*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 [91–93]. 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].
