Effects of Maturity and Processing on the Volatile Components, Phytochemical Profiles and Antioxidant Activity of Lotus (Nelumbo nucifera) Leaf

In this study, fresh lotus leaves at two maturity stages were processed to tea products by different methods (white-tea process, green-tea process and black-tea process). The volatile compounds, phytochemical profiles and antioxidant activities of lotus-leaf tea were investigated. A total of 81 volatile components were identified with HS-GC-IMS. The mature lotus-leaf tea showed more volatile compounds than the tender lotus-leaf tea. The lotus leaf treated with the white-tea process had more aroma components than other processing methods. In addition, six types of phenolic compounds, including luteolin, catechin, quercetin, orientin, hyperoside and rutin were identified in the lotus-leaf tea. The mature leaves treated with the green-tea process had the highest levels of TPC (49.97 mg gallic acid/g tea) and TFC (73.43 mg rutin/g tea). The aqueous extract of lotus-leaf tea showed positive scavenging capacities of DPPH and ABTS radicals, and ferric ion reducing power, whereas tender lotus leaf treated with the green-tea process exhibited the strongest antioxidant activity. What is more, the antioxidant activities had a significant positive correlation with the levels of TPC and TFC in lotus-leaf tea. Our results provide a theoretical basis for the manufacture of lotus-leaf-tea products with desirable flavor and health benefits.

Automated summary

In this study, lotus leaves were processed into tea products using different methods, and the volatile compounds, phytochemical profiles, and antioxidant activities of the teas were investigated. The mature lotus-leaf tea had more volatile compounds compared to the tender lotus-leaf tea. The white-tea process resulted in a higher amount of aroma components. Various phenolic compounds were identified in the lotus-leaf tea, and the green-tea process on mature leaves showed the highest levels of total phenolic and flavonoid compounds. The lotus-leaf teas exhibited positive antioxidant activities, with the tender leaves processed using the green-tea method showing the strongest activity. The antioxidant activities were positively correlated with the levels of total phenolic and flavonoid compounds in the teas. These findings provide a basis for producing lotus-leaf teas with desirable flavor and health benefits.