Comparative Study on the Quality and Antibacterial Activity of Spearmint (Mentha spicata) Leaves and Infusion

In the present study, a comparative investigation between the quality of spearmint leaves and infusion was performed and antibacterial activity against common pathogenic bacteria.Samples (300) represented loose, packed and fresh leaves in addition to their infusions were examined for the microbiological profile and quantitative analyzed for total aflatoxin.Antibacterial activity of spearmint essential oil was determined by disk diffusion method against pathogenic bacteria.Also, moisture content was evaluated.Considering the results obtained, the moisture content was determined as 85, 8.45 and 7.37% in fresh, loose and packed leaves, respectively.Overall, levels of microbial loads were generally exceeded the acceptable levels according to the Egyptian Standards in spearmint leaves, while no detectable microbial counts were found in infusion samples.Although, loose leaves contained the highest microbial load, the fresh leaves contained the lowest with Total Aerobic Viable Bacteria (TAVB) (5.7x10 4 ~5.5x10 7 cfu/g), molds and yeasts count (3.5x10 2 ~8.7x10 3 cfu/g), spore-forming bacteria (9x10 2 ~4.7x10 4 cfu/g), coliform group in MPN (3.2x10 1 ~2.7x10 2 cells/g), Escherichia coli (of positive samples 18~28%) and Bacillus cereus (3.6x10 1 ~1.1x10 2 cfu/g), while Salmonella spp, Shigella spp, Closteridium perfringens and Staphylococcus aureus were not detected.Total aflatoxins (37.32~48.73µg/kg)was detected in loose and packed leaves while was not detected (<5 µg/kg) in fresh leaves and infusion samples.The Gram-positive bacterial count seems to be more susceptible to the investigated essential oil, comparing to the Gram-negative ones.Finally, the study pointed out that spearmint leaves consider hazards which urges the need to provide a health control system, and the importance of spearmint essential oil, as an antimicrobial agent.