# Sustainability in Bio-Based Edible Films, Coatings, and Packaging for Small Fruits
## 3 Biological Sources of the Compounds Used in Films, Coatings, and Packaging
### Animal Processing Byproducts
#### 3.3.2 Materials from the Dairy Industry  
Many researchers are concerned with the biotechnological valorization of whey to produce value-added products. The leading group of dairy proteins found in cow's and goat's milk is casein, which is about 75-78% [83]; the remaining percentage includes whey proteins, among other components. Casein has four main subunits in its constitution: \(\alpha\)s1-casein (38%), \(\alpha\)s2-casein (10%), \(\beta\)-casein (36%), and k-casein (13%) that influence the degree of availability for the formation of films given its flexible structure. The polar and hydrophobic domains they present provide this high degree of flexibility. In addition to this property, other properties, such as high thermal stability and biodegradability, can also be recognized [78]. Edible casein coatings for fruits have high nutritional value and prevent excellent gas permeability barrier [84]. According to [PERSON] et al. [85], milk protein can be used to obtain several films. The interaction between the proteins will always determine the structure of the films formed. Mixing casein with other substances can produce great edible films and coatings [86]. Examples are the films obtained from casein and natamycin that control microbial activity and fungal growth [87], and the mixture of casein with beeswax obtained from emulsions to reduce white blush and increase resistance to water vapor [88]. Extended studies by [PERSON] and his collaborators [89], using a mixture of casein with different natural film waxes (bees-wax, candellilla, and carnauba wax) where potassium sorbate was integrated, showed bacteriostatic properties, controlling the growth of _E. coli_ up to 20 days of storage at 15 \({}^{\circ}\)C. [PERSON] et al. [90] concluded that caseinate films where sorbitol was added were less flexible than those with glycerol in their composition. The addition of plant extracts to casein-based films has also been studied. Therefore, supplementing the films with essential oils such as linseed oil [91], rosemary [92], cinnamon [93], and canola [94] demonstrated better moisture resistance, sound water barrier, and better strength and flexibility. Other additives incorporated into casein films or whey proteins have also been studied to improve their attributes, namely inorganic substances such as TiO\({}_{2}\) nanoparticles or ZnO [88], which stood out for presenting high antimicrobial activity. Halloysite, aluminum and magnesium silicate [95], sodium sulfite, sodium dodecyl sulfate, and urea [96], antimicrobial agents and preservatives such as E1105 (chicken egg lysozyme), viable strains of lactic acid bacteria and probiotic strains of various _Lactobacillus_ spp. and _Bifidobacterium_ spp. [97] can be added to those films. Whe proteins can be obtained using the main by-products of the dairy industry, such as cheese whey. They are globular proteins and form new polymeric structures through cross-linking, making them an excellent raw material for film production [98]. According to [PERSON] et al. [99], whey proteins, protein hydrolyses, and bioactive peptides, polymers of animal origin, are known to have natural antimicrobial properties. Although its mechanism of action is not yet fully understood, it is inevitable that factors such as temperature, pH, and fat influence its microbial activity. When whey protein nanofibrils were incorporated into edible films, inhibitory action was observed against bacteria such as _Listeria monocytogenes_, _Staphylococcus aureus_, _Escherichia coli_, and _Salmonella_ Enteritidis [100].  
Because they have bioactive peptides with antimicrobial activity and beneficial effects on consumers' health, whey proteins are a promising raw material for manufacturing coatings and films. In addition to their nutritional value [101], they help mitigate environmental impacts, contributing to sustainable industrialization [102].