In recent years, aromatic plants and their extracts have been examined for their effectiveness for food safety and preservation applications (Prakash, Kedia, Mishra, & Dubey, 2015) and have received attention as growth and health promoters (Brenes & Roura, 2010). Most of their properties are due to their essential oils and other secondary plant metabolite components. Phytochemicals, such as essential oils, contain a complex mixture of nonvolatile and volatile compounds produced by aromatic plants as secondary metabolites which have antioxidant, antiradical, and antimicrobial properties (Bakkali, Averbeck, Averbeck, & Idaomar, 2008), and are classified by the United States Food and Drug Administration as generally recognized as safe (GRAS) (Weiss, Gaysinsky, Davidson, & McClements, 2009). They have been widely used as functional ingredients in food, cosmetic, and pharmaceutical applications (Cimanga et al., 2002). For example, thyme oil has been shown to have inhibitory activities against various bacteria and yeasts (Gaysinsky, Davidson, McClements, & Weiss, 2008). However, direct incorporation of essential oils in food systems encounters many challenges due to their low water solubility and interactive binding with food components such as protein and lipids, which limits their utilization in aqueous-based foods and beverages.
In order to expand the use of essential oils, a feasible way to improve essential oils dispersibility was to encapsulate essential oil within emulsion-based delivery systems. Emulsions are unstable system that consist of at least two incompatible liquids, whereby one of these liquids is dispersed in the other liquid in droplet-form. Emulsions tend to decompose over time through various occurrences, such as flocculation, coalescence, partial coalescence, or Ostwald ripening (Robins, 2000). Therefore, emulsifiers have been employed to promote the formation of dispersions by reducing the interfacial tension, and to prevent coalescence and flocculation of droplets by creating a net repulsion between the droplets (Dickinson). Generally, these emulsifiers can be broadly classified into three types: (i) Small molecular emulsifiers such as phospholipid (Pichot, Watson, & Norton, 2013), and Saponins (Gutiérrez et al., 2008); (ii) biological macromolecular emulsifiers such as proteins (Joshi et al., 2012), polysaccharides (Xiangyang Li, Al-Assaf, Fang, & Phillips, 2012), and starch (Charoen et al., 2011); (iii) colloidal particles, such as protein aggregates (Liu & Tang, 2013), and protein/polysaccharide colloidal particles (Santos, Calero, Guerrero, & Muñoz, 2015). In these emulsifiers, cellulose has had received considerable scholarly attention. Cellulose obtained via physical and chemical methods has attracted increasing interest in the fields of food, pharmaceutics, energy and chemicals research
most widespread and abundant natural biological resources, but also it has superior properties (including biocompatibility, biodegradable, nanoscale effect, high strength and strong surface activity) compared with inorganic nanoparticles. Cellulosic materials can also be hydrophobized to form food grade emulsions. Cellulose nanofibrils, cellulose nanocrystals, modified cellulose (TEMPO oxidized cellulose, OSA-modified cellulose) were used to reduce the lipid oxidation rate and improved
the stability of functional component (Chen et al., 2018; Kargar, Fayazmanesh, Alavi, Spyropoulos, & Norton, 2012; Lu, Zhang, Li, & Huang, 2018; Zhou et al., 2018). But the mean particle diameter of emulsions reached a few microns or even a dozen microns, and the emulsions showed varying degree of instability. Meanwhile, the essential oil had good solubility in the aqueous phase it often induced Ostwald ripening. Thus, how to use cellulose particles to prepare nanoscale essential oil emulsions, promoted their stability and improved their bioavailability, that was a new challenge.
In this study, the thyme oil emulsion was prepared using a novel type of spherical cellulose suspension. The effect of different cellulose structures on the interfacial adsorption properties of emulsion and loading efficiency and retention rate of thyme oil were analyzed. The objective was to reveal the relationship between cellulose structure and the adsorption properties at oil-in-water interface. These results could provide useful data for the stability and transportation of essential oils.