Both the purchased and the lab-made youtiao samples were
vacuum-dried (DZF-6020, Shanghai, China) at 60 C for 2 h after
shearing into small pieces with a scissor. Approximately 100 g of
dried sample was extracted with 350 ml of n-hexane in an ultrasound
bath for 1 h. The oil sample was obtained after concentrating
the extraction solution with a rotavapour (RE-52AA, Shanghai,
China) at 40 C. The oil samples were placed in sealed glass bottles
and stored in the dark at 4 C before use.