This work aims to evaluate the antimicrobial potential of ethanolic and water extracts of roselle (Hibiscus sabdariffa), rosemary (Rosmarinus officinalis), clove (Syzygium aromaticum), and thyme (Thymus vulgaris) on some food pathogens and spoilage microorganisms. Agar well diffusion method has been used to determine the antimicrobial activities and minimum inhibitory concentrations (MIC) of different plant extracts against Gram-positive bacteria (Bacillus cereus, Staphylococcus aureus), Gram-negative bacteria (Escherichia coli, Salmonella enteritidis, Vibrio parahaemolyticus, and Pseudomonas aeruginosa), and one fungus (Candida albicans). The extracts exhibited both antibacterial and antifungal activities against tested microorganisms. Ethanolic roselle extract showed significant antibacterial activity (P < 0.05) against all tested bacterial strains, while no inhibitory effect on Candida albicans (CA) was observed. Only the ethanolic extracts of clove and thyme showed antifungal effects against CA with inhibition zones ranging from 25.2 ± 1.4 to 15.8 ± 1.2 mm, respectively. Bacillus cereus (BC) appears to be the most sensitive strain to the aqueous extract of clove with a MIC of 0.315%. To enhance our understanding of antimicrobial activity mechanism of plant extracts, the changes in internal pH (pH_int), and membrane potential were measured in Staphylococcus aureus (SA) and Escherichia coli (EC) cells after exposure to the plant extracts. The results indicated that the plant extracts significantly affected the cell membrane of Gram-positive and Gram-negative bacteria, as demonstrated by the decline in pH_int as well as cell membrane hyperpolarization. In conclusion, plant extracts are of great value as natural antimicrobials and can use safely as food preservatives.

Aims This study aims to assess the removal mechanism of patulin using heat-treated Saccharomyces cerevisiae cells and identify the role of different cell wall components in the binding process. Methods and Results In order to understand the binding mechanism, viable cells, heat-treated cells, cell wall and intracellular extract were performed to assess their ability to remove patulin. Additionally, the effects of chemical and enzymatic treatments of yeast on the binding ability were tested. The results showed that there was no significant difference between viable (53·28%) and heat-treated yeast cells (51·71%) in patulin binding. In addition, the cell wall fraction decreased patulin by 35·05%, and the cell extract nearly failed to bind patulin. Treatments with protease E, methanol, formaldehyde, periodate or urea significantly decreased (P < 0·05) the ability of heat-treated cells to remove patulin. Fourier transform infrared (FTIR) analysis indicated that more functional groups were involved in the binding process of heat-treated cells. Conclusions Polysaccharides and protein are important components of yeast cell wall involved in patulin removal. In addition, hydrophobic interactions play a major role in binding processes. Significance and Impact of the Study Heat-treated S. cerevisiae cells could be used to control patulin contamination in the apple juice industry. Also, our results proof that the patulin removal process is based mainly on the adsorption not degradation.