Investigation of the potential of citron, sweet lemon and sweet orange peels as herbal tea

In this thesis, herbal teas were produced using the peels of sweet lemon, sweet orange, and citron through different drying methods, and their sensory, chemical, and bioactive properties were analyzed. The drying methods used were freeze-drying, hot air drying (50°C for 48 hours), and microwave drying (90 W for 1 hour). The freeze-dried sweet orange peel tea showed the highest phenolic content (843.4 mg GAE/L), while the microwave-dried sweet orange peel tea had the lowest phenolic content (279.2 mg GAE/L). In terms of antioxidant activity, the sweet lemon peel tea had the highest values in both undigested (0.895 mmol TE/L) and digested samples (0.222 mmol TE/L in the gastric phase). The digestion simulations demonstrated that, phenolic content and antioxidant activity significantly decreased in all samples, although some compounds were preserved in later digestion stages. Sensory analysis results indicated that, the microwave-dried teas were the most preferred in terms of taste and aroma, with the sweet orange peel tea scoring the highest (6.78) in overall preference. In the volatile compound analysis, linalool (117,744 µg/L) was the most abundant compound in sweet lemon peel tea, naphthalene (37,081 µg/L) in sweet orange peel tea, and 2-Furanmethanol 5-ethenyltetrahydro-.alpha.,.alpha.,5-trimethyl-, cis- (77,460 µg/L) in pomelo peel tea. In the individual phenolic compound analysis, hesperidin (11,278 µg/mL) was found to be the dominant compound in sweet lemon peel tea, while protocatechuic acid (16,585 µg/mL) and chlorogenic acid (1,700 µg/mL) were detected in pomelo peel tea. Additionally, pesticide analysis revealed 0.137 mg/kg of azoxystrobin in sweet orange peel tea. In conclusion, the microwave drying method was identified as the most suitable method in terms of consumer preference, while the freeze-drying technique provided the best results for bioactivity. Citrus peels represent a valuable resource for waste management, and this study is expected to contribute to sustainability and healthy product development.