Effect of Different Solvents on the Extraction of Compounds from Different Parts of Undaria pinnatifida (Harvey) Suringar

Asian kelp (Undaria pinnatifida) is a brown alga mainly grown and consumed in East Asian countries such as China, Japan, and Korea. To date, studies on the various biological activities of Asian kelp have been conducted; however, studies focusing on the different parts of Asian kelp and their use for other than food are limited. Therefore, in this study, different parts of Asian kelp, namely, whole U. pinnatifida (UP), U. pinnatifida blade (UPB), U. pinnatifida stipe (UPS), and U. pinnatifida sporophylls (UPSP), were extracted by using different solvents including ethanol, methanol, and hot water. The antioxidant activity, antiaging effect, and phenolic content of the extracts were investigated. The results revealed that the UPB methanolic extract had significantly higher polyphenol and flavonoid contents, with the respective values of 5.61 mg TAN/g and 7.80 mg QUE/g, than the other extracts. The DPPH and ABTS radical scavenging activities and FRAP values were the highest in the 95% ethanolic (IC50 12.73 mg/mL), methanolic (63.83%), and ethanolic (75.75%) extracts of UPB, respectively. Superoxide dismutase, catalase, and ascorbate peroxidase enzymatic activities were also measured, and the results showed that the activities of these enzymes were higher in the UPB methanolic extract than in the other extracts. Similarly, the highest elastase and tyrosinase inhibitory activity was observed in the UPB methanolic extract. The highest phenolic content was found in the hot water extract of UP (4-hydroxybenzoic acid) and the ethanolic extracts of all parts (naringin and naringenin). The phenolic content of the Asian kelp differed depending on the parts and extraction solvents used. Finally, the antioxidant activity of the UPB extract showed a close correlation with the polyphenol and flavonoid contents. The methanol extract of UPB exhibited excellent antioxidant and antiaging activities, indicating its potential use in the development of functional materials using Asian kelp and in other new applications.