Chemical composition and antibacterial activity of essential oils and major fractions of four Achillea species and their nanoemulsions against foodborne bacteria
Graphical abstract
Introduction
In the recent years, food safety issue has become one of the main public health concerns. Despite the high degree of awareness of food preservation methods, there is an increase in the occurrence of disease outbreaks caused by pathogenic and spoilage microorganisms in foods (Hu, Renly, Edlund, Davis, & Kaufman, 2016). It is estimated that up to 30% of the population in industrialized countries suffer from a foodborne disease each year (Newell et al., 2010). In the United States, there are 31 species of pathogens causing 9.4 million cases of food-borne illnesses each year (Scallan et al., 2011). We can assume that the prevalence of foodborne diseases in the developing world is even higher (Hanson et al., 2012, Henao et al., 2015), although it is difficult to obtain the data that would support this assumption. The use of natural antimicrobial compounds in food has gained considerable attention by consumers and the food industry. This is primarily due to the misuse and mishandling of chemical antimicrobial agents that have resulted in a dramatic rise of a group of microorganisms including foodborne pathogens that are not only antibiotic resistant but also more tolerant to several food preservation methods. In addition, increasing consumers' awareness of the potential negative impact of synthetic preservatives on health versus the benefits of natural additives has prompted researchers to explore new alternatives in food preservation that reduce disease incidence and avoid negative impacts on human health (Gyawali & Ibrahim, 2014). Among promising alternative methods-such as biological control and active packaging-aromatic plants have been examined as potential inhibitors against a wide array of pathogenic microorganisms including the foodborne and food spoilage bacteria and most of their properties have been linked to their contents of EOs (Burt, 2004, Calo et al., 2015). Natural occurrence of EOs as part of the human diet also suggests low toxic problems. However, the performance of plant-based products, including EOs as antimicrobial agents is inadequate for major practical use due to limitations associated with extraction, formulation and application. The urgent need now is the search for innovative techniques for developing and strengthening the use of phytochemicals as natural antimicrobials with high safety margins. In this context, nanotechnology has emerged as a new field of interdisciplinary research on particles of size 50–200 nm (Tadros, Izquierdo, Esquena, & Solans, 2004) and dedicated to the creation, improvement and utility of nanoscale structures for biological bioassays. The growing number of their promising applications in material science, pharmacology and medicine causes the increasing interest in nanostructures, including nanoemulsions. When transformed into nanoparticles, materials could acquire novel general and biological properties, show increased affinity to the target, penetrate rapidly and selectively accumulated in various types of cells (Oberdörster, Oberdörster, & Oberdörster, 2005). The genus Achillea (Family: Asteraceae) is one of the most important genera of the Asteraceae family comprising about 115 species, widespread over the Northern hemisphere mostly in Europe, Asia, North America and the Middle East (Candan et al., 2003). Besides reports concerning the traditional uses of different species of the genus Achillea, pharmacological activities of extracts and essential oils of Achillea plants, including antioxidant, analgesic, anti-inflammatory, and antimicrobial activities have been well-confirmed (Candan et al., 2003, Nenaah, 2014). To expand the knowledge about the medical applications of the Egyptian Achillea plants, the current study aimed to determine the chemical composition and the antibacterial activity of EOs of Achillea biebersteinii, Achillea fragrantissima, Achillea santolina and Achillea millefolium and their major fractions against five species of foodborne bacteria. We also developed new nanoemulsion formulations from EOs and tested their antibacterial activity.
Section snippets
Test bacteria
Two Gram-positive and three-Gram negative foodborne and food spoilage bacteria from the American Type Culture Collection (ATCC) were included in the current study. Gram-positive: Listeria monocytogenes ATCC 7644 and Staphylococcus aureus ATCC 25923. Gram-negative: Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853 and Salmonella enteritidis ATCC 13076. Stock cultures of bacteria were grown in Mueller-Hinton agar broth (MHA, Oxoid) at 37 °C for 18–24 h before using in bioassays.
Collection and preparation of the test plants and extraction of essential oils EOs
The
Chemical composition of EOs
The yield of Achillea EOs were 0.88, 0.76, 0.49 and 0.21%, for A. fragrantissima, A. biebersteinii, A. santolina and A. millefolium, respectively. Chemical composition analysis revealed that cis-thujone (28.4%), 2, 5-dimethyl-3-vinyl-4-hexen-2-ol (Santolina alcohol) (16.1%), 3, 3, 6-trimethyl-1, 5-heptadien-4-one (Artmisia ketone) (14.8%) and trans-thujone (12.5%) were the major constituents of A. fragrantissima oil. The oil of A. biebersteinii contains, mainly cis-ascaridol (33.8%), Р-cymene
Discussion
There are similarities in the chemical composition of EOs with previous studies regarding the same species growing in Egypt or elsewhere (Bader et al., 2003, Candan et al., 2003, El-Shazly et al., 2008, Azizi et al., 2010). Slight differences were also observed both in the composition and percentage of the major fractions of certain species such as A. biebersteinii (Rahimmalek et al., 2009), A. santolina (Mohamed & Abdelgaleil, 2008) and A. millefolium (Bimbiraitė, Ragažinskienė, Maruška, &
Conclusion
The test plant oils and their nanoemulsions showed a promising antibacterial activity against certain foodborne bacteria. These natural products can represent a step forward in the search for novel antibacterial agents, at a time when there is an urgent need for novel drugs with no or minimal side effects. Nevertheless, further studies should be conducted to establish various limitations about their mammalian safety, antimicrobial mode of action and appropriate formulations for utilization as
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