A peppermint oil emulsion stabilized by resveratrol-zein-pectin complex particles: Enhancing the chemical stability and antimicrobial activity in combination with the synergistic effect
Graphical abstract
Introduction
Essential oils (EOs) are naturally-derived aroma compounds obtained from various parts of edible and medicinal plants and exert strong antibacterial and antifungal activity (Donsi & Ferrari, 2016; Seow, Yeo, Chung, & Yuk, 2014). When two or more agents work together, synergism occurs to produce an effect greater than the sum of individual effects, due to their function on one or more different targets in a metabolic pathway (Seow et al., 2014). For example, the combination of cinnamaldehyde with carvacrol showed synergistic antibacterial effects against both Escherichia coli and Staphylococcus aureus (S. aureus) (Ye et al., 2013). A synergistic antibacterial activity against S. aureus was also observed in nisin combined with cinnamaldehyde in pasteurized milk (Shi et al., 2017). The combination of multiple antibacterial agents has become an important approach to enhance the efficiency of antibacterial therapy and overcome resistance to antibacterial agents. However, poor hydro-solubility and high volatility of EOs limit their application in the pharmaceutical, food and cosmetic industries. It is thus necessary to develop the carriers not only to overcome the limitations but also to enhance the antibacterial activity based on the synergistic effect.
Oil-in-water (O/W) emulsions have been considered to be efficient delivery systems for improving water dispersibility of EOs and preventing their interactions with other food ingredients (Donsi et al., 2016; McClements & Li, 2010). However, the oxidative and physical stability of conventional emulsions is limited due to the high interfacial area and a characteristic porous thin interfacial layer (Berton-Carabin, Sagis, & Schroen, 2018; McClements & Decker, 2018). Recently, interfacial engineering of emulsion systems has been developed to improve the oxidative stability by minimizing interactions between pro-oxidants and bioactive lipids (Berton-Carabin, Ropers, & Genot, 2014; McClements & Decker, 2018). A safflower oil emulsion stabilized by lipid droplets coated by milk protein concentrate (MPC) was prepared, showing slower lipid oxidation than conventional emulsions stabilized by MPC alone. (Okubanjo, Loveday, Ye, Wilde, & Singh, 2019). Resveratrol, as an antioxidant co-emulsifier, can be accumulated at the oil-water interface by interacting with proteins to enhance the oxidative stability (Wan, Wang, Wang, Yuan, & Yang, 2014; Wang, Gao et al., 2016). These provide an opportunity not only to improve the oxidative stability of O/W emulsions but also to co-encapsulate bioactive components with different solubility in the single emulsions.
Zein, a major storage protein in corn, contains more than 50% hydrophobic amino acid residues and is soluble in concentrated aqueous ethanol solutions (60–90%) but not in pure water (Shukla & Cheryan, 2001). This property makes zein a suitable material for the encapsulation of bioactive components, such as α-tocopherol, resveratrol and epigallocatechin gallate (Davidov-Pardo, Joye, & McClements, 2015; Donsi, Voudouris, Veen, & Velikov, 2017; Luo, Zhang, Whent, Yu, & Wang, 2011). A Pickering O/W emulsion was successfully produced by bare zein colloidal particles with droplet size in the range of 10–200 μm (de Folter, van Ruijven, & Velikov, 2012). However, the resulting emulsions were unstable against coalescence at low pH due to the poor wettability of the protein. Surface-modified zein particles with water-soluble biopolymers have been utilized to regulate the surface wettability of zein particles and form stable O/W emulsions (Chen et al., 2018; Dai, Sun, Wei, Mao, & Gao, 2018; Feng & Lee, 2016). Pectin, an anionic polysaccharide, belongs to a family of heterogeneous polysaccharides containing mainly α-(1 → 4)-linked partially methyl esterified d-galacturonic acid and rhamnogalacturonan units (Synytsya, Copikova, Matejka, & Machovic, 2003). Zein-pectin core-shell nanoparticles overcome the aggregation problem of bare zein particles and provide better protection for encapsulated molecules than bare zein particles did (Hu et al., 2015; Huang et al., 2017). Additionally, high methoxyl pectin could strongly absorb to the interface of mandarin or lemongrass oil emulsion and improve physical stability against Ostwald ripening (Guerra-Rosas, Morales-Castro, Ochoa-Martinez, Salvia-Trujillo, & Martin-Belloso, 2016).
Peppermint (Mentha piperita) oil is one of the most widely produced and used essential oils in food, flavorings, and pharmaceutical products. Peppermint oil possesses antimicrobial, antiviral and antifungal activities against various types of bacteria and yeasts (Iscan, Kirimer, Kurkcuoglu, Baser, & Demirci, 2002; Mahboubi & Haghi, 2008). Resveratrol, a natural polyphenol, is produced in plants in response to injury and fungal attack (Summerlin et al., 2015). Resveratrol exhibits a broad spectrum of antimicrobial activity across a wide range of microorganisms (Ma et al., 2018), mainly due to the generation of reactive oxygen species causing DNA damage (Subramanian, Soundar, & Mangoli, 2016), oxidative membrane damage (Subramanian, Goswami, Chakraborty, & Jawali, 2014), and metabolic enzyme inhibition (Dadi, Ahmad, & Ahmad, 2009). In this study, resveratrol-fortified zein-pectin particles were prepared to stabilize a peppermint oil emulsion. Physiochemical property of the colloidal particles and emulsions was characterized. Furthermore, antimicrobial efficiency of peppermint oil and resveratrol combination was evaluated against food-borne pathogens.
Section snippets
Materials
Zein (~98%) was purchased from J&K Chemical Co., Ltd. (Shanghai, China). Pectin (50–300 kDa, degree of esterification ≥47.9%) and resveratrol (trans-isomer, ≥98%) were purchased from Sango Biotech Co. (Shanghai, China). Peppermint (M. piperita) oil was obtained from Shanghai Orinno International Business Co., Ltd. (Shanghai, China). The composition of peppermint oil was reported in Table S1. Menthol (≥98%, GC), menthone (≥97%, GC) and Nile red dye were obtained from Sigma-Aldrich Co. (St.
Size and ζ-potential
The size distribution of bare zein particles had a peak around 80 nm (Fig. S1A), which was consistent with a previous report that zein nanoparticles prepared by desolvation method had an average size of 50–200 nm (Kasaai, 2018). The presence of resveratrol at 0.004%, 0.010%, and 0.020% had no impact on the size of zein particles (Fig. S1A). However, a further increase of resveratrol concentration to 0.040% resulted in precipitation to naked eyes. The polyphenol concentration of 0.020% was thus
Conclusions
In the present study, peppermint oil emulsions stabilized by resveratrol-zein-pectin ternary complex particles have been successfully prepared, showing a good encapsulation performance for both resveratrol and peppermint oil. This system has combined the synergistic effect of two antibacterial agents and emulsion-based carrier, which contributes to the improvement of antimicrobial efficiency and chemical stability. These results obtained here should provide the possibility of co-encapsulating
CRediT authorship contribution statement
Hao Cheng: Conceptualization, Investigation, Writing - original draft, Writing - review & editing. Muhammad Aslam Khan: Investigation. Zhenfeng Xie: Investigation. Shengnan Tao: Resources. Yunxing Li: Resources. Li Liang: Conceptualization, Resources, Writing - review & editing, Supervision.
Declaration of competing interest
We wish to confirm that there are no known conflicts of interest associated with this publication and there has been no significant financial support for this work that could have influenced its outcome.
Acknowledgements
This work received supports from the National Natural Science Foundation of China (NSFC Project 31571781), the Fundamental Research Funds for the Central Universities (JUSRP51711B) and the Postgraduate Research & Practice Innovation Program of Jiangsu Province (KYCX17_1411).
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