Preliminary Investigation of the Antimicrobial Activities and Synergies of Cinnamaldehyde and ε-Polylysine Hydrochloride
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Abstract:
The intense odor of cinnamaldehyde (CIN) renders its production challenging on an industrial scale. One way to solve this problem is to compound CIN with other active substances. To this end, the antimicrobial activity and synergies of CIN and ε-polylysine hydrochloride (ε-PLH) on four types of foodborne pathogens and two types of spoilage bacteria were studied, with results indicating that both have excellent activity against various pathogens. CIN inhibits fungi better than it does bacteria, with a minimum inhibition concentration (MIC) of 0.05 mg/mL for fungi versus ~0.2 mg/mL for bacteria, while ε-PLH shows the opposite (MIC of ~0.1 mg/mL for bacteria versus 0.2 mg/mL for fungi). Combined CIN and ε-PLH exhibit synergy or partial synergy against Escherichia coli, Listeria monocytogenes, Bacillus cereus, and Staphylococcus aureus, with additive effects against Fusarium oxysporum and Phytophthora litchii. Using CIN with ε-PLH can limit the proliferation of S. aureus and L. monocytogenes and delay the log growth phase of E. coli and B. cereus. In addition, the relative electrical conductivity of bacteria is increased, leading to wrinkled or clumped cell morphologies. Hence, CIN + ε-PLH may exert antimicrobial activity by disrupting the bacterial growth cycle and altering the cell membrane permeability, leading to the leakage of intracellular compounds and changes in the cell morphology that inhibit cell growth or cause cell death. These findings provide theoretical support for the industrial production of essential oils such as CIN.
