Antimicrobial activity of extracts from several plant tissues was investigated.The extracts were prepared by conventional and high pressure CO2 extraction (supercritical extraction). The following plants were tested: Ginkgo biloba L. leaves, Nicotiana tabacum L. leaves, green tea (Camellia sinensis L.), green coffee beans (Coffea arabica L.), red onion (Allium cepa L), hops (Humulus lupulus) and guarana seeds (Paullinia cupana). Results showed that different antimicrobial activities were due to the applied solvents and due to the species of a microbe used in study.
Antimicrobial activity of hop extract obtained with supercritical CO2 was tested. The advantages of extraction with supercritical CO2 are mainly in the obtained highly concentrated product, which does not contain side products and most importantly does not contain naturally present bacterial flora. In order to estimate the acid content (alpha- and beta-acids) in the obtained extract an HPLC analysis was performed. Antimicrobial activity was tested by using dilution assay and disc-diffusion assay.