VALORIZATION OF CITRUS FRUIT PEELS AS A SOURCE OF BIOACTIVE COMPOUNDS: INDIVIDUAL AND COMBINED EVALUATION

Among citrus fruits, orange and lime stand out as two of the most important and widely cultivated fruits worldwide. These fruits have attracted considerable interest due to their high polyphenol content, especially flavonoids. The aim of this study was to evaluate the phenolic content and antioxidant activity of lime and orange peels, both individually and in combination. Hydroethanolic extracts were prepared from Tahiti lime (Citrus latifólia) and Pêra orange (Citrus sinensis) peels. For the individual extracts, 2 g of each sample were used separately, whereas the combined extract was prepared using the samples at a 1:1 (w/w) ratio, totaling 2 g. Each sample was extracted with 30 mL of an ethanol/ultrapure water solution (30:70, v/v). The samples were subjected to magnetic stirring for 30 min at room temperature (20 ± 5 °C) and centrifuged at 10.000 ×g for 15 min. The supernatant was then collected and stored at −20 °C before analysis. Antioxidant activity (AA) was determined using the ABTS method, whereas reducing capacity, used as an estimate of phenolic content, was determined using the Folin Ciocalteu method (FRC). Absorbance was measured using a UV-Vis spectrophotometer at 754 nm for AA and 760 nm for FRC. Orange peel showed an AA value of 492.78 µmol Trolox equivalents (TE)/100 g, whereas lime peel showed 644.45 µmol TE/100 g and the combination of both peels showed 569.26 µmol TE/100 g. Regarding reducing capacity, values of 848.17 mg gallic acid equivalents (GAE)/100 g were observed for orange peel, 1,768.17 mg GAE/100 g for lime peel, and 1,434.83 mg GAE/100 g for the combined peels. The evaluated citrus peels showed relevant antioxidant activity and reducing capacity, with lime peel exhibiting the highest values for both parameters. The combination of the peels showed values higher than those observed for orange peel but lower than those obtained for lime peel, indicating an intermediate content of antioxidants. Orange and lime belong to the genus Citrus and have similar phenolic profiles, although they may differ in the concentrations of these constituents. This similarity in chemical composition may have limited possible synergistic interactions among their bioactive compounds. It should be noted that combinations of antioxidant phenolic compounds may result in different types of interactions, including synergistic, additive, or antagonistic effects. It is concluded that the combination of peels showed higher values than orange peel alone but lower values than lime peel. Overall, the citrus peels demonstrated potential as sources of bioactive compounds, highlighting the possibility of valorizing these residues. However, these results cannot be attributed solely to phenolic compounds, since Citrus fruits are also sources of vitamin C, has also an important antioxidant activity.

Acknowledgments: CNPq, FAPESC.