Article Cite This: J. Agric. Food Chem. 2019, 67, 11066−11076 pubs.acs.org/JAFC Molecular Encapsulation of Cinnamaldehyde within Cyclodextrin Inclusion Complex Electrospun Nanofibers: Fast-Dissolution, Enhanced Water Solubility, High Temperature Stability, and Antibacterial Activity of Cinnamaldehyde † † † § † ‡ Zehra I. Yildiz, Mehmet E. Kilic, Engin Durgun, , and Tamer Uyar*, , † Institute of Materials Science & Nanotechnology, Bilkent University, Ankara 06800, Turkey ‡ Department of Fiber Science & Apparel Design, College of Human Ecology, Cornell University, Ithaca, New York 14853, United States § UNAM-National Nanotechnology Research Center, Bilkent University, Ankara 06800, Turkey *S Supporting Information ABSTRACT: The electrospinning of nanofibers (NFs) of cinnamaldehyde inclusion complexes (ICs) with two different hydroxypropylated cyclodextrins (CDs), hydroxypropyl-β-cyclodextrin (HP-β-CD) and hydroxypropyl-γ-cyclodextrin (HP-γ- CD), was successfully performed in order to produce cinnamaldehyde/CD-IC NFs without using an additional polymer matrix. The inclusion complexation between cinnamaldehyde and hydroxypropylated CDs was studied by computational molecular modeling, and the results suggested that HP-β-CD and HP-γ-CD can be inclusion complexed with cinnamaldehyde at 1:1 and 2:1 (cinnamaldehyde/CD) molar ratios. Additionally, molecular modeling and phase solubility studies showed that water solubility of cinnamaldehyde dramatically increases with cyclodextrin inclusion complex (CD-IC) formation. The HP-β-CD has shown slightly stronger binding with cinnamaldehyde when compared to HP-γ-CD for cinnamaldehyde/CD-IC. Although cinnamaldehyde is a highly volatile compound, it was effectively preserved with high loading by the cinnamaldehyde/CD-IC NFs. It was also observed that cinnamaldehyde has shown much higher temperature stability in cinnamaldehyde/CD-IC NFs compared to uncomplexed cinnamaldehyde because of the inclusion complexation state of cinnamaldehyde within the hydroxypropylated CD cavity. Moreover, cinnamaldehyde still has kept its antibacterial activity in cinnamaldehyde/CD-IC NF samples when tested against Escherichia coli. In addition, cinnamaldehyde/CD-IC NF mats were fast-dissolving in water, even though pure cinnamaldehyde has a water-insoluble nature. In brief, self-standing nanofibrous mats of electrospun cinnamaldehyde/CD-IC NFs are potentially applicable in food, oral-care, healthcare, and pharmaceutics because of their fast-dissolving character, enhanced water solubility, stability at elevated temperature, and promising antibacterial activity. KEYWORDS: cinnamaldehyde, cyclodextrins, cyclodextrin inclusion complexes, electrospinning, nanofibers, fast-dissolving, water solubility, high temperature stability, antibacterial activity Downloaded via BILKENT UNIV on November 19, 2019 at 19:35:31 (UTC). ■ INTRODUCTION relatively low water solubility; therefore, the native CDs are fi Molecular encapsulation of active agents and functional chemically modi ed to increase their solubility by substituting additives by cyclodextrins (CDs) has been quite practical in some of the primary and/or secondary hydroxyl groups by See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles. hydroxypropyl (HP) groups (Figure 1a), methyl groups, or the food, pharmaceutical, and cosmetic industries because the 7,8 CD-encapsulated molecules can be protected from heat, light, sulfobutyl groups, and so forth. moisture, oxygen, or other extreme conditions, thus enhancing The electrospinning (Figure 1b) technique is commonly used to produce microfibers and nanofibers (NFs) from a the stability, shelf-life, and bioavailability of the active − − 9 19 molecules.1 4 CDs which are cyclic oligosaccharides have a variety of polymeric and nonpolymeric materials. The fi cone-shaped molecular structure with a hydrophobic cavity unique properties of electrospun nano brous materials such as fl which makes them attractive host molecules for the host− nanoporous structure, very large surface area, design exibility, guest-type inclusion complexes (ICs), especially with nonpolar and lightweight enable their use in many applications such as 5 food, textiles, membranes/filters, sensors, biotechnology, compounds. CDs are currently used in food formulations and 9−13 pharmaceutical and cosmetic products for the solubility agriculture, composites, and energy. In general, polymeric fi increase, protection, and the delivery of active agents. CDs materials are used to obtain electrospun brous materials also provide controlled release in active packaging6 and they because long polymeric chains provide certain chain are classified as GRAS (Generally Recognized As Safe) by the U.S. Food and Drug Administration. There are mainly three Received: May 4, 2019 classes of native CDs having six (α-CD), seven (β-CD), and Revised: July 7, 2019 eight (γ-CD) glucopyranose units linked by α-(1,4) linkage in Accepted: September 11, 2019 their molecular structure. These three native CDs have Published: September 11, 2019 © 2019 American Chemical Society 11066 DOI: 10.1021/acs.jafc.9b02789 J. Agric. Food Chem. 2019, 67, 11066−11076 Journal of Agricultural and Food Chemistry Article cinnamaldehyde has certain shelf-life problems due to its high volatility, low stability, low solubility, and sensitivity to oxygen, light, and heat.34,35 Yet, molecular encapsulation of cinnamal- dehyde with cyclodextrin inclusion complexation is one of the promising approaches in order to eliminate the above- mentioned drawbacks of cinnamaldehyde. For example, it was shown that enhancement of photostability and thermo- stability of cinnamaldehyde after complexation with γ-CD derivatives was possible.36 In another related study, inclusion complexation between cinnamaldehyde and β-CD resulted in prevention of cinnamaldehyde from oxidation; besides, the cinnamaldehyde/β-CD ICs showed antioxidative properties similar to pristine cinnamaldehyde.37 Moreover, the antimicro- bial active packaging was designed by using ICs of cinnamaldehyde with β-CD in which improved stability and controlled release of cinnamaldehyde was obtained.38 In the study of Sun et al., the inclusion mechanism and structures of cinnamaldehyde with different cyclodextrins were investi- 39 β Figure 1. (a) Molecular structure of cinnamaldehyde and HP-β-CD gated in which HP- -CD showed higher inclusion complex- (note: HP-γ-CD has a similar chemical structure with eight ation ability with cinnamaldehyde and higher solubility glucopyranose units), and illustration of cinnamaldehyde/CD-IC enhancement for cinnamaldehyde when it was compared 39 formation, (b) electrospinning process of NFs from cinnamaldehyde/ with inclusion complexation of β-CD. Moreover, several CD-IC solution. studies reported the incorporation of cyclodextrin ICs of cinnamaldehyde within the polymeric electrospun NFs for entanglements and overlapping for the fiber formation during antimicrobial wound dressing and antimicrobial active food − 35,40,41 the electrospinning process.14 16 Hence, electrospinning of packaging. For instance, cinnamaldehyde/β-CD-IC- NFs purely from small molecules presents a real challenge. incorporated polylactic acid (PLA) nanofibrous mat was Nevertheless, NFs purely from CD can be electrospun, as CD fabricated as a potential candidate for the use of wound molecules in their highly concentrated solutions can form dressing material due to its antibacterial properties and low 35 substantial aggregates via hydrogen bonding. The presence of cytotoxicity. Also, a polyvinyl alcohol/cinnamon essential such CD aggregates prevents the breakage of the jet during oil/β-CD-IC nanofibrous film was fabricated by electro- electrospinning, and therefore bead-free uniform NFs can be spinning for active food packaging by increasing the high- − electrospun from pure CD.17 19 Furthermore, electrospun NFs temperature stability of cinnamon essential oil by inclusion from a variety of CD-ICs with food flavors and essential oils complexation and prolonging the shelf life of strawberries by 40 such as vanillin,20 vitamin E,21 eugenol,22 menthol,23 thymol,24 showing effective antimicrobial activity. Also, cinnamon and carvacrol25 were also produced successfully. essential oil/β-CD-IC was incorporated into electrospun PLA Cinnamaldehyde (Figure 1a), a primary constituent of NFs for antimicrobial packaging application in which the PLA/ cinnamon bark oil, is an essential oil classified as GRAS cinnamon essential oil/β-CD nanofibrous film has shown (Generally Recognized As Safe) by the U.S. Food and Drug better antimicrobial activity compared to PLA/cinnamon Administration (21 CFR 182.60). Cinnamaldehyde is known essential oil nanofibrous film.41 The improvement of to have high antibacterial, antifungal, anti-inflammatory, and antimicrobial activity was attributed to cyclodextrin inclusion antioxidant activity; therefore, it is widely used in the food, complexation and also, nanofibrous film obtained by the − drug, and cosmetic industries.26 28 For instance, cinnamalde- electrospinning method preserved higher amount of cinnamon hyde-containing films, particles, and NFs have shown the essential oil when compared to film obtained by the casting advantages of use of cinnamaldehyde in various applications method.41 including pharmaceutics, food, and antimicrobial packag- In the light of these aforementioned studies and from our − ing.29 33 For example, Qin et al. showed that active packaging extensive experiences on electrospun polymer-free CD-IC NFs,