**3. Results and Discussion**

## *3.1. Physicochemical Properties of By-Products*

#### 3.1.1. Proximate Composition

Table 3 shows the proximate composition of the by-products. The moisture content of the samples ranged from 5.23% to 11.41%; protein content ranged from 2.66% to 8.48%, fat from 1.03% to 4.37%, and the fiber and ash contents ranged from 7.41% to 52.90% and from 1.51% to 19.60%, respectively. Carbohydrate content ranged from 16.88% to 64.36%. All the present by-products had a different composition (*p* < 0.05). The highest moisture content was found for DAP and the highest values of ash and protein content were noted for DPPP. These values are higher than those found by Anwar and Sallam [18]. When it comes to fat, DOP had a high value compared to other by-products. DTP, DPPSP, and DPP presented high fiber contents compared to other by-products (greater than 49%). It was found that DAP was rich in carbohydrates; the proximate composition of DAP was confirmed by Skinner and Gigliotti [50]. Differences between the proximate composition of by-products obtained in this study and the results of other studies may be due to geographic location, season, variety, ripeness, or processing.


water-holding

 capacity; *P*: *p*-value probability; *F*: F-value Fisher. a–f letters indicate a statistical different of means in the same column. (*<sup>p</sup>* < 0.05).

### 3.1.2. Water-Holding Capacity

As shown in Table 3, DOP presented the greatest water-holding capacity (7.42 g/g d.w), followed by DAP and DTP. There was no difference between the WHC of DTP, DPP, DPPP, and DPPSP.

The water-holding capacity of DOP was found to be higher than that reported by Ocen and Xu [51]. The water-holding capacity of DAP was previously demonstrated by Bchir and Rabetafika [52]. Various factors can affect the water-holding capacity of the powder, such as pH, the presence of hydrophilic components such as fiber and free hydroxyl groups, and flour porosity [53–55]. The substances with high WHC can be used as a functional ingredient to promote beneficial health effects, reduce calories, and change the viscosity and texture of processed foods [56,57].

#### 3.1.3. Pectin

As shown in Table 3, DOP had the highest pectin content (21.92%); a lower value was noted for DTP from 3.91%. As reported by Wang and Chen [58] the citrus peel is rich in pectin. Similarly, Sundarraj and Ranganathan [59] showed that citrus peel and apple pomace are the main sources of pectin. The pectin content in DPPP is 9.856%, which is a higher value than that obtained by Anwar and Sallam [18]; this difference may be due to the ripening stage of the fruit and the extraction method. The addition of pectin to bakery products can change their texture, WHC, and consistency behavior. The addition of pectin can also extend the shelf life and be used to replace fat due to their high oil-holding capacity, thus reducing calories without losing taste [60].
