*2.2. CSE Preparation*

CS seeds were purchased from First Village Farmer's Union under Hallasan Mountain (Jeju-do, Republic of Korea) in 2018. Seeds were planted for 6 days at 25 ◦C in a dark growth chamber. Sprouts were harvested and freeze-dried (FD 8518; Ilshin Lab Co., Ltd., Dongducheon, Korea) for 3 days. The CSE was obtained by mixing the dried buckwheat sprouts with 90% (*v*/*v*) aqueous methanol. The mixture was ultrasonicated for 30 min and the supernatant was acquired by centrifugation (2232× *g*) for 10 min and filtered through a 0.45-µm polyvinylidene fluoride syringe filter (Millipore, Billerica, MA, USA). The residue was re-extracted once using the procedure described above. The filtrate was evaporated on a rotary evaporator (N-1000; Eyela, Tokyo, Japan) in a water bath at 40 ◦C. The extract

was stored in a deep freezer (WSM-2700UC; Grand Woosung Inc., Seoul, Korea) at −50 ◦C and freeze-dried (FD 8518) for 3 days. All experiments were performed in triplicate.
