Vitamin C, Sugar Content, Color Intensity and Some Physicochemical Properties of Watermelon and Orange Peels

Objective: Peels generated as waste during the consumption and processing of fruits and vegetables contribute to both nutritional losses and environmental pollution. Due to their high nutritional content, raw material potential, and the aim of reducing environmental pollution, the use of certain fruit and vegetable peels in various forms and applications in the food industry is becoming increasingly widespread. This study investigates the usability of watermelon and orange peels in terms of their functionality by analyzing their vitamin C and sugar contents, color intensities, and some physicochemical properties. Methods: Glucose, fructose, and sucrose contents were determined by HPLC, vitamin C content by titrimetric method, protein content by the Kjeldahl method, color intensities by a colorimeter, and other properties using standard methods. Results: In watermelon peel, the dry matter content was found to be 3.57±0.27%, total acidity 0.59±0.01%, pH 5.74±0.02, total ash 0.65±0.02%, protein 1.76±0.01%, glucose 0.54±0.02%, fructose 1.26±0.06%, L* value 72.45±1.10, a* value -14.81±1.30, and b* value 35.91±3.46. Vitamin C and sucrose were not detected in watermelon peel. In orange peel, the dry matter content was 23.31±0.08%, total acidity 1.22±0.02%, pH 5.09±0.02, total ash 1.12±0.05%, vitamin C 122.33±2.52 mg/100g, protein 2.41±0.08%, glucose 2.18±0.12%, fructose 1.89±0.03%, and sucrose 0.28%. The color values were L* 68.92±0.47, a* 19.23±4.09, and b* 63.85±1.8. Conclusion: Based on the findings of this study, orange peel, which is produced in large quantities as waste in the industry, contains more nutrients, exhibits better color intensity, and has a significantly higher vitamin C content compared to watermelon peel. Therefore, orange peel can be used as a natural antioxidant and color source in the food, pharmaceutical, and cosmetic industries.