Antimicrobial impact of the components of essential oil of Litsea cubeba from Taiwan and antimicrobial activity of the oil in food systems.

Using natural additives to preserve foods has become popular due to consumer demands for nature and safety. Antimicrobial activity is one of the most important properties in many plant essential oils (EOs). The antimicrobial activity of the essential oil of Litsea cubeba (LC-EO) from Taiwan and the antimicrobial impact of individual volatile components in the oil on pathogens or spoilage microorganisms: Vibrio parahaemolyticus, Listeria monocytogenes, Lactobacillus plantarum, and Hansenula anomala in vitro, and the antimicrobial activity of the LC-EO against these organisms in food systems were studied. The "antimicrobial impact" (AI) is a new term that combines the effects of minimal microbicidal concentration (MMC) and quantity of an antimicrobial substance. The AI can quantitatively reflect the relative importance of individual components of the EO on the entire antimicrobial activity of the EO. The MMCs of the LC-EO against V. parahaemolyticus, L. monocytogenes, L. plantarum, and H. anomala were determined as 750, 750, 1500, and 375 μg/g, respectively in vitro. The MMCs of the LC-EO were 3000, 6000, and 12,000 μg/g for L. monocytogenes in tofu stored at 4 °C, 25 °C, and 37 °C, respectively. The temperature affected the bacterial growth which consequently influenced the MMCs of the LC-EO. The MMCs of the LC-EO were 3000, 6000, and 375 μg/g for Vibrio spp. in oysters, L. plantarum in orange-milk beverage, and H. anomala in soy sauce, respectively. Except for soy sauce, the food systems exhibited marked matrix effects on diminishing the antimicrobial activity of the LC-EO. Averagely, citral accounted for ca 70% of the total AI value for all the tested organisms, and the rest of the AI value of the LC-EO was determined by all the tested compounds (ca 4%) and the unidentified compounds (ca 26%).