Antimicrobial activity of honeybush (Cyclopia intermedia) ethanol extract against foodborne pathogens and its application in washing fresh-cut Swiss chard

Abstract

This study aimed to determine the antimicrobial activities of honeybush ethanol extract (HBE) against Listeria monocytogenes and Escherichia coli O157:H7, and to define whether it could be used to wash fresh-cut Swiss chard. HPLC analysis showed that HBE contained the phenolic compounds, hesperidin, luteolin, kaempferol, mangiferin, and epicatechin, indicating potential antimicrobial activities. The results of disc diffusion tests, time-kill assays, and analyses of the released intracellular compounds revealed that HBE was more effective against L. monocytogenes than E. coli O157:H7. Moreover, scanning electron microscopy images showed that HBE damaged and shriveled the cells of both pathogens. Washing fresh-cut Swiss chard spiked with L. monocytogenes and E. coli O157:H7 with HBE (6 mg/mL) resulted in 2.31–2.67 log reductions in the populations of these bacteria compared with those in the controls. These results were similar to those of washing with sodium hypochlorite (2.20–2.58 log reduction). In addition, washing with HBE maintained the marketable qualities of fresh-cut Swiss chard, namely, color, texture, and electrolyte leakage rates that indicated tissue deterioration. In contrast, the electrolyte leakage rate of the samples washed with sodium hypochlorite increased. These results indicate that HBE could replace sodium hypochlorite and serve as a novel washing agent to ensure the safety and quality of fresh-cut leafy vegetables.