# Sustainability in Bio-Based Edible Films, Coatings, and Packaging for Small Fruits
## 5 Edible Film and Coating Functionalities Important for the Small Fruit Industry
### Bioactivity of the Edible Films and Coatings
#### 5.1.1 Antimicrobial Properties  
The quantity and quality of microorganisms present in fruits after harvesting depends on the pH of the environment, water activity, and the availability of nutrients [111, 144, 145, 146]. Most small fruits, including berries, require storage at a reduced temperature. Hence, populations of bacteria from the genera Enterobacteriaceae (especially _Erwinia herbicola_ and _Rahnella aquatilis_) and Pseudomonasaceae (especially _P. fluorescens_) and some species of lactic acid bacteria (especially _Leuconostoc mesenteriodes_) may occur on the surface [147]. At the same time, the presence of various species of yeast from the genera _Torulaspora_, _Pichia_, _Tridosporon_, _Cryptococcus_, _Rhodotorula_, and _Candida_ is often observed, as their development is favored by the low pH of the fruit [148]. These pathogens on the fruit surface may lead to foodborne diseases. Several mechanisms are distinguished among the methods of preventing the development of pathogenic microorganisms (Figure 4) [148]. An alternative may be edible coatings, which, in addition to barrier properties, limit evaporation and water absorption or reduce ethylene production. These can significantly slow down fruit spoilage. They may additionally have properties that restrict the development of pathogenic microflora or contain additional substances with documented antimicrobial properties [149]. Polysaccharides, proteins, and lipid compounds can create edible coatings. Antimicrobial agents can be incorporated into the packaging material, coated on the surface of the packaging film, or added to the package in a s \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Fruit** & **Coating/Film Compounds** & **Activity** & **Reference** \\ \hline \multirow{8}{*}{Strawberries} & chia seed mucilage and bacterial cellulose nano-fiber & antioxidative & [136] \\ \cline{2-4}  & gum Arabic and bergamot pomace extract and oil & antioxidative & [137] \\ \cline{2-4}  & xanthan gum and sodium nitroprusside & antioxidative & [138] \\ \cline{2-4}  & chitosan and peny extracts & antimicrobial & [139] \\ \cline{2-4}  & chitosan & antioxidative & [128] \\ \cline{2-4}  & chitosan and leaf and olive pomace extracts & antifungal & [140] \\ \cline{2-4}  & gum Arabic carrageenanan and xanthan with lemongrass essential oil & anti-yeast & [141] \\ \cline{2-4}  & chitosan with gelatin, starch, and sorbitol with or without & & \\  & monoterpenes (geraniol and thymol) & antioxidative & [142] \\ \hline \multirow{2}{*}{Perishable fruits} & chitosanan derivatives conjugated with gallic acid & antioxidative and & [143] \\ \cline{2-4}  & antimicrobial & & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: _Cont._  
Figure 4: Mechanisms of antimicrobial action of edible coatings’ components (own work). Some of the polymers used to produce edible coatings have antimicrobial properties themselves. Such effects have been confirmed, among others, for polysaccharide films based on chitosan. Chitosan is obtained by the deacetylation of chitin, which improves its solubility in the starting material and facilitates the preparation of a film-forming solution. Additionally, its unique properties deserve special attention, i.e., confirmed safety of use, non-toxicity, biodegradability, biocompatibility, and potential applications in post-harvest preservation. Numerous studies of chitosan itself and films made from it confirm antimicrobial activity against many bacteria and mildew. Among the proposed mechanisms of this activity are the binding of positively charged chitosan glucosamine subunits to the negatively charged cell wall of the pathogen, which causes changes in the permeability of the cell membrane and the binding of chitosan to DNA, which results in the inhibition of cell division and, consequently, death [151; 152]. Similarly, the development of pathogenic microflora was inhibited by edible coatings made from other polysaccharides, such as guar gum [153] or gum Arabic [154], pectin [155], tucoidan [156], or even [157].