Microwave-assisted extraction of Clausena anisata leaves and Vernonia cinerea whole plants to maximize nitrate content: optimization approach, antioxidant activity, and cytotoxicity

Nitrate-rich plants—Clausena anisata leaves and Vernonia cinerea whole plants—are used as smoking cessation aids in Thailand. This work sought to optimize the extraction condition of nitrate from the two plants using microwave-assisted extraction. The Box-Behnken design was applied in this work. Antioxidant activity and in vitro cytotoxicity tests were also evaluated. Three factors including microwave power, duration time, and irradiation cycle, were varied from 300 to 600 W, 10 to 30 s, and 1 to 3 cycles, respectively. Two responses including extraction yield and nitrate content were monitored. Results demonstrated that the low microwave power (300 W) with short duration time (10 s), and low irradiation cycle (one cycle) gave the highest nitrate content. The optimum condition provided extraction yield of 26.0 ± 1.1% and nitrate content of 1.31 ± 0.03% for C. anisata leaves, and extraction yield of 15.9 ± 0.2% and nitrate content of 1.32 ± 0.01% for V. cinerea whole plants. Furthermore, their crude extracts exhibited good antioxidant activity and safety profile. In summary, microwave-assisted extraction was an alternative modern technique for the extraction of nitrate from C. anisata leaves and V. cinerea whole plants. Recently, only V. cinerea was officially included in the National List of Essential Medicines. This work could be used to support the potential of C. anisata leaves as a smoking cessation aid like V. cinerea.