Characterization of phenolic compounds from normal ginger (Zingiber officinale Rosc.) and black ginger (Kaempferia parviflora Wall.) using UPLC-DAD-QToF-MS

Zingiberaceae is the large diverse family comprised of rhizomatous plants with a higher concentration of phenolic compounds. The normal ginger (Zingiber officinale Rosc.) and black ginger (Kaempferia parviflora Wall.) belongs to this family and have similar morphological characteristics of rhizome, but their phenolic composition revealed differently. On this study, the phenolic composition of normal ginger (from Ethiopia and Korea) and black gingers (from Korea and Thailand) were profiled using ultra performance liquid chromatography coupled with diode array detector, quadrupole time-of-flight mass spectrometry (UPLC-DAD-QToF-MS). The result revealed that gingerol-related phenolic acid was detected only in normal gingers while, the methoxyflavones were identified exclusively in black gingers. 6-gingerol, 8-gingerol, 10-gingerol, 1-dehydro-6-gingerdione, and diacetoxy-8-gingerdiol were the major constituents among 18 phenolic acids detected from normal gingers, and 3,5,7,3,4-pentamethoxyflavone and 5,7,4-trimethoxyflavone were confirmed as predominant constituents among 13 methoxyflavones from black gingers. The total phenolic content was 434.7 and 698.1mg/100g dry weight (DW) in Korean and Ethiopian sample, respectively. The total methoxyflavone concentration was 4388.0mg/100g DW and 3940.2mg/100g DW in Korean and Thai black ginger sample, respectively. The higher concentration of methoxyflavones is from advanced biosynthetic pathway related to accumulated color of black ginger. In addition, new possible structural fragmentation was proposed for gingerol homologous series as additional pathway under the positive ionization mode, and further rationalized that ferulic acid moiety is the biosynthetic precursor. The result suggested that despite the morphological similarity, normal and black ginger showed distinct biosynthetic difference to synthesis their major secondary metabolites.