Evaluation of antimicrobial activities of plant extracts of in vitro cultures of selected microorganisms relevant to food - part A: rooibos

Antimicrobial effects of an extract out of fermented rooibos (Aspalathus linearis) on lactic acid bacteria (Lactobacillus spp., Carnobacterium spp., Leuconostoc carnosum), food spoilage organisms (Bacillus spp., Brochothrix spp., Pseudomonas fluorescens) and foodborne pathogens (Listeria monocytogenes, Salmonella Enteritidis) were evaluated. The microorganisms were inoculated in nutrient broth to reach an initial contamination dose of 2-3 log cfu/ml. 5 mg/ml rooibos extract was added. During storage at 10 degrees C and 25 degrees C for 28 days the growth of bacteria was monitored directly before adding the rooibos and on day 1, 7, 14, 21 und 28 after adding. Rooibos extract had a statistically verified antimicrobial activity on Listeria monocytogenes at 10 degrees C within the first 14 days. There was no antilisterial effect at 25 degrees C. A sensitivity of the extract against lactic acid bacteria (reduction by one log unit) after one week of storage at 10 degrees C persisted to the end of the investigation. The partly detected inhibited growth of food spoilage organisms within the first 24 hours at both temperatures and lactic acid bacteria at 25 degrees C respectively was not statistically significant. There was no antibacterial activity on Salmonella Enteritidis detectable.