Encapsulation of ethylene gas into a-cyclodextrin and characterisation of the inclusion complexes Binh T. Ho, Daryl C. Joyce, Bhesh R. Bhandari ⇑ School of Agriculture and Food Sciences, The University of Queensland, QLD 4072, Australia article info Article history: Received 1 September 2010 Received in revised form 4 November 2010 Accepted 12 January 2011 Available online 18 January 2011 Keywords: a-Cyclodextrins Encapsulation Ethylene gas Inclusion complexes abstract Molecular encapsulation of various apolar compounds with a-cyclodextrin (a-CD) is becoming a widely applied technique to produce food, pharmaceutical and agricultural materials. Encapsulated ethylene in the form of inclusion complexes (ICs) with cyclodextrin, which is in powder form, could be used in fruit ripening and other aspect of plant growth regulation. In this research, ethylene was complexed with an a-CD under 0.2–1.5 MPa for 12–120 h. Ethylene concentration in the inclusion complexes (ICs) varied from 0.98 to 1.03 mol ethylene/mole CD. Pressure and time did not increase ethylene concentrations in the complexes, but did yield significantly higher amounts of the crystal complex. The physico-chemical properties of the ethylene-a-CD complexes at various concentration of ethylene were characterised using X-ray diffractometry (XRD), nuclear magnetic resonance spectroscopy (CP–MAS 13 C NMR), differential scanning calorimetry (DSC), thermogravimetry analysis (TGA), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). Complex formation was confirmed by sharp peaks in the XRD diffractograms, crystal images by SEM, double bond of ethylene gas and chemical shifts at C 4 ,C 3 and C 5 in NMR spectra, intensity changes of C–H bending and C@C stretching in the FTIR spectra, and water loss and physico-chemical property modifications in the DSC and TGA scans. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Encapsulation techniques and encapsulated materials play a significant role in pharmaceutical and food processing industries. Encapsulation techniques involve a substance (guest or core) being entrapped into another material or system (host or carrier). The applied methods aim at improving stability, controlled delivery and convenient handling of active ingredients (Augustin, Sang- uansri, Margetts, & Young, 2001; Desai & Park, 2005). The major encapsulation practices are macroencapsulation (also called coat- ing), microencapsulation, nanoencapsulation and molecular encap- sulation. In molecular encapsulation, cyclodextrins (CDs) are probably the most well-known carrier with their recognised capac- ity to form inclusion complexes (ICs) with apolar guests. Production and structure description of CDs have been discov- ered for century (Singh, Sharma, & Banerjee, 2002). The most com- mon CDs are a-, b- and c-CD, comprising six, seven and eight glucose units, respectively (Cravotto, Binello, Baranelli, Carraro, & Trotta, 2006). Complexation between the guest and the cyclodex- trin molecule takes place once hydrophobic groups of the guest interact with the inner cavity surface of the CD. The binding forces are usually van der Waals, hydrophobic interactions and dipole–di- pole interactions. As a versatile substance, CDs have been increasingly employed in food technology, pharmacy, biotechnology, polymeric nanopar- ticles and other applications (Dodziuk, 2006; Hashimoto, 1996; Yoshii, 2004). Cyclodextrins have been used as encapsulating agents for various purposes such as stabilisation of aroma, docosa- hexaenoic acid (DHA) and vitamins (Bhandari, D’Arcy, & Padukka, 1999; Goubet et al., 2001; Hashimoto, 2006), taste modification (Szejtli & Szente, 2005) and cholesterol removal (Smith, Awad, Bennink, & Gill, 1995). The CDs have particular encapsulation potential with gases. Various gases such as CH 4 ,C 2 H 6 ,C 3 H 8 , Kr, and Cl 2 have been encap- sulated into CDs (Cramer & Henglein, 1956; Hagan, 1962; Rudke- vich & Leontiev, 2004). Other gases also encapsulated into CDs include Xenon (Xe) (Dubois, Parrès, Huber, Berthault, & Desvaux, 2004), 1-methylcyclopropene (1-MCP) (Daly & Kourelis, 2001) and CO 2 (Neoh, Yoshii, & Furuta, 2006). a-CD is the smallest dimension CD (470–530 pm in diameter), and can complex more easily than b- and c-CD with guest molecules having five carbons or less (Hedges, Shieh, & Sikorski, 1995). Ethylene gas, with its apo- lar characteristic and small structure size (C@C and C–H lengths of 132 and 108.2 pm, respectively (Lide, 2009)), is also suitable for inclusion complexation with a-CD. Ethylene is a well-known olefin with the simple structure of two carbons symmetrically linked to each other by a double bond 0308-8146/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodchem.2011.01.043 ⇑ Corresponding author. Tel.: +61 7 33469192; fax: +61 7 33651177. E-mail address: b.bhandari@uq.edu.au (B.R. Bhandari). Food Chemistry 127 (2011) 572–580 Contents lists available at ScienceDirect Food Chemistry journal homepage: www.elsevier.com/locate/foodchem