Effects of ultrasound-assisted extraction on physicochemical properties, bioactive compounds, and antioxidant capacity for the valorization of hybrid mandarin peels

Abstract

Samples of tree hybrid mandarins (´Clemenvilla`, ´Ortanique` and ´Nadorcott`) were employed to determine the physicochemical properties (increase of conductivity, brix° and pH), bioactive compounds (total phenolic, flavonoid, ascorbic acid and carotenoids content) and antioxidant capacity (DPPH and TEAC) of peels. Mandarin peel extracts were prepared employing ultrasound assisted extraction (400 W, 80% v/v duty cycle, 40ºC). The results were compared to the values of control extraction method. Aqueous ethanol solution (50%, v/v) was used as solvent in solid-liquid ratio of 1:10 (w/v). A 5, 15 and 30 min were applied in both methods to stablish the most effective extraction time. The increase of conductivity enhances with the extraction during 30 min. No significant differences were observed in ºBrix values; in case of pH, these differences were observed according to the varieties analyzed. The total phenolics, flavonoids, carotenoids and ascorbic acid content enhance as the extraction time increased until 30 min with significant differences according to the mandarin variety. ´Clemenvilla` peels treated by 30 min had the highest amounts of total flavonoids (76.7 mg CE/100g) and ascorbic acid content (136 mg AA/100g). ´Ortanique` and ´Nadorcott` peels had the highest values of total phenolic content (1230 GAE/100g) and total carotenoids (8173 μg β-carotene/100g), respectively. Antioxidant capacity values were stronger influenced by flavonoids and ascorbic acid content in both assays applied (DPPH and TEAC). Results indicated that ´Clemenvilla` and ´Ortanique` peel extracts by USN were the samples with highest values by DPPH and TEAC assays respectively (average of 12.2 and 25.7 mmol TE/100g, respectively).