glycine, proline and hydroxyproline and hydrophilic in nature [27]. Among all protein-based edible film, collagen is most commercial and successfully used film. For production of homogeneous surface film, high concentration of hydrolysed collagen is used [28]. Collagen powder and fibres were revealed to be suitable for the production of the bio-composite film in which fibres act as fillers and boost the effect [29].

2.3.1.2 Gelatin

Partial acid or alkali hydrolysis of collagen is used to produce gelatin at high temperature in the presence of water. Due to unique properties of gelatin, it is widely used in cosmetics, food, pharmaceuticals, industry [30]. Edible film obtained from gelatin has impermeability to CO₂ and flexibility due to its random arrangement of polypeptide chain in water solution [31]. Also gelatin possesses antioxidant property. Antimicrobial activity of gelatin is studied by Gomez-Guillen et al. [32]. But still, the relation between antimicrobial activity and peptide characteristics of gelatin is not revealed. Edible packaging materials act as carriers for additives, gelatin is one the carriers which carries bioactive components [33]. Gelatin has advantages such as having ability of good film forming, low in price, non-toxicity, biodegradability and gas and oil resistance property but has poor thermal stability, water resistance and mechanical property [34]. Gomez-Guillen et al. [32] stated that formation of an active packaging and extending the functional properties of biodegradable films were only possible due to usage of natural antioxidants and antimicrobial compounds. Gelatin-based edible films have poor water vapour barrier property which can be overcome by adding surfactant, i.e. lecithin, to it [35].

2.3.1.3 Casein

Casein is a milk protein. It has coil-like structure [36] due to its structure, it can be processed easily. Casein is dissolved in water, but after being dipped in water, it gains about 50% weight [37]. By treating the aqueous solution of casein molecule, it forms films, which are flexible, tasteless and transparent [31, 33]. Casein film helps to retard migration of aroma, CO₂ and O₂, because casein contains more number of polar groups which have excellent adhering property [38]. By treating the casein film with buffer at its isoelectric point may enhance the mechanical property and reduce solubility of casein film [39]. Its drawback is its high price.

2.3.1.4 Gluten

Gluten has cohesiveness and elasticity which help to improve mechanical property of film [40]. Wheat gluten chiefly contains glutenins and gliadins, insoluble and soluble in aqueous alcohol, respectively [41]. Edible film made from wheat gluten has water barrier property [42], films are transparent, homogeneous and strong in nature [43]. By using high-pressure treatment to gluten film, the texture can be changed from smooth to rubber-like texture [44].

2.3.1.5 Zein

Zein is a maize protein which is hydrophobic in nature. It is by-product of the oil industry and bio-ethanol [45]. It can be used in manufacturing of edible film, coating and pouches [22]. It is mostly used in confectionery industry as a coating material [46]. It consists of protein which is alcohol-soluble [47]. Zein film is insoluble in water due to more number of non-polar amino acids in it, and it also helps to enhance its water vapour barrier property [48]. Concentration of alcohol in alcoholic zein solution may changes its physico-chemical properties which affect the film properties. For producing functional film from zein, antioxidant and antimicrobial compounds are added to zein coating and films [49]. By treating the zein film forming solution with gamma irradiation helps to enhance its appearance, water barrier property and colour [50]. Zein also combines with polysaccharide and other protein-based film such as glucomannan to improve its property [51]. Zein has ability to assemble by itself due to its hydrophobic and hydrophilic nature [52].

2.3.2 Polysaccharides based films

Polysaccharides such as starch, cellulose, chitin and chitosan, etc. are used for manufacturing of EF and EC. These ingredients are selected according to their suitability for mechanical strength, functional properties, etc. [19]. Polysaccharides are long chain of polymers which are made up of the repeating units of mono or disaccharides which are joined together by bonds called glycosidic bonds. In film characteristics and formation of it, H-bond has important role [15]. Polysaccharide films are made by coacervation process. During the coacervation process, the interaction of long-chain polymer gets changed, and this leads to forming new intermolecular hydrophilic and H-bonding after evaporating the solvent [2]. Polysaccharide coating has barrier properties such as O₂, oil, and aroma, but it has poor moisture barrier property [19]. And it also has good structural and strength ability. Use of polysaccharide edible film helps to delay ripening of fruit and vegetables and hence, increases its shelf life too [53].

2.3.2.1 Starch and derivatives

Starch is chiefly present in tubers, roots and seed of plants. Maize, wheat, potato, etc. are mainly used in the industry as starch source [54]. Starch produces semi-crystalline and amorphous layer due to formation of linear amylose and amylopectine (branched) by glucose polymerisation process [55]. Amylase is a polymer having linear structure which affects the amorphous nature of starch granules [54]. The concentration of amylase and amylopectine in starch is 20–30% and 70–80%, respectively [56]. Amylopectine and amylase are naturally present in granular form having size about 1–100 μm [54]. Mechanical property, barrier property of starch are dependent on it sources, concentration of amylase and amylopectine [57]. The application of starch-based films in food packaging is capable because of their environmental appeal, low cost, flexibility and transparency [58, 59]. Corn starch is a high amylose starch which is good source for formation of edible starch-based film. Film can be made from aqueous solution of starch and drying it for free-standing film [60]. Starch-based edible films help to prevent change in taste, appearance and flavour of contained food because film is tasteless, transparent and odourless in nature [57]. Starch film is highly hydrophilic in nature; due to this hydrophobicity, this film has poor barrier property for water. Main advantage of starch film is that it has excellent barrier property of CO₂ and O₂ [61].

2.3.2.2 Cellulose and derivatives

Cellulose is a common natural polymer present in nature. Repeating units of D-glucose linked by β-1,4, glycosidic bonds formed cellulose [62]. Cellulose has crystalline structure and tight packing of polymer chain which helps to resist salvation in aqueous media of edible film [60]. Due to the presence of intermolecular hydrogen bond cellulose having insolubility in water to overcome it, cellulose treated with alkali helps to make it soluble in water [56]. Etherification of cellulose results in the formation of water-soluble ethers: methyl cellulose (MC), carboxy methyl cellulose (CMC), hydroxyl propyl methyl cellulose (HPMC) and hydroxyl propyl cellulose (HPC), these form good-quality edible film [63]. Edible film based on cellulose derivatives has various characteristics/properties such as resistant to CO₂ and O₂, transparent, odourless, flexible, water soluble, etc. The hydrophobic:hydrophilic ratio of these film components decided its WVP [31, 64]. Šuput et al. [61] stated that MC is less hydrophilic in nature, hence has water barrier property. Gas and barrier property of cellulose is mainly dependent on its molecular weight [3]. Cellulose-based film acts as anti-rancidic agent due to the presence of large surface area and bipolar in structure [65].

2.3.2.3 Chitin and chitosan

Chitin is a biopolymer found in abundance in nature after cellulose [66]. It is found in cell wall of fungi, exoskeleton of crustaceans and many other biological materials [67]. Chitin contains poly (β-(1–4)-2-acetamido-d-glucose), and chitosan is obtained in the presence of alkalin from N-deacetylation [68]. Chitosan has anti-microbial property, which is very effective over yeast and mould, followed by Gram-positive and Gram-negative bacteria [15]. In mechanism of chitosan’s antimicrobial action, it results in harmful leakage of microbial proteinaceouse and intercellular components when positive charge chitosan and negative charge microbial cell membrane are interacted. Chitosan helps to prevent toxic production and microbial growth in product because it contains nearly amount of chelate trace metals [69]. From shrimp shells, chitin is obtained about 30%. In the process of obtaining chitin, shells are treated with NaoH at 85–110°C, and after obtaining it, for removing the CaCO₃, weak HCl solution was used at room temperature having about 1–10% concentration [70]. The physicochemical properties of Chitosan is dependent on the method used to obtained chitosan and used apparatuses [56]. It has been extensively used in films and coatings due to its ability to inhibit bacterial and fungal pathogens’ growth [71]. Santos et al. [72] stated that the antimicrobial property of chitosan film is enhanced by the availability of fatty acids in it. Chitosan forms coating which is semi-permeable in nature, which helps in delaying the ripening rate of fruits and vegetables by modifying the internal atmosphere. For obtaining tough, flexible and clear film, chitosan is made from aqueous solution [73, 74].

2.3.2.4 Alginate

Alginate is a sodium salt of alginic acid which has the ability to form film [70]. Alginate polysaccharide is chiefly extracted from seaweed which is in brown colour [75]. Divalent cations such as Mg, Mn, Ca, Fe are used for making alginate coating material which possess gelling character [76]. d-mannuronic acid (M) and l-gulurinic acid (G) are present in alginate having different proportion, arrangement [77], and it affects its physical property [78]. If the ratio of M/G is less than 1, it is means alginate contained higher amount of guluronic acid and hence formed strong bond while, if the ration of M/G is more than 1, it shows less amount of guluronic acid in alginate which may result in flexible structure [79]. The alginic acid obtained from different species of brown algar may contain different polymers such as mannumaric acid unit as main or guluronic acid as a main or both/partial mannuronic and gulurinic acid [80]. Alginate has colloidal nature with stabilising, thickening and suspending property which makes it suitable for film forming [81, 82]. Alginate-based edible film or coating has poor moisture barrier due to its hydrophilic nature [76], and also it has some desirable properties such as reduction in shrinkage and barrier for colour and odour [83]. Alginate forms coating/film by evaporation of solvent method which is done with or without gelation of it. For retarding dehydration and for protecting the oxidation of lipid in meat product, alginate coating/film is used [84]. For preparing the alginate, pieces of seaweed are dipped in sodium carbonate. After 2 h. slurry of sodium alginate was obtained which has glycellulose (undissolved part of seaweed). Obtained slurry was diluted with water and filtered through filter cloth, and then pressing is carried out. Then precipitation is done to obtain calcium alginate [81, 82].

2.3.3 Lipid-based film

From antique time, lipid was used as an edible coating for fruits. Mainly waxes were used for coating the citrus fruits [19]. The factors on which efficiency of lipid material are decided for formation of edible film or coating are its structure, nature of lipid used, its hydrophilic nature, its state and its interaction with other components of films, etc. [85]. To increase resistance of water penetration of film, lipids are generally combined with polysaccharides or proteins as multilayer coating [86]. Natural wax, surfactants and acetylated mono-glycerides are examples of lipid compounds which act as protective coating for fruits and vegetables [60]. Some examples of lipids, waxes and resins used for making edible film and coating are sunflower oil, cocoa butter, palm oil, etc.; paraffin, carnauba wax, candelilla wax, etc.; and tragacanth gum, gum arabic, etc., respectively [19].

2.3.3.1 Waxes and paraffin

The non-polar substances are produced by naturally as well as synthetically called as wax [61]. Waxes are soluble in organic solvent and insoluble in bulk water because waxes are hydrophobic in nature [87]. Wax micro-emulsion is manufactured by adding the water to molten wax in the presence of base and the fatty acids; this method is called as water-to-wax method. Present base plays the role of inverting the emulsion to wax-in-water [88]. Waxes are applied in thin layer on fruits. Thin layer on fruits is considered as edible. but if that layer is thick like on the cheese, it should be removed before eating. For getting humidity barrier, mostly used waxes are paraffin, bee wax and carnauba wax [60].

2.3.3.2 Shellac resins

The secretion of insect Lacciferalacca is called shellac resin which is the complex mixture of polymer that is aliphatic alicyclic hydroxyl acid. Shellac resin in not safe for eating, it is not permitted by GRAS. This is used only for adhesion and coating. And it is soluble in alkaline as well as alcohol solution. Hernandez [89] reported that the maximum use of resin is done in pharmaceutical industry than the food industry as a coating material. For coating citrus and other fruits, resin and its derivatives are used mainly as they have good barrier property which maintains their quality. But from this, coating gases are passed because coating has different gas permeability [90]. The internal environment of coated fruit with shellac and wood resin and wax coating are different, i.e. has high CO₂ and low O₂ and high in ethanol content and has low ethanol content, respectively [91, 92, 93]. Coating based on wood and shellac resin helps to enhance the prevalence of post-harvest pitting [94, 95].

2.3.4 Composite films

The film which is made from combinations of edible substances to make it stronger than before to overcome its drawbacks is called composite film [3]. The main motto of manufacturing composite film is utilisation of synergistic changes in film to overcome its individual lacks in some properties [19]. For making composite film, two different polymers are combined, such as lipid and protein; carbohydrates and protein; carbohydrates and lipid or/and synthetic as well as natural polymer. These composite coatings are applied in the form of solution, successive layer of film or coating, an emulsion, etc. [60].

2.3.4.1 Polysaccharide-protein edible coatings

The protein-polysaccharide-based composite film has good mechanical and water-vapour permeability property because interaction between protein-polysaccharide results in mono-phase film [18]. This composite film is proposed to be used as edible film for packaging in food industry [96]. Combination of carboxy methyl cellulose with soy protein improves the structure and properties of edible film [97]. By decreasing gas transfer rate in fruits, shelf life is increased; this is possible by using edible film made from collagen-galactomannan mixture [98].

2.3.4.2 Lipid-protein edible coatings

Protein has large number of polar group and is hydrophilic in nature. Due to its hydrophilicity, it has poor water vapour barrier, although it has good mechanical and oxygen property. Lipid is hydrophobic in nature. By combining these two makes film with stronger and good barrier properties as well as organoleptic property enhances and increases its market value [99]. Combined film also improves its water solubility [100]. To improve optical, mechanical and barrier properties of sodium caseinate–oleic acid–beeswax film, calcium caseinate is added to it [101].

2.4 Film/coating additives

Various material/substances are added to edible film to improve its properties such as mechanical, handling and structural and/or for improving active functions to coating or films [53]. For examples:

2.4.1 Plasticiser

For improving mechanical property of edible film, plasticisers are added to film solution during formation/manufacturing of film. Plasticiser has small molecular weight and is hydrophilic in nature. These small molecules are situated between their polymeric networks and make them stronger [2]. Commonly used plasticisers in edible packaging are polyols (sorbitol, glycerol), mono-, di- or oligosaccharides (glucose, sucrose), lipid and its derivatives (fatty acids, surfactants). Generally, the selection of plasticisers requires considering plasticiser’s compatibility, efficiency, permanence and economics [102].

2.4.2 Antimicrobials

Antimicrobial compounds are additives used to control biological deterioration and to inhibit the growth of microorganisms, including pathogenic microorganisms. Antimicrobial agent can be incorporated directly into the food during manufacturing or may be incorporated into food packaging materials [30]. There are several groups of antimicrobial compounds potentially incorporated into edible films, including chemical agents, natural extracts and probiotics [103]. Janjarasskul and Krochta [2] stated that for controlling growth of microorganisms, both natural and synthetic antimicrobial agents are added in edible film, and this is used as an alternative for it.

2.4.3 Natural extracts

2.4.3.1 Plant/spice extract

Different plant/spices, such as seeds, roots, bark, buds, flowers and leaves, are used to create the extracts. The phenolic chemicals, such as catechin, tannin, ferulic acid, caffeic acid, gallic acid and carvacrol, which are found in various portions of plants and spices, are mainly responsible for their antimicrobial properties [103]. Extraction of essential oil from plants (cinnamon, clove, onion, garlic, radish, etc.) comprises phenolic compounds such as phenolic acid and flavonoids which have biological activities such as antimicrobial and antioxidants [104].

2.4.3.2 Enzyme

The most employed antimicrobial enzyme is lysozyme which is made up of hydrophilic monopeptide chains [30]. Lysozyme is a nutraceutical and is produced from egg white, milk and blood [105]. It is shown to be more effective against Gram-positive bacteria. It separates N-acetylmuramic acid and N-acetylglucosamine bond of the peptidoglycan in the cell wall of bacteria [106]. Gram-negative bacteria have lipid-based outer cover to their cell walls; due to this, lysozyme is less effective on it [15]. By hydrolysing the peptidoglycan, lysozyme causes bacterial death by destroying the cell wall of bacteria [30].

2.4.3.3 Bacteriocins

Bacteriocins are macromolecules which contain protein and produced from the different varieties of bacteria and have different mode of action, chemical property. Bacteriocins are naturally occurring antimicrobial substances. They are small-molecular-weight peptides produced by microorganisms and effectively inhibit the growth of food spoilage bacteria, mainly Gram-positive bacteria [105]. The most employed antimicrobial bacteria are nisin and pediosin [103]. Antimicrobial efficiency of bacteriocins is influenced by their concentrations and number and species of microorganisms, using condition, interaction or inactivation by food elements and temperature and pH of the product [105].

2.4.3.4 Probiotics

Live bacteria known as probiotics can improve health when ingested in adequate quantities [107]. After 12 days of storage testing, Bekhit et al. [108] found that the film of hydroxyl propyl methylcellulose (HPMC) contains microencapsulation of Lactococcuslactis subsp. Lactis was successful in reducing the growth of Listeria monocytogenes by a five-log cycle when compared with control film. According to Beristain-Bauza et al. [109], whey protein isolate films containing Lactobacillus rhamnosus cell-free supernatant (12 or 18 mg/ml in film-forming solution) maintain inhibitory action against Gram-positive (Salmonella typhimurium and E. coli) and Gram-negative (E. coli) bacteria (L. monocytogenes and S. aureus). Probiotics can be incorporated into the edible polymer matrix to be used in the food packaging industry because of their safety, operative properties and useful qualities.

2.4.3.5 Emulsifiers

Emulsifier has both polarity and non-polarity; due to this, it acts as a surface active agent which has the ability to mix the two immiscible substances such as oil and water, by changing or modifying interfacial energy of these immiscible substances [2]. Emulsifiers are very important because they help to achieve proper and sufficient wetability to product which is essential for proper surface area and adhesion to the wrapping material [53]. Many proteins have emulsifying properties owing to their amphiphilic nature [2].

2.4.3.6 Chemical agents, organic acids and salts

Organic acids and their salts are mostly used as chemical antimicrobial agents for food products due to their efficacy and cost [110]. They are produced by chemical synthesis or chemical modification of natural acids [111]. The most widely used organic acids in film packaging are acetic acid, lactic acid, sorbic acid and citric acid. Films containing organic acids have been developed as a consequence of numerous scientific studies. For instance, Uranga et al. [112] reported that 20% (w/w) citric-acid-contained gelatin/chitosan films decreased Escherichia coli in liquid culture. Furthermore, Rocha et al. [113] established films made of anchovy protein that are antifungal and contain 1.50% (w/v) sorbic acid or benzoic acid.

3. Edible film manufacturing and coating application method

The edible film is commonly wrapped around a food product surface as a solid matrix and can act as primary packaging deprived of any sensory or nutritional appeal. Edible film can be utilised in the shape of pouches or sachets specifically for energy drinks and meal replacement shakes [8]. Aqueous solutions are transformed into edible films during the coating operation using specialised equipment. Only two basic converting methods – casting on steel belt conveyors and casting on a disposable substrate (such as release paper) on a coating line – are commonly employed to make edible films. However, a wide range of technologies are available for making thin coatings and films [114].

3.1 Casting

Casting (Figure 1) is a manufacturing process by which a liquid material is usually poured into a mould and then allowed to solidify [115]. The most popular method for forming films, known as solvent casting, is typically used at laboratory scales. Three fundamental steps are involved in casting a biopolymer-based movie: the biopolymer is dissolved in a suitable solvent, the solution is cast in a mould and the casted solution is dried [116]. To dissolve soy protein isolate polymer, the chosen polymer is dissolved or dispersed in an appropriate solvent (ethanol) [117]; this process is known as solubilisation. The resulting solution is poured into a glass plate with Teflon coating or a predetermined mould. The drying procedure gives the solvent enough time to evaporate, resulting in a polymer coating that adheres to the mould. For the casting of films to facilitate solvent removal and easy peeling of the film, air driers such as hot air ovens, tray dryers, microwaves and vacuum driers are used [118]. To improve the intramolecular interaction between the polymer chains and achieve a proper microstructure for the film, the air-drying process for casting edible film is crucial [119]. Quick-drying casting techniques have had a negative impact on the physical and structural qualities of the film [120]. The primary benefit of the casting method of film formation is its low cost and ease of production without the need for specialist equipment [121]. However, the film formation in solvent casting depends on the solubility of the polymer rather than melting [122].

In the casting process, following are the key drawbacks: (i) Limiting the forms (the simplest forms that frequently arise are simple sheets and tubes). (ii) Possibility of harmful solvent being trapped inside the polymer. (iii) Denaturation of proteins and other molecules that are incorporated into polymers using solvents [121]; vacuum drying of films can be used to remove the hazardous solvent [123]. (iv) A cap on the quantity of films that can be made [124]. (v) Films with various features can be created when evaporation levels and temperatures are variable [125]. (vi) Casting requires long drying time, which is not possible for commercial production [117].

3.2 Steel belt conveyors

Wherein the solutions are cast or spread uniformly on a continuous steel, then the moisture is removed by passing through a drying chamber. After being removed from the steel belt, the dry film is wound into mill rolls for subsequent processing. Additionally, the steel belt revolves around sizable drums that are located at either end of the line. With the aid of traditional coating equipment, the solution is evenly applied at one end of the line before being dried in a chamber. To avoid sticking or blocking, a thin, secondary dusting of starch powder may be applied to the dried film as it leaves the drying chamber. It is also decorated or marked with edible inks; given a variety of other treatments; and then taken from the steel belt and wound into enormous master rolls. In general, the steel belt conveyor lines (Figure 2) are 50–100 feet long when measured from the centre of the two drums. The widths of steel belts range from 20 to 60 inches. One of the highly desired characteristics of steel belt conveyors is the ability to directly cast aqueous solutions on the belt surface. This reduces the cost of a separate carrier web-like polyester film or coated paper while increasing uniformity, heat transfer and drying efficiency. However, some coating formulas could adhere to the steel belt too firmly. The coated substrate is then stripped from the belt and wound into a master roll [114].

Figure 2.
Steel belt conveyor. Source: Gamboni et al. [126].

3.3 Extrusion method

Extrusion is alternative technique used for producing polymeric films, and a pictorial view is given in Figure 3. This technique is preferred over a casting technique because it requires less energy and takes less time to remove water for making film [128]. It is one of the foremost polymer processing techniques currently in use at a commercial scale [129]. The extrusion process, commonly, is divided into three zones: (i) the feeding zone, (ii) the kneading zone and (iii) the heating zone at the final part/exit from the machine [130]. This technique best works with a minimum content of water or solvents; therefore, it is also called a dry process. However, to increase film flexibility, plasticisers are needed [131]. The mechanical (specific mechanical energy) and thermal energies (extruder barrel temperature) are involved in this method to yield an extruder-based edible film [132]. Certain parameters such as moisture content of the feed, screw speed, temperature of the barrel, the diameter of die, pressure at the die, energy input, etc. are critical for the extrusion process to influence the final products [127]. If high temperature is produced during the process, it affects the sensorial and nutritional properties of biopolymer of edible film which restrict its usage for high temperature with low moisture content FFS [133]. Co-extrusion is a method that can be used to create multi-layer films and gives flexibility in determining the required film properties. In addition to enhancing the produced film’s functionality and processing capabilities, the multilayer also benefits from the inventive structure of the multilayer film [134]. For preparing the edible film from pectin/starch blends added with pasticiser and glycerol, Fishman [128] used extrusion method in which extruder has nine heating zones and two screws. Liu [135] give optimal parameters/conditions for preparation of pectin film that must be 225 rpm and temperature should be 125°C in third zone and 110°C in fourth zone. These conditions were fixed on the basis of film’s physical and mechanical properties such as elongation, puncture strength, colour, thickness, etc. [136]. A short processing time with low energy consumption, better mechanical and optical qualities, such as elongation and transparency of edible film, are the key benefits of extrusion film formation over casting technique [129, 137]. It is a high-performance, inexpensive and efficient method utilised in the commercial food manufacturing industry [138, 139].

Figure 3.
Extrusion machine for polymeric films. Source: Suhag et al. [127].

3.4 Electrospinning

3.4.1 Principle

The process is chiefly carried out in three phases such as (1) jet initiation, (2) elongation and (3) solidification of solution (Masoud Aman [140]). An electrospining (Figure 4) having components such as syringe or capillary tube which transfer solution to which high voltage is given by using high-voltage battery followed by producing the nanofiber and solution is collected with the help of collector [142].

Figure 4.
Electrospinning machine for making biopolymer-based film. Source: Ebrahimi et al. [141].

A widely used technique for processing biopolymer-based film-forming solutions worldwide is electrospinning [143]. It is an economical method that can create thin films that could increase a material’s solubility and improve an application [144, 145]. In the electrohydrodynamic process used in electrospinning, a liquid droplet is electrified to create a jet, which is then stretched and lengthened to create fibres [146, 147]. For producing thin film, strong electric field is applied with small size orifice to spinneret (usually, a hypodermic needle with blunt tip). The diameter size of electrospun polymer fibre made by this technique generally is from 10 to 1000 nm and hence performs better electrical, mechanical and thermal properties than the synthetic packaging ([148] BG book). This electrospun fibre acts as an adhesion; hence, this can be used to combine two layers of biopolymer which increases the barrier properties of EF [149]. Electrospining technique helps to tightly hold two layers which maintain the thickness of film, and due to nanometric size of fibre, it enhances the mechanical property without affecting the optical property of the film [150]. The modified spinning process has plate die in place of spinneret which can produce flat film from casein [151]. Direct current (DC) or alternating current (AC) power supplies are both acceptable (AC). Surface tension causes the liquid to protrude from the spinneret and form a pendent droplet during electrospinning. When a droplet is electrified, the electrostatic attraction between surface charges with the same sign causes them to repel one another, transforming the droplet into a Taylor cone from which a charged jet is released. Due to bending instabilities, the jet first extends in a straight line before undergoing ferocious whipping motions. The jet is then compressed to smaller diameters, where it quickly hardens and deposits solid fibres on the grounded collector [152, 153]. Cui et al. [154] produced the nanofibers based on chitosan, gelatin and clove oil by electrospinning. The experiment of wrapping cheese by the obtained nanofiber for inhibiting microbial contamination proved that electrospinning was a creative strategy to fabricate nanofibers applied onto food [155]. Ebrahimi et al. [141] introduced a nozzle-less electrospinning device as a favourable technology to produce food-grade nanofibers on large scale with a high production yield in comparison to a nozzle-based instrument.

3.5 Thermoplastic method

The thermoplastic method uses shear pressures, high temperatures and little water to continuously shape the materials, allowing for industrial-scale large-scale manufacture of films [156]. It has been claimed that this technique can expand applications and get beyond the drawbacks of conventional techniques such as casting [157]. For chitosan films and gelatin films, the thermoplastic method – also known as the ‘dry process’ – involves extrusion strategy [158], blown approach [159], compression moulding [160] and the aforementioned combination [138]. The thermoplastic method, which is typically used for synthetic polymers, bio-plastics made from proteins, polysaccharides and other biopolymers, can be carried out as a continuous unit operation using control of temperature, size, shape and moisture [161]. For the most part, thermoplastic processing is an effective way to create chitosan or gelatin films for commercial uses in a wide variety of food products. However, there is no information available regarding thermoplastically manufactured chitosan-gelatin composite films [155].

4. Coating methods/technology

There are various methods used for the application of edible coting on the surface. For successful coating application food’s surface property plays an important role. It helps to give an overall equal thickness of coating material. Typical methods for forming a coating include panning, fluidised-bed processing, spray coating and dipping [114].

The coating is done in four steps:

Application of edible coating material or solution on the food surface using various coating methods.
Adhesion of edible coating material on the food surface.
The formation of a film on the surface of food is called “Coalescence’.
Stabilisation of coating layer on food surface by heating, cooling, drying.

4.1 Enrobing

In enrobing, the product to be coated is dipped in an edible coating solution or molten lipid (Figure 5). After a particular period, the fresh and frozen product produces a bland taste, moisture loss takes place and more oil absorption during frying, and to overcome this problem, coating with edible batter may improve palatability and flavour of it. This method is largely used in the chocolate industry. The principle behind using enrobing in the chocolate industry is to cover the centre of confectionery with tempered chocolate [114].

Figure 5.
Enrobing technique. Source: https://biztaskplus.com/chocolate-enrobing-how-it-works-using-a-chocolate-enrober/.

4.2 Pan coating

Pan coating or panning is used to apply thick or thick layers. Mainly this method is used for the hard and spherical products (Figure 6). It is conducted in the batch process, not in a continuous process [114]. It involved a perforated stainless steel pan in which coating solution is spread over the product with the help of a spray gun. The speed of the pan depends on the size of the product.

Figure 6.
Pan coating technique. Source: Agrawal and Pandey [162].

There are three types of panning methods used:

Hard panning – In this method, the hard coating of sugar syrup is applied by repeating the coating process. Applied sugar syrup coat is dried to form crystals on the surface.
Soft panning – In this method, a soft and thick layer is formed by applying the mixture of corn syrup and sugar to the product, and it is dried by applying dry sugar on it.
Chocolate panning – A fat-based coating is applied around the centre product. This coating could be of chocolate, white/coloured confectionery, etc. [163].

4.3 Drum coating

Drum coating is one of the methods through which a thin or thick layer can be applied to the hard or solid product (nut). Figure 7 illustrates the drum coating machine, it is run continuously. It is used in oiling and salting of nuts which enhance the palatability and flavour and helps to delay oxidation. In chocolate, this method of coating helps to delay the absorption of moisture.

Figure 7.
Drum coating machine. Source: Suhag et al. [127].

4.4 Screw coating and fluidised-bed coating

Screw coating is used to apply thin layer coating material on solid as well as firm food (Figure 8). It is a continuous process. To improve anti-caking of cheese, this coating method is used. For applying very thin layer of edible coating on dry particles having smaller size and very low density, this coating method is used mostly. Coating the powder by this method prevents agglomeration and enhances the dispersion and solubility of coating material [114].

Figure 8.
Screw coating. Source: Gamboni et al. [126].

4.5 Spray coating

Coating by spraying method helps to reduce in waste of coating solution by means of spraying system [80]. Spray coating is mainly preferred for that food which has large surface area [48]. The spray coating method is used mostly in combination with another method such as pan coating. But we can use it alone too. With the help of the spray coating method possible to spray molten chocolate, molten waxes, an aqueous solution or molten lipid in both thin as well as thick layers. For spraying, high-pressure nozzles are used but also the type of product which is coated. Spraying may be affected by fluid viscosity, temperature, pressure, the shape of the nozzle [114]. The apparatus for spray coating of wax on fruit and vegetables is patented by Cuning and Caulkins [164].

5. Functional properties of edible films and coating

5.1 Mechanical property

The edible bio-based film can resist normal external force created during handling and must have the proper mechanical property [155]. Mechanical property means film should be most effective in case of tearing resistance, stiffness, tensile strength, puncture resistance, bursting strength, etc. [61, 87]. Adequate mechanical strength ensures the integrity of a film and its freedom from minor defects, such as a pin hole, which ruin the barrier property. Coatings can also lessen damages to foods during handling and transportation. Sometimes, edible coatings and films may be used to change handling properties of materials. For example, edible films can encapsulate liquids or powders to improve handling. Simple protein films are stronger and more stretchable than composite films containing lipids. Lipid content was linearly associated to strength reduction. A WPC protein emulsion film with lipid of higher melting point exhibited better mechanical strength than that with lipid of a lower melting point [165]. Polysaccharide has lesser mechanical property than protein-based film. In the mechanical properties of the edible film, essential oil plays a vital role. Plasticiser helps to decrease tensile strength and increase the elongation property of edible film [112].

5.2 Colour property

Colour property is mostly used for selecting proper food packaging material [51]. Chitosan has its natural colour; due to this, chitosan edible film has higher greenness and yellowness and has lower lightness than commercial films [166]. Due to the presence of polyphenol in extract of chitosan-gelatin, the composite film became yellow [167]. The colour of the developed edible film can change the overall appearance of the food inside the packaging films. The edible film not only improves sensory quality but also affects the food quality due to that comes in contact with outer light. Therefore, the colour property requires proper and careful design to avoid this and for higher consumer acceptance [155].

5.3 Barrier property

One of the utmost important functions of edible packaging is barrier property. It cuts the contact of food with the external environment [168]. It includes oxygen barrier property, water barrier and light barrier property [169]. These properties are closely related to oxidation, microbial entrance and growth and spoilage in the food.

5.3.1 Gas barrier property

Oxygen and carbon dioxide affect the respiration of postharvest fruit and vegetables and also speed up the oxidation of lipid containing food [170]. Gas permeation and WVP have same mass transfer principle [171]. Oxygen barrier property is efficiently measured by parameter, i.e. oxygen permeability or rate of oxygen transmission through it. These are inversely proportional to each other [172]. By comparing chitosan and gelatin film, the chitosan-based film has good oxygen property than the gelatin-based film [173]. Although the gelatin-based film has a poor oxygen barrier, chitosan-gelatin-based composite edible film has excellent oxygen barrier properties. One of the main benefits of whey protein films over polysaccharide films is lower gas permeability. Gas barrier properties of milk protein films are also better than those of several commonly used in edible, synthetic films. This feature can be used to form integrated packages of milk protein films and synthetic polymer films [174]. Hydrocolloid films provide good oxygen barrier properties in the absence of moisture. Gelatin films can be used to cover candy and dry foods, microencapsulate flavours, and keep frozen meats from rotting. Moisture improves oxygen permeability by greatly improving the transferability of the macromolecule chains. Composite films composed of carboxymethyl cellulose and fatty acid sucroesters have adequate oxygen barrier properties while yet being somewhat CO₂ permeable [175]. On cooled bananas, this type of coating reduced CO₂ exchange by only around half while reducing oxygen transfer by five times. This result is influenced by the kind, variety and temperature of the fruit.

5.3.2 Water vapour permeability (WVP)/barrier property

For preserving food and increasing the shelf life of food, water vapour barrier property is considered mostly and importantly too [176]. The edible film should have low WVP because those films have low WVP and are mainly ideal for food that contains more moisture; it helps to avoid moisture transmission between food and environment which results in a better quality of food [171]. WVP can be reduced by adding an antimicrobial agent to it. Chitosan films show higher water vapour permeability properties than gelatin-based films [170]. The chitosan-gelatin composite film possesses hydrophilic nature, and it forms a compact network; due to this, it has higher water vapour barrier properties [170]. Whey protein films effectively bound the water vapour condensation in fruit and vegetable packaging, thus restricting microbial spoilage. For same reasons, the RH and plasticiser type considerably affect the moisture permeability properties of protein films [177]. Combining linear and globular proteins results in a decrease in WVP [178]. WVP was lowered by gelatin and defatted soy proteins from 8.45 to 5.55 g mm kPa-1 h⁻¹ m⁻² [178]. Plastisisers have an impact on WVP as well; it has been noted that utilising glycerol instead of PEG-400 and sorbitol results in greater WVP values. Sorbitol will provide the film with higher moisture barrier qualities because it is anticipated that edible films will have lower WVP [25].

5.3.3 Thermal property

The thermal property of edible film is related the resistance of that film to temperature which helps to protect food when stored in different temperatures. Thermo-mechanical property of film can be determined by scanning the calorimetry and thermo-gravimetric method [179, 180].

5.3.4 Antimicrobial property

The antimicrobial property of edible film is improved by adding the antimicrobial compound to it. The edible film also has carrier property so it carries antimicrobial agents, which play their role upon food when comes in contact with it. Antimicrobial activity of edible film containing antimicrobial agent is very effective against fungi and bacteria [171]. In chitosan-based edible film, mainly curcumin, apple peel polyphenols, etc are present [181, 182]. The Agar disc diffusion method is used to measure the antimicrobial activity of antimicrobial agent added edible film. Previously microorganisms inoculated film cuts are placed on agar plate and incubated in suitable conditions, and then the inhibition zone is observed around the disc films [183].

5.3.5 Moisture barrier properties

Films with appropriate moisture barrier properties are required for a great number of applications. Many lipid compounds, such as animal and vegetable fats, aceto-glycerides, surfactants and waxes [184], have been used in the formation of edible films and coatings because of their excellent moisture barrier properties. Waxy coatings on fresh fruit and vegetables thus reduce weight loss due to dehydration during storage by 40–75% [185]. A multicomponent film was established by Guilbert in 1986 [186] and is made of casein or gelatin, carnauba wax, glycerol monopalmitate and monostearate. This film demonstrated good water vapour barrier qualities when applied as an emulsion and subsequently acidified with lactic acid after drying. Krochta et al. [184, 187] also reported that the composite films of casein and aceto-glycerides or wax placed as an emulsion.

5.4 Edibility and biodegradability

The film is made from components that are totally edible, and if that is not eaten by consumers, also it has biodegradability property because it contains (environmentally safe) constituents or ingredients [15].

5.5 Carrier properties

Antioxidants, antimicrobial, flavouring compounds, pigments and nutrients are added to the film during the blending process of raw material. In such cases, a functional group of the film is bonded with these additives and makes the film stronger and has good carrier property [168].

6. Applications of edible film and coating in the dairy and food industry

6.1 Dairy industry

6.1.1 Paneer

Cinnamon essential oil–added edible film has excellent antioxidant as well as antimicrobial activity against spoilage and pathogenic microorganisms. Paneer packed in alginate-calcium edible film increases the quality of the panner during storage than the control sample of panner. It helps to increase its shelf life from 5–6 days to 13 days [188].

6.1.2 Cheese

The literature study suggests that cheese packaging is one of the potential application areas for edible packaging given that antimicrobial film in cheese has been found to have a significant impact on its shelf life. According to Fajardo et al. [189], saloio cheese’s storage stability was increased by employing chitosan-based film as a natamycin carrier; they also discovered that the product was stable for 7 days in ambient storage settings. Cheddar cheese was covered in whey protein films, and they discovered that the coatings preserved the products’ features and sensory attributes normally [190].

The goal of an edible whey-protein-based coating packed with antimicrobial agents is an efficient approach to stop the development of harmful germs and increase in shelf life of the product. Ricotta cheese coated with chitosan/whey protein edible film and stored at 4°C for 30 days exhibited a significant reduction in mesophilic and psychrotrophic counts compared with control [191]. Henriques et al. [192] stated that edible whey protein concentrate coatings prepared by heat denaturation or UV irradiation and merged with antimicrobials (lactic acid and natamycin) seem to be a potential alternative for commercial coatings in ripened cheese.

For prolonging the shelf life of low-fat cut cheese, it is coated by edible material added with oregano essential oil, which acts as antimicrobial as a mandarin fibre, which is based on nano-emulsion by retarding the growth of microorganisms during storage of low-fat cut cheese [193]. Zein-based blend coating helps to lower the weight loss by 30% and also helps to avoid microbial contamination of mode cheese or short ripening period cheese for more than 50 days as normal unpacked cheese sample gets contaminated after 21 days [194]. Shelf life of Mongolian cheese coated with water chestnut starch-chitosan film is determined at 8°C. This film contains perilla oil which acts as an antimicrobial agent and also helps to reduce weight loss [195]. The active coating of mozzarella cheese helps to retard the growth of microorganisms, and also it improves its sensory quality of it. It includes the addition of potassium sorbate (PS), sodium benzoate (SB), calcium lactate (CL) and calcium ascorbate (CA). Potassium sorbate gives the best effect than others. It increases its shelf life too [196].

6.1.3 Ice-cream holding edible cone

Ice-cream cone is mainly made up of flour and sugar, and it contains acetylated monoglycerides and has good moisture barrier property, which holds the ice-cream for longer as well as it is edible too. The chocolate coating of cone is used as a barrier which maintained the crispiness of that cone [197].

6.2 Food industry

6.2.1 Edible packaging of red chilli from mango kernel starch (MKS)

Red chilli is packed in mango kernel starch (MKS) as a sample and commercially PE packed red chilli as control. By comparing this for 6 months at 40°C, MKS packed chilli powder gives better results in pungency and colour. MKS film is produced by casting method which contains glycerol and sorbitol in a 1:1 ratio. This MKS film also helps to increase the shelf life of red chilli powder [198].

6.2.2 Edible coatings for fresh fruits and vegetables

The film is formed by adding fruit purees which interact with biopolymer and active compound of film material, which helps to increase shelf life of perishable foods [70]. Rangel-Marrón et al. [199] studied that papaya puree is added to the edible coating, increases the shelf life of minimally processed pumpkin, carrots, papaya, etc. For enhancing the shelf life of cut mango, composite coating is made from mango puree, gaur gum, sesame protein and calcium chloride. This composite coating aids to decrease the degradation of ascorbic acid, carotenoids and phenolic content lever of fruit [25]. In fresh-cut fruits and vegetables, protein-based edible coatings can act as moisture or gas barriers, which may reduce moisture loss and/or reduce oxygen intake from the environment and later reduce the respiration rate [200]. Edible whey protein coatings in apple and potato slices act as oxygen barriers and delay browning reactions [201]. Tien et al. [202] reported that whey protein isolate seems to possess superior antioxidant capacity than calcium caseinate. Whey protein concentrate and bees-wax-based coatings with 1% ascorbic acid or 0.5% cysteine are revealed to be the most effective means of preventing browning in apples [203]. Whey protein isolate coatings on freeze-dried strawberry pieces in milk revealed substantial reduction of rehydration ratio, resolving the problems of ‘rapid rehydration velocity’ and ‘loss of freeze-dried strawberry texture’ [204]. By reducing moisture loss and preventing microbial growth, edible coatings made with whey protein/pectin in the presence of TGase significantly delay the onset of spoilage in fresh-cut apples, carrots and potatoes for up to 10 days. However, their antioxidant properties, hardiness and chewiness were unaffected. According to Ochoa et al. [205], edible layers made of natural were derived from Euphorbia antisyphilitica with the potent antioxidant 0.01% elegiac acid which can significantly increase the quality and shelf life of exquisite golden apples (EA). Lower oxidative and hydrolytic rancidity and better sensory quality were found in walnuts and pine nuts covered with a homogenised coating solution of whey protein isolate and carnauba wax [86].

6.2.3 Egg and meat-based products

According to Caner [206], the whey protein film significantly extended the fresh egg quality’s shelf life when kept at room temperature. Eggs covered with whey protein lost weight while kept at room temperature for around 4 weeks, but control eggs gained weight by 5.66%. (uncoated eggs). Additionally, coated eggs showed better albumen quality and a lower pH than control eggs. Even after 4 weeks, the coated eggs’ yolk index values of 0.26–0.9 showed good quality.

Whey protein films significantly substantiated the decline in lipid oxidation and inhibition of the growth of spoilage and pathogenic microorganisms in meat products [207]. Shon and Chin [208] informed that the whey protein packaging mixed with natural antioxidant extracts revealed the reduction in the moisture loss and showed lower thiobarbituric acid-reactive substances and peroxide values (PV) in sausage and cooked meatballs when stored for 8 weeks at 4°C. Fernandez-Pan et al. examined the effects of a number of essential oils from oregano, clove, coriander, laurel, mastic thyme, rosemary, sage and tea tree on WPI films used for coating fresh skinless chicken breast (2012). The findings demonstrate that films containing essential oils reduced Listeria innocua, Pseudomonas fragi, Staphylococcus aureus and Staphylococcus enteritidis, with oregano oil demonstrating the strongest suppression. Similar to this, turkey meat’s shelf life was increased by Ferulago Angulate Essential Oil (FAEO) (0.05%) added to a gelatin-chitosan-based film (Naseri et al.).

Fresh meat has such biological composition that makes it perishable. Fresh meat contains 12–20% protein, 0–6% carbohydrates and 3–45% fat and muscle tissue has 42–80% water, approximately 75.5% [209]. As fresh meat has much amount of moisture in it, this condition is susceptible for microbial growth. To avoid such condition, packing of fresh meat in edible film has antimicrobial activity, which retards the growth of microorganisms as well as enhances the flavour of meat [171].

6.2.4 Edible coating for deep fat-frying products

Mashed potato balls were coated with corn zein, hydroxyl propyl methyl cellulose (HPMC) or methyl cellulose (MC) film-forming solution and uncoated considered as control. By comparing the control sample with a coated sample of potato balls, in coated ball observed that there is reduction in loss of moisture 14.9%, 21.9% and 31.1% in CZ, HPMC and MC coated ball, respectively. Also reduction in fat uptake by the ball is observed, 59.0%, 61.4% and 83.6% in CZ, HPMC and MC respectively. MC has the most effective barrier properties [210].

6.2.5 Seafoods

The majority of seafood, which includes fish and fish products, has a short shelf life due to the rapid proliferation of germs, which can endanger the health of consumers and cause a financial loss. Castro et al. [211] demonstrated the effectiveness of a film made of whey protein concentrate and green tea extract when applied on fresh salmon. They discovered that this combination successfully postponed the oxidation of the salmon’s lipids until 14 days after storage. Red sea bream’s shelf life was dramatically increased after ginger essential oil, fish sarcoplasmic protein and chitosan were combined with the fish. These three ingredients significantly decreased oxidation and protected against microbial decay [212]. The majority of the fat in salmon is easily digestible unsaturated fatty acids.

6.2.6 Nuts

When combined with high heat treatment during the roasting process, peanuts’ high oil and unsaturated fatty acid content makes them highly susceptible to oxidative rancidity. The main cause of oxidative rancidity in roasted peanuts is autoxidation. Depending on the oxygen levels in storage, lipid oxidation is the most frequent reason for peanuts to degrade [26]. In the presence or absence of vitamin, native and heat-denatured WPI coating postponed oxidation and increased the shelf life of peanut to 31 weeks at 40, 50 and 60°C [213]. According to Maté et al. [214], whey protein isolate (WPI) film or coating created with ascorbic acid (AA-WPI) considerably slowed down the oxidation of lipids in peanuts kept at 23, 35 and 50°C. All of the aforementioned temperatures saw the AA-WPI covered.

7. Advantages and disadvantages of edible film and coating over commercial synthetic packaging

7.1 Advantages

Edibility and biodegradability film and coating can be consumed directly with contained product, which does not produce any waste for decomposition, and if some consumer dose not eaten film with food, that film can be thrown and has no negative effect on the environment because of its biodegradability. It has the same biodegradability as it contains food.
The edible film has various additives such as flavouring, colouring and sweetening which enhance the organoleptic properties of packaged food.
Edible film and coating can be used for individual packaging of small size food such as peas, beans, nuts, etc. which is not possible in synthetic packaging.
Incorporated between food layers – edible film can be incorporated into two-layers of food which helps to reduce deterioration of inter-components of food such as pizza, pies, etc.
Edible film and coating have various functional properties such as antimicrobial, colour, mechanical, etc. which make it superior to synthetic packaging.
The edible film can be used for encapsulation of flavouring and leavening agent to control its addition to a particular product [215].
Has less gas, aroma and WV permeability [16].
Level of carbon dioxide inside the food decreases.
Helps to reduce emission of greenhouse gas level [30].

7.2 Disadvantages

More expensive than synthetic packaging – the edible film has various additives and manufacturing methods which make it more expensive than synthetic packaging.
Required secondary packaging – in some cases like an ice-cream cone, it holds the ice-cream but for packaging, it required secondary paper packaging over it.
Unable to use in unsanitary condition – edible film can be eaten directly with food but in unsanitary condition, consumers are unable to eat such film directly [16].
Biopolymers contain some particle of metals.
Has low mechanical and physical property.
Pollution in ocean cannot be fully resolved by it [30].

8. Comparison between edible films and synthetic film

Table 2 shows the comparison of WVP of edible film with synthetic packaging (PP, LDPE, etc.). Puncture strength of trilayered edible film from sodium alginate emulsion, gelatin emulsion and whey protein isolates emulsion (SAOGOWPIO) is seven times higher than that of synthetic packaging, and also edible film has more resistance to oxygen permeability than PS and PET [216]. Table 3 shows the mechanical properties of different types of synthetic as well as edible packagings, from that we can say that in case of some mechanical properties, edible film is deprived than synthetic packaging, but it was acceptable [216].

Properties
Packaging material	Elongation (%)	Tensile strength (MPa)	Young’s Modulus (MPa)	References
Synthetic packaging
PET	136.94	—	—	[216]
LDPE	500	9–17	—	[217]
HDPE	380	20.3	911	[218]
Edible film
Chitosan	4.60	74.0	2451	[219]
Whey potein isolates	10.08	5.34	—	[220]
Soya protein isolates	3.95	1.93	1.19	[221]
Quinoa starch	58.14	7.56	4.59	[222]

Table 2.

Comparison of mechanical properties of edible film with synthetic packaging.

Properties
Packaging material	WVP [10⁻¹¹ g.(m.s.Pa)⁻¹]	References
Synthetic film
Aluminium	0.0005	[223]
HDPE	0.002	[224]
LDPE	0.014	[225]
PP	0.010	[225]
PVC	0.041	[225]
Protein film
Wheat gluten	12.97	[226]
Corn zein	11.6	[227]
Soya	281.18	[228]
Lipid film
Waxes	0.03–1.0	[224]
Carauba wax	0.114	[225]
Paraffin	0.023	[224]
Polysaccharide film
Starch	25–78	[229]
Cellulose derivatives	9.2–11.0	[227]

Table 3.

Water vapour permeability of edible film vs synthetic film.

9. Conclusion

This review assembles the information about the need for the edible food packaging in dairy and food industry. Edible packaging can be used in two forms, i.e. film and coatings. Based on raw material, edible film and coatings are classified (polysaccharide, lipid and protein films and coating). Here, the importance of films and coating additives is also discussed, which helps to enhance the shelf life of contained food product by retarding the growth of microorganisms and bacteria, these additives also help to improve the mechanical properties such as a barrier, various strength. Different additives have their own function or effect on film and coating. The edible film has various methods of manufacturing such as casting, thermoplastic, extrusion, etc., and coating can be applied by using methods such as dipping, brushing, enrobing, panning, etc.; these methods are used to form a uniform layer on the food material and help to control the physical, mechanical and biological hazard effect on food. This review also confirms that dipping (coating method) and casting film-forming methods are the cheapest and easy methods to use at the laboratory level. Edible film and coating have various functional properties such as colour property, mechanical property, barrier property, edibility and biodegradability, etc.; this property makes the edible film and coating superior to the commercial packaging of food. Nowadays, edible film and coating have various uses/applications in the food as well dairy industry due to its positive effect on contained food. Different edible films such as starch-chitosan film contain natural antimicrobial used to improve shelf life of various cheeses. Coatings such as zein-based coating for mode cheese and nano-emulsion-based edible coating for low-fat cut cheese are used to enhance its shelf life. Edible film and coating are also used in the meat and meat product industry, deep-fat fried industry and bakery industry. From this review, it is concluded that the use of edible film and coating is suitable for dairy as well as various food industries and helps to reduce industrial waste and environmental pollution because of their edibility and biodegradability.

10. Self-citation

Self-citation is used for chapter writing.

Acknowledgments

We are grateful for the help and support provided by MAFSU, Nagpur, and Agriculture University Jodhpur, Rajasthan.

Conflict of interest

The authors declare no conflict of interest.

J. Pradhan

Chapters authored

Related collaborators

Jolanta Kumirska

Mirko X. Weinhold

Małgorzata Czerwicka

Zbigniew Kaczyński

Anna Bychowska

Hiroshi Tamura

Rangasamy Jayakumar

M. Prabaharan

Tetsuya Furuike

Shantikumar V. Nair