**3. Results and Discussion**

## *3.1. Transpiration*/*Weight Loss*

The transpiration rates (expressed as percentage moisture loss) measured for fruit samples stored at 4 ◦C are shown in Figure 2a. Weight loss was measured every three days during storage in triplicate using 200 g of the control samples and 200 g of the coated samples stored in multiple plastic containers. During the 15 days of the experiment, overall, the moisture loss percentages in the coated samples were significantly lower (*p* < 0.05) than in the control samples. The weight loss in the control samples after three days of storage was 5.2%, slightly higher than 4.0% in the coated samples. Transpiration rates increased in both the control and coated samples during the experiment. On the final day 15, moisture loss in the control samples reached 13% while in the coated samples, it was 11%. Differences between the coated and uncoated samples were clear from day 3 onward. Moisture loss was reduced due to the water vapor barrier formed by the sodium alginate-calcium chloride edible coating on the fruit's surface (Figure 2a).

**Figure 2.** Moisture loss (%) (**a**), respiration rate (**b**), and firmness of control and sodium alginate-calcium chloride coated samples during storage (**c**). Different lowercase letters indicate a significant difference due to storage time (*p* < 0.05). Different uppercase letters indicate a significant difference among the control and coated samples (*p* < 0.05).

One-way ANOVA statistical analysis showed that there was a significant difference in moisture loss among the control samples and among the coated samples during storage (*p* < 0.05). A clear significant difference in moisture loss between the control and coated samples was observed starting from day 6 up to day 15 (*p* < 0.05). Moisture loss was significant with respect to time for both the coated and uncoated cut fruits. Moisture loss is also related to quality loss and the reduction in weight and volume (shrinkage or shriveling) of the fresh produce. It was also reported that the reduction of moisture loss in coated fruits during storage played an important role in the shelf life extension of the strawberry cut fruits. Formation of a layer of the alginate film obviously helped to reduce the moisture loss from the fruit by acting as a barrier [10].

#### *3.2. Respiration Rate*

The respiration rates of the control and coated samples were measured over the period of storage. The amounts of CO2 produced were measured every minute for 2 h using 150 g of both the control and coated strawberry cut fruits. The results were taken during the first hour until the saturation of CO2 [24]. Based on this methodology, the respiration rates measured (mL CO2 kg−<sup>1</sup> h<sup>−</sup>1) in the control samples were higher than the respiration rates in coated fruit samples over the whole period of the experiment starting from day zero. The sodium alginate-calcium chloride edible coating played an effective role in decreasing the respiration rates in the coated samples by reducing the amounts of CO2 produced. On day zero, the respiration rate in the control samples was 104 mL CO2 kg−<sup>1</sup> h−1, while it was 71.6 mL CO2 kg−<sup>1</sup> h−<sup>1</sup> in the coated samples. Previous studies showed that on day zero, the respiration rates in both the control and coated samples should be high due to the mechanical damage. The respiration rates decreased in the control samples on day 3 to 81.3 mL CO2 kg−<sup>1</sup> h−1, while in the coated samples, it decreased to 64.7 mL CO2 kg−<sup>1</sup> h−1. On day 6, the respiration rates in the control samples increased to 123.7 mL CO2 kg−<sup>1</sup> h−<sup>1</sup> and stayed stable until day 9, before it decreased to 68.5 mL CO2 kg−<sup>1</sup> h−<sup>1</sup> on day 15. In the coated samples, the respiration rate increased to 99.6 CO2 kg−<sup>1</sup> h−<sup>1</sup> on day 9, before it decreased to 55.5 mL CO2 kg−<sup>1</sup> h−<sup>1</sup> on day 15 (Figure 2b). The sodium alginate-calcium chloride coating reduced the respiration rates in strawberry cut fruits.

One-way ANOVA statistical analysis showed no significant overall difference between the control and coated samples (*p* > 0.05) (because of the consideration of the variation over the entire range rather than a direct one to one comparison). However, the differences were significant in the beginning and between six and 12 days of storage. Other studies have shown that calcium dips can be effective in reducing respiration rates in addition to extending the shelf life of cut fruits. A decrease in the respiration rates in cut cantaloupe dipped in a calcium salt solution and stored 4 ◦C was reported. This reduction is facilitated by the reduced oxygen and carbon dioxide permeability by the coating. This will not only result in reducing the oxygen tension within the fruit because of the lower infusion of oxygen into the tissue, but at the same time, reduced removal of the CO2 produced will thereby promote a higher concentration of CO2 within the tissue and the consequence of both will be a reduced respiration rate [26].

#### *3.3. Texture*

The firmness of the strawberry cut fruits was measured using seven to 10 samples of the control and coated samples, the results of which are shown in Figure 2c. Firmness of coated strawberry cut fruits decreased during the 15 days of storage at 4 ◦C. However, the coated samples showed better results than the control samples. A beneficial effect in the firmness retention was observed in coated samples during the 15 days of the experiment. Since day zero, the texture of the coated samples showed higher values than the control samples due to the added calcium chloride, which acts as firming agents as well as the lowered respiration and transpiration rates. The firmness of the control samples decreased from 57.3 N on day zero to 41.2 N on day 3, while in the coated samples, the firmness was almost stable during the first six days of storage. On day 6, the firmness in the control samples showed a dramatic decrease and declined to 11.8 N at the end of the experiment on day 15. In the coated samples, firmness declined only to 36.6 N on day 15, thus remained firm. Additionally, after 12 days of storage, it was difficult to perform the texture analysis on the control samples due to their extremely soft texture, while coated samples were still in good condition. The results showed the positive effect of the sodium alginate-calcium chloride edible coating on the texture of strawberry cut fruits, since a good texture was maintained over the whole period of the experiment. Values observed in coated fruits were three times higher than in the control samples (Figure 2c).

One-way ANOVA statistical analysis showed a significant difference in the firmness among the control samples after day 0 (i.e., from day 3 to 15) (*p* < 0.05). However, with the coated samples, no significant decline in texture was observed until day 9. Furthermore, a significant difference in the firmness between the control and sodium alginate-calcium chloride coated samples was observed starting from day 3 up to day 15 (*p* < 0.05).

Fruit softening during maturation is caused by the biochemical changes in the cell turgidity and the cell wall compositions. The changes are shown by a degradation of the middle lamella of the cortical parenchyma cells, and a decrease in the pectin content [24]. The addition of calcium chloride salts was reported to play an effective role in maintaining the firmness of the coated samples during storage, acting as firming agents [9].

## *3.4. Total Soluble Solids*

Total soluble solids (◦Brix) is used as an indicator of fruit maturity and is measured in fruits to study their maturation rates. Based on different studies, the total soluble solids content (TSS) in fruits increased during storage. The edible coating could reduce the TSS content by delaying the fruits ripening [27]. During the 15 days of storage, the TSS in the control samples was higher than in the coated samples, which suggests that sugars are synthesized at a slower rate due to the sodium alginate-calcium chloride coating. On day zero, the values of TSS were 7.7 in the control samples and 7.6 in the coated samples. TSS in the control samples increased to 8.3 on day 6, while in the coated samples, the TSS remained almost stable from day 0 until day 6 with a value of 7.6. The edible coating reduced the rates of carbohydrate breakdown and delayed fruit maturation (Figure 3a). The decrease in the TSS content at the end of the experiment is an important indicator of fruit maturation since it can indicate fruits over ripening [28]. One-way ANOVA statistical analysis showed an overall significant difference between the control and sodium alginate-calcium chloride coated samples during the experiment (*p* < 0.05). However, no significant difference was observed among the control samples or among the coated samples during storage (*p* > 0.05). The increase in TSS is related, first, to moisture loss and the increase in the soluble solid concentration. Moreover, it is related to the breakdown of complex carbohydrates into soluble solids due to the respiration and ripening of fruits. Starch is degraded rapidly into sugars such as sucrose, glucose, and fructose due to the activity of amylases, starch phosphorylase and 1,6-glucosidase enzymes [27].

#### *3.5. pH*

A significant increase in the pH of the control samples over the period of storage was observed. The pH of the control sample was higher than in the coated sample during the 15 days of the experiment. On day zero, the pH of the control and coated samples was 3.6. The pH of the control samples gradually increased and reached 3.8 on day 12, while in the coated sample, the pH was almost stable from day zero until day 12. The sodium alginate-calcium chloride edible coating reduced the pH of the coated samples in comparison with the control samples. Additionally, it delayed the increase in the pH values during storage (Figure 3b). One-way ANOVA statistical analysis showed a significant difference between the control and sodium alginate-calcium chloride coated samples during the 15 days of storage, especially day 3 onward (*p* < 0.05). The pH of the coated fruits remained higher than in the control samples throughout the study. A delay in the increase of the pH of strawberries coated with carboxyl methyl cellulose (CMC) was reported [22]. It has also been reported that the sodium

alginate-based edible coating delayed the increase in the pH of the fruit samples, which delayed fruit ripening and mold growth by maintaining the acidity of the fruits [27].

**Figure 3.** Changes in total soluble solids (TSS) (**a**), pH change (**b**), and titratable acidity of the control and coated samples during storage (**c**). Different lowercase letters indicate a significant difference due to storage time (*p* < 0.05). Different uppercase letters indicate a significant difference among the control and coated samples (*p* < 0.05).

#### *3.6. Titratable Acidity*

Titratable acidity (TA) was measured and expressed in citric acid (%). Based on the test results, the coated fruits had a higher citric acid (%) than the uncoated samples. On day zero, the titratable acidity was the same in both the control and coated samples. The acidity decreased at a slightly lower rate in the coated samples during the 15 days of storage. On day 6, a significant decrease in TA was observed

in the control samples and the value reached 0.088%, while in the coated samples, it decreased to 0.091%. On day 9, the TA decreased in the coated samples to 0.081% and stayed steady up to day 15. Additionally, in the control samples, TA declined on day 9 to 0.076% and stayed steady thereafter until day 15 with a value of 0.078% (Figure 3c). Coated fruits had a higher TA (%) during the 15 days of the experiment. The sodium alginate-calcium chloride edible coating minimized the reduction of fruit acidity compared to the control. However, one-way ANOVA statistical analysis did not show a significant difference in TA (%) between the control and coated samples (*p* > 0.05).

Titratable acidity is related to the organic acid content in strawberries. Acidity decreases at the late stages of fruit ripening due to the use of organic acids during respiration. Coating of strawberries with CMC and hydroxypropyl methylcellulose (HPMC) showed a delay in the decrease in TA (%) in strawberries. The edible coating reduced the loss of ascorbic acid during the 16 days of storage by reducing oxygen diffusion and respiration rates, which caused ascorbic acid retention [22]. Slower rates of decreased acidity were also observed in pectin coated cherry tomatoes stored at different temperatures [27]. Moreover, methyl cellulose coated peaches showed a delayed reduction in the titratable acidity [7,8].
