Phenolic contents and antioxidant properties of Stenochlaena palustris, an edible medicinal fern

Stenochlaena palustris is an edible fern that is used as vegetable and in traditional medicine. This study assessed the total polyphenol, flavonoid, hydroxycinnamic acid and anthocyanin contents, as well as radical scavenging, ferric reducing and metal chelating activities of the extracts of S. palustris. The four extracts analysed were prepared from the young sterile, mature sterile, young fertile, and mature fertile fronds of the fern. The extract of mature sterile frond had the highest contents of total polyphenols (51.69 mg/g dry matter), flavonoids (58.05 mg/g dry matter), and hydroxycinnamic acids (48.80 mg/g dry matter). The extract of the edible young sterile frond contained 20-fold more anthocyanins (51.32 mg/100 g dry matter) compared with the other extracts. Overall, total polyphenol contents correlated strongly and positively with radical scavenging activity (R-2=0.968) and ferric reducing activity (R-2=0.960), but only moderately with metal chelating activity (R-2=0.446). Anthocyanin content and high specific metal chelating activity of the edible young sterile frond highlight the potential of the fern as a functional food. On the other hand, the mature sterile frond, with its high phenolic contents, potent effectiveness as reductants and year-round availability, represents a potential source of natural antioxidants.