Antioxidant Activity, Composition and Application of Paulownia (Paulownia tomentosa) Fruits, Flowers and Shells

Paulownia is one of the most useful and sought-after trees worldwide. Various parts (flowers, fruits, leaves, wood, bark, and seeds) have found practical applications. The present study focuses on the characterization of paulownia fruits, flowers and shells, and their potential non-traditional application for pollutant adsorption. The fruits were found to contain higher amounts of flavonoids (1051.85 ± 10.32 µg mL−1) compared to flowers (401.26 ± 5.48 µg mL−1). This reflects the observed antioxidant activity of the fruits: two times higher than that of the flowers. Salicylic acid was the main phenolic acid (2729.96 ± 16.89 µg mL−1) in the flowers, while quercetin (572.42 ± 10.32 µg mL−1) and rosmarinic acid (352.84 ± 6.97 µg mL−1) were present in higher amounts in the fruits. The lipids from the flowers were rich in linoleic (48.1%) and linolenic (20.0%) acids, while the fruit lipids were rich in linoleic (53.9%) and oleic (19.5%) acids. More than half of the fruits and flowers consisted of insoluble dietary fibers. The shells were rich in cellulose and lignin (42.96 ± 0.61 and 31.23 ± 0.34 g 100 g−1 DW, respectively) and were applied as a natural biosorbent for Cu2+, Cd2+ and methyl orange removal (99.05%). Paulownia fruits were effective, removing 98.25% of Cu2+ (5000 mg L−1). Hence, paulownia shells and flowers could potentially be utilized as non-traditional biosorbents for pollutant removal.