Development of a topical applied functional food formulation: Adlay bran oil nanoemulgel
Graphical abstract
Introduction
Adlay bran oil (ABO), obtained from pressing the bran of adlay, or Job's tears (Coix lachrymal-jobi L. var.ma-yuen Stapf), is the main by-product of the adlay refining process. It has good antioxidant, anti-inflammatory, anti-pigmentation, and anti-cancer effects due to its high content of bioactive components (C.-J. Huang et al., 2015). The phytochemical constituents isolated from adlay bran can be divided into nine main categories—namely, phenolic acids, phenolic esters, phenolic aldehydes, flavonoids, triterpenoids, sterols, lactams, lactones, and lignans. (C.-J. Huang et al., 2015). Using ABO to develop health-promoting formulations is desirable because it reduces production waste and increases the economic value of adlay processing.
As the largest organ of the human body, the skin is the most critical barrier involved in preventing the invasion of pathogens as well regulating body temperature. However, the skin is vulnerable to skin cancer, one of the most common cancers worldwide, as well as other diseases. The use of emulsions can enhance the efficacy of bioactive ingredients used to treat the skin diseases. According to previous research, an emulsion is better absorbed when it is processed to a smaller size and is allowed to stay in contact with the skin longer (Pouton, 1985). Therefore, it is desirable to reduce the size of the emulsion droplets and to increase surface retention time when developing emulsion products for skin use.
The formation of an emulsion requires the intervention of an emulsifier to facilitate the uniform dispersion of two immiscible liquids. Selecting a suitable emulsifier can promote the formation of a homogeneous system with better storage stability (Alexander et al., 2013). The stability of an emulsion can be extended by processing it into a gelled system by incorporating a gelling agent (Mohamed, 2004). In this sense, oil-in-water (O/W) or water-in-oil (W/O) emulsions form a macromolecular network structure that prevents the aggregation of the dispersed phase and, thus, improves the stability of the continuous phase. An emulgel is an emulsion mixed with a gelling agent and it is a favorable delivery system for bioactive ingredients when a longer retention time is required (Devada, Jain, Vyas, & Jain, 2011).
Topical administration using delivery systems such as emulsions, ointments, and hydrogels is recommended for many skin problems. However, these topical dosages all have one or more drawbacks, including poor loading concentration, low diffusion coefficient, insufficient stability, and their limitation to the delivery of only hydrophiles or lipophiles. To enhance the functionality of an available topical delivery system, a two-step process that transforms the liquid emulsion into a semisolid emulsion gel has been developed.
Emulgel, a polymeric emulsion system, has the advantages of both an emulsion and a hydrogel system. With the proper design, an emulgel system with a shear thinning property could reproduce not only the excellent stability of a hydrogel, but also the superior skin permeability of liquid emulsions (Devada et al., 2011). The wide variety of gelling agents that are soluble in either oil or aqueous environments allow the encapsulation of both hydrophobic and hydrophilic components in the O/W and W/O emulsions, respectively. Moreover, an emulgel that has a higher viscosity than the liquid emulsion system can increase the retention time of active components on the skin surface and promote better absorption (Mohamed, 2004). Overall, emulgels are a favorable formulation in the percutaneous absorption of both hydrophilic and lipophilic components because they offer alternative phases (dispersed and a continuous), higher skin permeability, better application and storage stability, and the ability to control the release rate.
As bioactives isolated from adlay are effective against many skin-related problems, it is rational and economical to use the oil extracted from adlay bran for skin product development. Specifically, adlay bioactives have been documented to be effective in inhibiting cellular tyrosinase activity and melanin production and, thus, preventing hyperpigmentation, which results from hormonal changes, aging, skin diseases, or injuries (H.-C. Huang, Hsieh, Niu, & Chang, 2014). In this study, an emulsion-based delivery system, including a conventional emulsion (CE) (d > 1 μm), nanoemulsion (NE) (d < 500 nm) (Chime, Kenechukwu, & Attama, 2014; Qian, Decker, Xiao, & McClements, 2012; Zhou, Wang, Cheung, Guo, & Jia, 2008), and nanoemulgel (NG), was prepared and optimized for skin use. The gelling agent selected for the preparation of nanoemulgel system was Pluronic F-127 (PF-127), which is one of the poloxamer ABA block polymer. The special chemical structure of PF-127 makes it more readily soluble in cold than in hot water and, thus, would allow it to maintain a gel-like property at body temperature. The physicochemical properties and percutaneous absorption rate of the prepared skin formulations were then studied systematically. This study is the first to report the production of an emulsion system using ABO. Our results not only demonstrate the potential to re-use a manufacturing by-product but also serve as an excellent reference for selecting a different delivery system for topical applications.
Section snippets
Chemical reagents
Folin-Ciocalteu phenol reagent and sodium carbonate were purchased from Merck (Darmstadt, Germany). Pluronic® F-127 (PF-127), Tween® 80 and Oil red O were obtained from Sigma-Aldrich (St. Louis, MO, USA). Kojic acid was purchased from TCI (Tokyo, Japan). All other chemicals and solvents were of analytical grade. Deionized water was prepared with a Milli-Q water purification system (Millipore, USA).
Preparation of adlay bran oil (ABO)
Adlay (Taichung selective No. 4) cultivated and taxonomically identified by the Taichung District
Construction of pseudo-ternary phase diagram
By constructing a pseudo-ternary phase diagram, all possible mixing ratios of the emulsifier and the organic and aqueous phases were studied systematically, resulting in the elucidation of formulations of various physicochemical properties. Using a titration method, we investigated the existence of a stable emulsion region where the organic phase was composed of 10–90% of the emulsifier (Tween 80) in ABO and was titrated by the aqueous phase (DI water) at various ratios (Fig. 1A). Starting at
Conclusion
We have successfully developed an NG system for topical application. The factors that influence the physical and chemical properties of the product were elucidated. Operational parameters of high-pressure homogenization were investigated to optimize the production process. In addition, the changes in formulation stability due to smaller droplet size and higher viscosity were also examined. Overall, the addition of a gelator, PF-127, to the NE system increased the system viscosity, thus
Declaration of interest
The authors report no conflicts of interest. The authors alone are responsible for the content and writing of this article.
Conflict of interest file
There was no conflict of interest to disclose.
Acknowledgments
This work is supported by the Ministry of Science and Technology, Republic of China (Grant No. 107-2320-B-002-003-MY3 and No. 105-2320-B-002-004-).
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These authors contribute equally.