*3.5. Total Soluble Solid*

Figure 8 shows the results of the analysis of total soluble solids in minimally processed watermelon coated with an edible coating of a gelatin composite enriched with black tea extract. Total dissolved solids can be used to interpret the amount of sugar in the material and can be used as an indicator of the level of fruit maturity. The total dissolved solids values in all the treatments tended to increase significantly during the storage period (*p* < 0.05), and on the 13th day of storage, there was a slight decrease, as shown in Figure 8. However, the increase in the total dissolved solids values in the treated sample's edible coating was not as high as in the sample without treatment (control). This could be because the coating can inhibit the rate of metabolism of the polysaccharides, allowing the sugar content in the fruit to be maintained [18]. riod (*p* < 0.05), and on the 13th day of storage, there was a slight decrease, as shown in Figure 7. However, the increase in the total dissolved solids values in the treated sample's edible coating was not as high as in the sample without treatment (control). This could be because the coating can inhibit the rate of metabolism of the polysaccharides, allowing the sugar content in the fruit to be maintained [18].

Figure 8 shows the results of the analysis of total soluble solids in minimally processed watermelon coated with an edible coating of a gelatin composite enriched with black tea extract. Total dissolved solids can be used to interpret the amount of sugar in the material and can be used as an indicator of the level of fruit maturity. The total dissolved solids values in all the treatments tended to increase significantly during the storage pe-

no significant difference (*p* > 0.05) between treatments on the same day. a–e Values followed by the same non-capital letters showed no significant difference (*p* > 0.05) between storage times in the

There was a decrease in pH in all the treatments during the storage period. This was presumably due to the activity of the microorganisms that can convert sugar into organic acids. It can be seen in Figure 6 that the decrease in pH in samples treated with an edible coating enriched with the addition of black tea extract was not as sharp as in the control, because chitosan and black tea, as components of edible coatings, have antimicrobial activity, and the combination of gelatin and chitosan can increase the antimicrobial properties of chitosan [22]. Fruits are a naturally existing source of several organic acids such as Vitamin C. Vitamin C (ascorbic acid) degradation occurs during storage because it is highly sensitive and is lost upon exposure to heat, light, oxygen metals, and enzymes. Coating treatments have been shown to reduce the loss of organic acids such as ascorbic acid in fresh/fresh-cut fruits. Usually, ascorbic acid content decreases with the storage of fruits, irrespective of whether the fruit is covered with a coating or not, but the extent of

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the loss may be less in fruits that are coated [23].

same treatment.

*3.5. Total Soluble Solid* 

**Figure 8.** Effect of edible coating of gelatin composite enriched with black tea extract on total soluble solids (% Brix) of minimally processed watermelon during storage. The value shown is the average of the three experimental replications. A–C Values followed by the same capital letters showed no significant difference (*p* > 0.05) between treatments on the same day. a–c Values followed by the same non-capital letters showed no significant difference (*p* > 0.05) between storage times in the same treatment. **Figure 8.** Effect of edible coating of gelatin composite enriched with black tea extract on total soluble solids (% Brix) of minimally processed watermelon during storage. The value shown is the average of the three experimental replications. A–C Values followed by the same capital letters showed no significant difference (*p* > 0.05) between treatments on the same day. a–c Values followed by the same non-capital letters showed no significant difference (*p* > 0.05) between storage times in the same treatment.

During storage, the sugar content in fruit tends to increase due to the fruit ripening process; however, there is also a decrease in sugar content due to the use of sugar for fruit respiration and the activity of microorganisms. Chitosan has antimicrobial properties, and the combination of gelatin with chitosan can increase the antimicrobial properties of chitosan [27–29]. In addition, the addition of black tea extract can also increase the antimicrobial properties of the edible coating because tea has antimicrobial activity. Figure 7 shows that the addition of black tea extract to the edible coating solution affected the total soluble solids value in the minimally processed watermelon samples stored at a temperature of ±4 ◦C for 13 days, but there was no significant difference (*p* > 0.05) with the addition of 0.25–1% black tea extract. Often the studies involving the coating of fruit indicate that the TSS increases over time. One obvious reason for this increase is the progress in the ripening process leading to increased TSS. However, another justification for this increase is associated with the fact that water loss happens during the storage, which raises the TSS; this is a reason which has been cited in several studies [23].

#### *3.6. Antioxidant Activity*

Figure 9 shows the results of the analysis of the antioxidant activity in minimally processed watermelon coated with an edible coating of a gelatin composite enriched with black tea extract. Based on Figure 9, there was a significant decrease in antioxidant activity (*p* < 0.05) in all the treatments during the storage period. The storage duration of fruits and vegetables affects their antioxidant activity: the longer the storage period, the lower the antioxidant activity due to the respiration processes [12]. The preparation and storage process can affect antioxidant activity in minimally processed watermelon samples because

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this is a reason which has been cited in several studies [23].

*3.6. Antioxidant Activity* 

antioxidant compounds are sensitive and easily damaged when exposed to oxygen and light. In this study, the samples were stored for 13 days in transparent plastic cups that were translucent so that they could damage the antioxidant compounds contained in them. that were translucent so that they could damage the antioxidant compounds contained in them.

Figure 9 shows the results of the analysis of the antioxidant activity in minimally processed watermelon coated with an edible coating of a gelatin composite enriched with black tea extract. Based on Figure 8, there was a significant decrease in antioxidant activity (*p* < 0.05) in all the treatments during the storage period. The storage duration of fruits and vegetables affects their antioxidant activity: the longer the storage period, the lower the antioxidant activity due to the respiration processes [12]. The preparation and storage process can affect antioxidant activity in minimally processed watermelon samples because antioxidant compounds are sensitive and easily damaged when exposed to oxygen and light. In this study, the samples were stored for 13 days in transparent plastic cups

During storage, the sugar content in fruit tends to increase due to the fruit ripening process; however, there is also a decrease in sugar content due to the use of sugar for fruit respiration and the activity of microorganisms. Chitosan has antimicrobial properties, and the combination of gelatin with chitosan can increase the antimicrobial properties of chitosan [27–29]. In addition, the addition of black tea extract can also increase the antimicrobial properties of the edible coating because tea has antimicrobial activity. Figure 7 shows that the addition of black tea extract to the edible coating solution affected the total soluble solids value in the minimally processed watermelon samples stored at a temperature of ±4 °C for 13 days, but there was no significant difference (*p* > 0.05) with the addition of 0.25–1% black tea extract. Often the studies involving the coating of fruit indicate that the TSS increases over time. One obvious reason for this increase is the progress in the ripening process leading to increased TSS. However, another justification for this increase is associated with the fact that water loss happens during the storage, which raises the TSS;

**Figure 9.** Effect of edible coating of gelatin composite enriched with black tea extract on antioxidant activity (%) of sliced watermelon during storage. The value shown is the average of the three experimental replications. A–D Values followed by the same capital letters showed no significant difference (*p* > 0.05) between treatments on the same day. a–e Values followed by the same non-capital letters showed no significant difference (*p* > 0.05) between storage times in the same treatment. **Figure 9.** Effect of edible coating of gelatin composite enriched with black tea extract on antioxidant activity (%) of sliced watermelon during storage. The value shown is the average of the three experimental replications. A–D Values followed by the same capital letters showed no significant difference (*p* > 0.05) between treatments on the same day. a–e Values followed by the same non-capital letters showed no significant difference (*p* > 0.05) between storage times in the same treatment.

In the samples without treatment (the control), the decrease in antioxidant activity was higher than that of the samples treated with the edible coating because the diffusion In the samples without treatment (the control), the decrease in antioxidant activity was higher than that of the samples treated with the edible coating because the diffusion of O<sup>2</sup> into the tissue could not be inhibited. Antioxidant compounds are sensitive to oxygen, light, and high temperatures. Gelatin as a component of edible coatings has good barrier properties against oxygen and light; so, it can reduce the decrease in antioxidant activity during storage.

The addition of black tea extract to the edible coating solution can increase the antioxidant activity of the sample, as shown in Figure 9, because tea is rich in antioxidants. One of the hurdles in the food industry is the limited shelf life of foods due to the oxidation or degradation phenomenon. The addition of tea extract provides natural antioxidant compounds, and their addition to coatings could improve their functional characteristics, making them more effective in protecting fruits [23]. Many researchers have studied how edible coatings incorporated with antioxidants affect the quality and preservation of fresh/fresh-cut fruits. The addition of tea extracts is one of the several types of antioxidants used in coatings for fresh-cut fruits. The catechin, theaflavin, and thearubigin compounds in black tea have strong antioxidant abilities so that the higher the concentration of black tea extract added, the greater the antioxidant activity [14]. Antioxidant compounds can fight free radicals and increase tissue resistance so that they can reduce damage and decay due to fungal growth. Thus, the content of antioxidant compounds can affect the shelf life of the fruit. High antioxidant activity can increase the shelf life of fruit [5].

#### *3.7. Fungal Decay*

Our investigation showed that in all the treatments no samples were found that were damaged by fungal contamination during 13 days of storage at a temperature of ±4 ◦C. In this study, the selection of low temperature (±4 ◦C) and storage time for 13 days was motivated by previous experiments, which can be seen in Figure 10. Figure 10 shows that there was damage to the sample due to fungal growth on the 2nd day of storage at room

temperature (±25 ◦C) and on the 15th day of storage at low temperature (±4 ◦C). Storage at low temperatures (±4 ◦C) can inhibit fungal growth. Previous research showed that ciplukan fruit (Physalis peruviana), coated with an edible coating of gelatin and stored at ±5 ◦C, had a shelf life of up to 21 days and a lower percentage of damage due to fungal growth when compared to fruit storage at ±20 ◦C [30]. Storage at a temperature of ± 4 ◦C in minimally processed watermelon coated with an edible coating of sodium alginate can effectively reduce fungal growth until the 15th day [3]. temperature (±25 °C) and on the 15th day of storage at low temperature (±4 °C). Storage at low temperatures (±4 °C) can inhibit fungal growth. Previous research showed that ciplukan fruit (Physalis peruviana), coated with an edible coating of gelatin and stored at ±5 °C, had a shelf life of up to 21 days and a lower percentage of damage due to fungal growth when compared to fruit storage at ±20 °C [30]. Storage at a temperature of ± 4 °C in minimally processed watermelon coated with an edible coating of sodium alginate can effectively reduce fungal growth until the 15th day [3].

Our investigation showed that in all the treatments no samples were found that were damaged by fungal contamination during 13 days of storage at a temperature of ±4 °C. In this study, the selection of low temperature (±4 °C) and storage time for 13 days was motivated by previous experiments, which can be seen in Figure 10. Figure 10 shows that there was damage to the sample due to fungal growth on the 2nd day of storage at room

of the fruit. High antioxidant activity can increase the shelf life of fruit [5].

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activity during storage.

*3.7. Fungal Decay* 

of O2 into the tissue could not be inhibited. Antioxidant compounds are sensitive to oxygen, light, and high temperatures. Gelatin as a component of edible coatings has good barrier properties against oxygen and light; so, it can reduce the decrease in antioxidant

The addition of black tea extract to the edible coating solution can increase the antioxidant activity of the sample, as shown in Figure 9, because tea is rich in antioxidants. One of the hurdles in the food industry is the limited shelf life of foods due to the oxidation or degradation phenomenon. The addition of tea extract provides natural antioxidant compounds, and their addition to coatings could improve their functional characteristics, making them more effective in protecting fruits [23]. Many researchers have studied how edible coatings incorporated with antioxidants affect the quality and preservation of fresh/fresh-cut fruits. The addition of tea extracts is one of the several types of antioxidants used in coatings for fresh-cut fruits. The catechin, theaflavin, and thearubigin compounds in black tea have strong antioxidant abilities so that the higher the concentration of black tea extract added, the greater the antioxidant activity [14]. Antioxidant compounds can fight free radicals and increase tissue resistance so that they can reduce damage and decay due to fungal growth. Thus, the content of antioxidant compounds can affect the shelf life

**Figure 10.** Fungal decay on the 2nd day of storage at room temperature. (±25 °C) (**a**) and the 15th day of storage at low temperature (±4 °C) (**b**). **Figure 10.** Fungal decay on the 2nd day of storage at room temperature. (±25 ◦C) (**a**) and the 15th day of storage at low temperature (±4 ◦C) (**b**).

The antimicrobial nature of the edible coating may be due either to its inherent features or to an antimicrobial agent that has been added to the coating formulation, such as chitosan [29,31]. With reference to the literature, the antimicrobial potential of essential oils is the major reason for the incorporation of essential oils into edible coatings applied to fruits. The increased consumption of fresh-cut produce in recent times has raised the The antimicrobial nature of the edible coating may be due either to its inherent features or to an antimicrobial agent that has been added to the coating formulation, such as chitosan [29,31]. With reference to the literature, the antimicrobial potential of essential oils is the major reason for the incorporation of essential oils into edible coatings applied to fruits. The increased consumption of fresh-cut produce in recent times has raised the interest in antimicrobial coatings. The addition of plant extracts, such as tea extract, to edible coating formulations can improve the functionality of coatings in safeguarding fruits and vegetables from microbiological spoilage and hence extend their shelf life [23].

Fresh-cut fruits such as watermelon are convenient and ready-to-eat products that deliver advantages to consumers. However, the development of novel technologies to maintain the quality and extend the shelf life of fresh-cut fruits is a major challenge for the food industry and an issue of concern for future research. The use of edible coatings helps to maintain the quality of fresh-cut watermelon and extends its shelf life. In addition, coatings can be used to incorporate active/functional ingredients such as black tea into the fresh-cut produce. They can also perform effectively as carriers of bioactive compounds.

#### **4. Conclusions**

Treatment with an edible coating of tuna fish skin gelatin composite and chitosan enriched with the addition of black tea extract can inhibit weight loss and texture softening, as well as provide a protective effect against the discoloration of minimally processed watermelon which is stored for 13 days at ±4 ◦C. An edible coating treatment of tuna skin gelatin composite and chitosan enriched with the addition of black tea extract can inhibit acidity reduction and provide a protective effect against the changes in sugar content and the antioxidant activity of minimally processed watermelon which is stored for 13 days at a temperature of ±4 ◦C. Treatment with an edible coating of tuna fish skin gelatin composite and chitosan enriched with the addition of black tea extract can provide a protective effect against damage due to fungal contamination in minimally processed watermelon which is stored for 13 days at a temperature of ±4 ◦C.

**Author Contributions:** Investigation, S.S., A.S.S., H.B., A.A., F.A. and W.H.; Resources, E.S. and H.S.H.M.; Supervision, M., H.S.H.M., P.L.S. and A.N. All authors have read and agreed to the published version of the manuscript.

**Funding:** The authors would like Riset Kolaborasi Indonesia Program (RKI) for fiscal year of 2022 (NOMOR: 1575/UN1/DITLIT/Dit-Lit/PT.01.03/2022).

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Acknowledgments:** The authors would like to thank Riset Kolaborasi Indonesia Program (RKI) for fiscal year of 2022 (NOMOR: 1575/UN1/DITLIT/Dit-Lit/PT.01.03/2022).

**Conflicts of Interest:** The authors declare no conflict of interest.

### **References**

