## 4 The Role of Edible Coatings in the Enhancement of the Postharvest Quality of Apples
Many hypotheses indicate that the reduction of damage to fruits sensitive to storage at temperatures below 10-12 \({}^{\circ}\)C is influenced by the strengthening of antioxidant systems or maintaining cell integrity, which allows for achieving lower phospholipase and lipoxygenase activity. Moreover, water-soluble alginate films can become insoluble material by cross-linking with divalent or polyvalent cations, e.g., Ca\({}^{2+}\). On the other hand, adding cross-linking agents such as calcium chloride (CaCl\({}_{2}\)) improves the mechanical properties of edible alginate films and reduces the penetration of water vapour and oxygen. CaCl\({}_{2}\) is also a commonly used solution to achieve fruit firmness in fruit processing. Research shows that a sodium alginate-based coating cross-linked with Ca\({}^{2+}\) is a promising alternative to chemical treatments, reducing the occurrence of brown spots and fruit shrinkage. The use of CaCl\({}_{2}\) by forming bonds with Ca\({}^{2+}\) may reduce the activity of enzymes responsible for softening and respiration, such as polygalacturonase [175]. The effectiveness of preserving bioactive ingredients, including vitamin C, and the total content of flavonoids and anthocyanins in stored apples was obtained by coating the fruit with the addition of aloe vera gel. Edible coatings in various concentrations (50, 75, and 100 \(v/\)%) were applied to waxed apples and then stored for 12 days at 10 \({}^{\circ}\)C. The limited oxidation of ascorbic acid could be due to the low permeability of the aloe-based gel coatings, and thus the enzyme activity was reduced. There was also a tendency to reduce the weight loss of apples and to delay the increasing titratable acidity, which suggests a  
Figure 4: The example of uncoated and coated apples with apple pectin-based edible coatings before and after 1 week of storage (The own study). delay in the deterioration of the quality of stored fruit. The moisture loss of apples could be due to the hygroscopic properties of the aloe vera gel, which probably formed a barrier between the fruit and the environment, thus preventing moisture from entering [176]. Apples (_Anocardium occidentale_ L) were subjected to four treatments: hydro-cooling at 5 \({}^{\circ}\)C, hydro-cooling at 5 \({}^{\circ}\)C combined with the application of calcium chloride, coated with solutions obtained based on corn starch, and coated based on corn starch with the addition of calcium, were stored in refrigerated conditions for 25 days at 5 \({}^{\circ}\)C. Hydrocooling is a postharvest treatment to reduce residues and microbes by spraying or dipping in cold water. It was observed that hydrocooling delayed weight loss, reduced peroxidase activity, and reduced the decomposition of vitamin C, dye, carotenoids, and anthocyanins. As a consequence, hydrocooling had a beneficial effect on limiting unfavourable visual changes. On the other hand, adding calcium affected the preservation of apple firmness and lower activity of pectin methylesterase and polyphenol oxidase. In the research conducted by [PERSON] et al. [177], it was proved that coating \"Granny Smith\" apples with coating solutions containing zein or zein in combination with nisin delayed their weight loss compared to uncoated apples. After 21 days of fruit storage at 15 \({}^{\circ}\)C, a 30% loss in the initial weight of uncoated apples was noted, a 25% loss in weight of apples coated with zein and nisin, and a 17% loss in weight occurred in the case of fruits covered with zein. The decrease in apple mass loss could be due to the ability of the coating to constitute a modified water vapour barrier by blocking the pores present in the skin. The highest retention of apple firmness during storage was found in the case of samples coated with zein, which could be caused by the limitation of the metabolic activity of enzymes affecting the decomposition of the cell wall--pectinesterase and polygalacturonase.