Discovery of 1’-acetoxychavicol acetate (ACA) as a promising antibacterial compound from galangal (Alpinia galanga (Linn.) Willd)

Galangal (Alpinia galanga (Linn.) Willd) is a perennial aromatic rhizomatous plant with great industrial importance. In this study, four major antibacterial compounds were isolated from galangal and further identified as hydroxycinnamaldehyde, cinnamaldehyde, coumaryl alcohol, and 1′-acetoxychavicol acetate (ACA). Among them, ACA was a less investigated antibacterial compound in galangal, with minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) 0.313 and 0.625 mg/mL, respectively, against multidrug-resistant Staphylococcus aureus SJTUF 20758. The mechanism study found that ACA significantly influenced the bacterial morphology and damaged the bacterial cell membrane integrity. Furthermore, quantitative proteomic analysis indicated that ACA at sub-MIC, on one hand, inhibited the expression of proteins associated with cell wall and membrane synthesis, osmotic regulation, and bacterial adhesion and invasion. On the other hand, it increased the expression of proteins pertinent to oxidative stress response, respiratory chain, and ATP synthesis. Therefore, ACA might initially target cell membrane by changing the expression of key membrane proteins involved in maintaining normal cell membrane functions, leading to the damage of cell membrane integrity, and also might trigger the survival response of bacteria. In general, to the best of our knowledge, it is for the first time to clarify the antibacterial mechanism of ACA. In addition, galangal is a promising spice rich in antibacterial compounds, especially ACA, which may be used as natural preservatives in the food industry.