Mechanism and Stability of Antimicrobial Activity of Zingiber cassumunar Roxb. Rhizome Extract Against Foodborne Pathogenic Microorganisms

Zingiber cassumunar Roxb. rhizome extract has high potential as an antimicrobial agent, which can be applied in various food production processes and plays role in inhibiting various foodborne pathogenic microorganisms. The purpose of this research was to study the mechanism and stability of the extract’s antimicrobial activity, especially when observed from the degradation of microbial cells. Specimens were extracted by maceration method with three types of solvents with different polarities and steam distillation. The 25% extract using ethyl acetate solvent showed antimicrobial activity against Gram-negative bacteria (Enterobacter spp. and Pseudomonas spp.); Gram-positive bacteria (Listeria monocytogenes); and fungi (Rhizopus oryzae and Penicillium spp.) in well-diffusion assays. The antimicrobial activity of the extract was lower than several commercially used antibiotics such as antibacterial (penicillin G and streptomycin) and antifungal (nystatin) but exhibited broad inhibition spectrum against pathogen samples. The antimicrobial activity of the extract will increase at a low pH condition (pH 4–5) and is stable in 1–4% salt solution. Although the inhibitory activity was decreased slightly upon heating, the antimicrobial activity was stable up to 15 min of exposure to high temperatures (80^○C and 100^○C). Antimicrobial activity of the extract was reported to be higher in a spheroplast and protoplast condition. Leakage of metal ions such as calcium and potassium ions indicated that the activity of the extract could interfere with cell permeability so that the cells become lysed. The extract caused some damage to the bacteria and fungi cell bodies such as holes, curls, shrinkage, elongation, and swelling. Graphical Abstract: (Figure presented.)