Journal of Taiwan Agricultural Research

Fig. 1.　The tested leafy sweetpotato cultivars included (A) ‘Purple Leaf’ (PL), (B) ‘Fancy Leaf’ (FL), and (C) full-fermented leaf tea sample (FFLT) processed at a ratio of 2 : 1 of the leaves PL and FL cultivars.

Author:Ya-Lin Lee*, Che-Lun Huang, Tzu-Huan Hung, Wei-Ting Liu, Su-Yue Lin, Chiu-Hua Chen, Yi-Han Ho, Ying-Fu Lee, and Chung-En Tseng

Abstract:

Two cultivars of leafy sweetpotato (Ipomoea batatas L.), ‘Purple Leaf’ (PL) and ‘Fancy Leaf’ (FL), were mixed (at a ratio of 2 : 1) and processed to produce a full-fermented leaf tea (FFLT). Two harvests of the leafy tissues were collected to study their bioactive phytochemicals and physiological activities. The first harvest was conducted in the winter (collected on 2021/11/16), and the second was in the autumn (2022/09/01). The materials of the former were divided into leaf blade and petiole portions. Extracts with room-temperature distilled water (ddH₂O) were conducted to examine the total phenolics and flavonoids contents, and the reducing power was analyzed to reveal their antioxidative activities. Results showed that the nutritional values of the leaf blade tissues were much higher than those of the petioles. The FFLT samples made from both harvests were prepared with boiling ddH₂O and showed similar reducing power. In contrast, the flavonoid content of the harvest in the autumn was 1.7 times that of the winter, but the latter was slightly higher in the phenolic content than the former. The physiological activity was studied with the FFLT prepared from the second harvest, and its raw material of the leaf tea (RMLT) was also extracted with boiling ddH₂O for comparison. Results showed that both FFLT and RMLT extracts exhibited anti-inflammatory activity by reducing nitric oxide (NO) production; however, the latter increased TNF-α production (a detrimental response), while the former did not. In inhibiting protein glycation, both extracts showed effectiveness, with the FFLT being more effective than the RMLT. These results suggest that the full-fermentation manufacturing process converts certain phytochemicals in sweetpotato leaves to enhance their bioactivity, thereby making the resulting leaf tea a potential food with improved health benefits.

Key words:Leafy sweetpotato, Total phenolics, Total flavonoids, Anti-inflammation, Anti-glycation