Characteristic volatile fingerprints of three edible marine green algae (Ulva spp.) in China by HS-GC-IMS and evaluation of the antioxidant bioactivities

•The volatile compounds of three Ulva spp. were investigated by HS-GC-IMS.•A total of 101 volatile compounds had been detected in three Ulva samples.•Ulva samples could be distinguished clearly by HS-GC-IMS coupled with PCA.•The in vitro antioxidant capacity of different Ulva spp. extracts was evaluated.•TFC and TPC were correlated to the antioxidant capacity of Ulva spp.