Effect of extraction methods on the antioxidant properties of water hyacinth, Eichhornia crassipes

Water hyacinth, Eichhornia crassipes, is a pharmaceutical aquatic plant that has created many environmental problems due to its being non-native to Anzali Wetland in Iran. This study aimed to compare the antioxidant activities of the leaf, stem, and root extracts of water hyacinth prepared by solvent extraction (SE), and ultrasound-assisted extraction (UAE) methods. The extraction process in the UAE method was performed using a water bath ultrasound device at a frequency of 42 kHz and a power of 70 watts in 60 min. The total phenol content, DPPH radical scavenging activity, total antioxidant capacity, and ferric-reducing antioxidant power in different extracts were evaluated. The highest amounts of total phenol contents in both SE and UAE methods were related to the water and water/ethanol extracts of the leaf (27.32 ± 0.24 and 25.29 ± 1.49 µg GAE/g DW, respectively) by the UAE method which did not exhibit significant differences with the water extract of the leaf by SEM (p > 0.05). The water/ethanol, and ethanol leaf extracts by the UAE method (0.84 ± 0.02, and 0.77 ± 0.03%), and the water leaf extract by SE method (0.76 ± 0.05) respectively displayed the highest free radical scavenging activity which did not show significant differences with the water leaf extract by UAE method, the water/ethanol, ethanol leaf extracts by SE method, and the water stem extract by UAE method (p > 0.05). In addition, in the total antioxidant capacity assay, the water/ethanol extracts of the leaf (27.75 ± 1.74 and 26.88 ± 3.73 30 mg AAE/g DW) respectively by UAE and SE methods showed the highest amounts of total antioxidant capacity exhibiting significant differences from other treatments (p < 0.05). On the other hand, the highest amounts of the ferric reducing antioxidant power were related to the water leaf extract by SE method (73.06 ± 13.30 mg AAE/g DW) and the water/ethanol, ethanol leaf extracts by UAE method (70.95 ± 2.47 and 69.42 ± 8.40) respectively displayed significant differences from other treatments (p < 0.05). In general, the UAE method was more efficient than the SE method. In addition, water/ethanol solvent with a ratio of 50:50 was the best solvent for extracting in the UAE method. According to the results, the invasive water hyacinth plant was found to be a suitable option for the extraction of natural antioxidant compounds. Moreover, the extract of this plant can be used as a natural preservative to increase the shelf life of seafood products.