# Effect of Chitosan Nanoemulsion on Enhancing the
## 4 Discussion  
Acidity is an important parameter in maintaining fruit quality, which is directly related to the concentration of dominant organic acids in samples [40]. Organic acids are used by the respiration reactions to provide the necessary energy for the normal activities of the cells in storage time [41]. Therefore, the acid content and the pH of the fruit reflect the status of the fruit from the senescence point of view. According to the results of this study, the total acidity content showed a decreasing trend and the pH showed an increasing trend over time, which can be due to the consumption of the organic acid in the respiration process and their conversion to sugars [31]. ECNPC, as any other coating, reduces the respiration and ethylene production rates by restricting the gas exchange resulting in elevated CO\({}_{2}\) and decreased O\({}_{2}\), thereby reducing the consumption of organic acids and preventing an increase in fruit pH [42]. Change in soluble solids depends on metabolic activities and the activity of different cell wall degrading enzymes. An increase in metabolic activities leads to enhanced ethylene production and a subsequent increase in the activity of degrading enzymes resulting in a dramatic increase in the TSS content of the fruit [43]. Therefore, any decrease in metabolic activities will decrease the ethylene biosynthesis and action resulting in the prevention  
Figure 5: Effect of chitosan nano-emulsion coatings (at 0 g L\({}^{-1}\), 2.5 g L\({}^{-1}\), and 5 g L\({}^{-1}\)) on antioxidant activity: (**a**) phenylalanine ammonia-ylase (PAL) enzyme activity and (**b**) guaiacol peroxidase (G-POD) enzyme activity of raspberries stored for 9 d (at 4 \(\pm\) 1 \({}^{\circ}\)C with 90–95% RH). Control refers to untreated raspberries. The data shown are the mean \(\pm\) standard error of four replicates. Different letters indicate statistical significance (\(p<0.01\)). of a dramatic increase in TSS content. By restricting the gas exchange and making a modified atmosphere in the fruit, chitosan coating decreases ethylene production and senescence rate and prevents cell wall degradation processes [44]. The positive effect of the ECNPC in retaining fruit firmness in this study demonstrates the effectiveness of this treatment in decreasing the activity of cell wall degrading enzymes probably by decreasing ethylene production and action. However, the effect of chitosan on soluble solids content is different for different types of fruit; for example, in papaya fruit, the coating did not have a significant effect on soluble solids but increased the soluble solids in mangos [45]. Weight loss of harvested crops is the consequence of water loss and the respiration process. With progress in senescence, the water of the fruit is lost due to transpiration; the weight loss is also related to the consumption of fruit carbohydrates and organic acid reserves. Water loss, in turn, accelerates senescence by enhancing the production of free radicals and ROS [46]. The amount of respiration and the consumption of sugar by the cell lead to more water loss, which is an important factor in the deterioration of the products [13]. Findings demonstrate that these films/coatings act as a barrier on the surface of fruit and vegetables, which causes higher moisture and water retention, creating favorable micro-environments by optimizing the concentration of gases and delaying the ripening process [47]. The role of chitosan-based edible coating is to restrict water vapor exchange between the fruit and the environment, decrease the respiration and metabolic activities, and activate the mechanisms of cuticle formation in the tissues. In fact, as an elicitor, chitosan can activate the PAL and polyphenol oxidase (PPO) enzymes and other enzymes playing roles in the biosynthesis of polyphenols and cuticle [48]. It is well demonstrated by researchers that these additives play an important role in extending the shelf life and maintaining the nutrient profile of numerous fruit and vegetables.