Action mechanism of small and large molecule surfactant-based clove oil nanoemulsions against food-borne pathogens and r
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ORIGINAL PAPER
Action mechanism of small and large molecule surfactant‑based clove oil nanoemulsions against food‑borne pathogens and real‑time detection of their subpopulations Hamid Majeed · John Antoniou · Charles F. Shoemaker · Zhong Fang
Received: 23 July 2014 / Revised: 14 September 2014 / Accepted: 30 September 2014 / Published online: 31 October 2014 © Springer-Verlag Berlin Heidelberg 2014
Abstract Flow cytometry exactly discriminated three subpopulations, i.e., viable, damage and sublethal cells of L. monocytogenes, S. aureus and E. coli when treated at their MIC values. Purity gum ultra (PGU) a large molecule surfactant-based CO nanoemulsion exerted significant impact on cellular subpopulations of L. monocytogenes and S. aureus, with more membrane-damaged cells. On the other hand, when compared with bulk CO the results showed minimum membrane damage and more viable cells, whereas PGU CO nanoemulsion showed minimum effect on cellular subpopulation and represented more viable than damaged cells in case of E. coli. Similarly, Tween 80 a small molecule surfactant-based CO nanoemulsion showed limited overall activity against three tested microorganisms with more viable cells. We conclude that it was due to sequestration of CO constituents in interfaces, less availability in aqueous phase and finally inhibit bactericidal activity. Moreover, both CO and CO nanoemulsions
Communicated by Erko Stackebrandt. Electronic supplementary material The online version of this article (doi:10.1007/s00203-014-1046-3) contains supplementary material, which is available to authorized users. H. Majeed · J. Antoniou · Z. Fang (*) Key Laboratory of Food Colloids and Biotechnology, Ministry of Education, School of Food Science and Technology, Jiangnan University, Wuxi 214122, People’s Republic of China e-mail: [email protected] H. Majeed e-mail: [email protected] C. F. Shoemaker Department of Food Science and Technology, University of California, Davis, CA 95616, USA
showed membrane damage as primary inactivation mechanism of tested bacterial cells. Keywords Flow cytometry · Purity gum ultra · Viable · Sublethal · E. coli · Clove oil
Introduction Nanoemulsions are commercially valuable delivery systems because they have unique characteristics of small size and high surface area, optical clarity, and reduced rate of gravitational separation and flocculation. Common lipid encapsulation systems are emulsions (Rodriguez-Rojo et al. 2012), microencapsulation (Solomon et al. 2012) and liposomes (Mekkerdchoo et al. 2009) where lipids are encapsulated by small and large molecule surfactants. Polysorbate and glycerol esters are defined as small molecule emulsifier, while milk proteins and modified starches have both emulsifying and stabilizing properties known as large molecule emulsifiers (or surface-active polymers). Mao et al. (2009) prepared β-carotene nanoemulsion using small (Tween 20, decaglycerol monolaurate) and large molecule surfactants [octenyl succinate starch (OSS), whey protein isolate (WPI)]. They con
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