## 3 Edible Coatings
### Materials
The effective replacement of non-biodegradable materials with environmentally sustainable materials contributes to the promotion of a range of economically viable biomaterials. In addition, it is possible to convert them into value-added products, making waste treatment more efficient and reducing the generation of residues [98]. Edible coatings based on pullulan, a microbiologically obtained biopolymer, can form transparent films that dissolve in water. They can be applied directly to the surface of the food along with colour or flavour additives. They are recommended primarily for minimally processed fruits and vegetables due to their limiting effect on fungi [99]. Currently, the commercial pullulan market is estimated to be USD 130 million in 2023, where pullulan is mainly to be used for food packaging systems and pharmaceuticals. It arouses great interest in Japan, China, and the USA, mainly due to its good hydrophilic properties. Pullulan is often combined with other biopolymers, essential oils, sodium alginate, and whey protein isolate to provide improved physicochemical and physicochemical properties [100]. The proteins used to obtain film-forming solutions are materials of plant origin, e.g., wheat gluten, and zein and animal origin, e.g., whey protein, casein, albumin, or gelatin [64]. Protein coatings are characterised by greater fragility and susceptibility to damage compared to coatings obtained from other materials [101], as well as lower tensile strength compared to polysaccharide films [102]. Maize, soybean, and wheat gluten proteins are mainly used to coat fruit and vegetables because they exhibit gas and lipid barrier properties at low relative humidity [103]. Corn zein, extracted from corn gluten, due to the high content of non-polar amino acids (proline, leucine, alanine), can contribute to obtaining hydrophobic coating materials. On the other hand, using gelatine for edible films results in good resistance to gases and oils but poor mechanical properties and low thermal stability. To remedy this, the addition of appropriate starch materials is recommended. Packaging films made based on wheat gluten are characterised by other properties. Thanks to the ability to cross-link after heating, low production costs, and easy availability, they are one of the favourite sources of protein used for edible packaging. Unfortunately, edible films and coatings containing gluten are brittle, tend to absorb water after processing, and are highly sensitive to pH values. To improve their physicochemical properties, various proteins, polysaccharides, and organic acids are added [67]. Milk proteins can form plastic, transparent, and tasteless films; e.g., casein in edible films affects their stability at different pH values, temperature, and salt content. To improve the properties of caseinate edible films, polyphenic compounds such as tannic acid, which affect the achievement of better cross-linking of casein, are added. However, using collagen with the addition of other biopolymers (alginate, agar) and silver nanoparticles to film-forming solutions shows antimicrobial activity against _L. monocytogenes_ and _E. coli_. The presence of functional groups in the amino acid side chain of proteins causes covalent and non-covalent cross-linking, which leads to increased insolubility and elongation of the film. It is probable that the conformational changes of proteins after cross-linking cause an increase in the hydrophobic surface at a contact angle greater than 90 \({}^{\circ}\)C. An increase in surface hydrophobicity was also observed during the heat treatment of food proteins, resulting from changes in the secondary and tertiary structure by breaking hydrogen bonds [104]. Currently, proteins from many other sources are also used, obtained as by-products or for desirable properties and nutritional value. They include, e.g., peanut protein, lentil protein, sesame protein, pumpkin seed protein, egg protein, or rice protein [67]. [PERSON] et al.