Screening of the volatile compounds in fresh and thermally treated watermelon juice via headspace-gas chromatography-ion mobility spectrometry and comprehensive two-dimensional gas chromatography-olfactory-mass spectrometry analysis

Previously, the aroma compounds in watermelon juice were analyzed by either GC-MS or GC-O. These methods could not extract and analyze the volatile compounds comprehensively. Compared to the previous studies, for accurately identifying the aroma profile, the volatile compounds in fresh watermelon juice (FW) and thermally treated watermelon juice (TW) were analyzed using HS-GC-IMS and GC × GC-O-MS. Twenty-three compounds were detected by HS-GC-IMS, among them, allyl methyl sulfide, acetoin, and pentanal were identified for the first time in TW. Through GC × GC-O-MS analysis, 130 and 140 compounds were detected in FW and TW, respectively, and 36 and 38 of these compounds were smelled. In this study, 2,6-dimethyl-5-heptenal was identified for the first time in FW as an odor-contributing compound. These two kinds of juices could be differentiated by heat-mapping. The concentrations of ( E )-2-decenal, decanal, 2-hexenal, 2-pentylfuran, and 6-methyl-5-hepten-2-one increased greatly by Volcano plot, and they contributed to the off-flavor in TW. For aroma analysis of watermelon juice, HS-GC-IMS can rapidly analyze the samples with low detection limits without pretreatment, while GC × GC-O-MS can precisely identify the compounds with sniffing. The results of this study suggest that HS-GC-IMS and GC × GC-O-MS can analyze the aroma profile more comprehensively and discriminate FW and TW more efficiently. • HS-GC-IMS and GC × GC-O-MS were applied to analyze volatiles in watermelon juice. • Allyl methyl sulfide and 3-hydroxy-2-butanone were identified in heated juice first. • 2,6-Dimethyl-5-heptenal was identified in fresh juice first.