Physicochemical and release characterisation of garlic oil-β-cyclodextrin inclusion complexes

Abstract

Garlic oil (GO), rich in organosulphur compounds, has a variety of antimicrobial and antioxidant activities, however, its volatility and low physicochemical stability limit its application as food functional ingredients. The aim of this study was to investigate the physicochemical and release characterisation of inclusion complexes of GO in β-cyclodextrin (β-CD). The formation of GO/β-CD inclusion complex was demonstrated by different analytical techniques including Fourier transform-infrared spectroscopy, differential scanning calorimetry and X-ray diffractometry. The stoichiometry of the complex was 1:1. The calculated apparent stability constant of GO/β-CD complex was 1141 M⁻¹, and the water solubility of GO was significantly improved by the phase solubility study. Furthermore, the release of GO from the inclusion complex was determined at a temperature range from 25 to 50 °C and in an acidic dissolution medium (pH 1.5), respectively. The release rate of GO from the inclusion complex was controlled.

Introduction

Garlic (Allium sativum L.) is a widely distributed plant and is used throughout the world not only as a spice and a food, but also as a folk-medicine, and many of the beneficial health-related biological effects have been attributed to its characteristic organosulphur compounds (Rybak, Calvey, & Harnly, 2004). Steam distillation is widely used to extract and condense the volatile organosulphur compounds in garlic, and the final oily product is called garlic oil (GO) (Wu et al., 2002). The compounds of GO mainly are diallyl disulphide (DADS), diallyl trisulphide (DATS), allyl propyl disulphide, a small quantity of disulphide and probably diallyl polysulphide (Pranoto, Salokhe, & Rakshit, 2005). GO is recognised to be more potent than aqueous extracts of garlic and exhibit a wide range of pharmacological properties including antimicrobial, antidiabetic, antimutagenic, and anticarcinogenic effects (Agarwal, 1996). However, the application of GO in the food industry is limited due to its volatility, strong odour, insolubility in water, and low physicochemical stability (Corzo-Martínez, Corzo, & Villamiel, 2007). Interestingly, theses disadvantages can be addressed by complexation with cyclodextrins (CDs) in aqueous solutions. It has been reported that the inclusion complexes of guest compounds with CDs can enhance guest stability, improve the aqueous solubility, protect against oxidation, light-induced decomposition, and heat-induced changes, and mask or reduce unwanted physiological effects, and reduce volatility (Hedges, 1998). For example, the natamycin/CDs complexes have allowed a homogeneous delivery system of natamycin to the shredded cheese surface without the clogging of spray nozzles during cheese production (Koontz & Marcy, 2003).

CDs are non-toxic macrocyclic oligosaccharides, consisting of (α-1,4)-linked α-d-glucopyranose units, with a hydrophilic outer surface and hollow hydrophobic interior (Szente & Szejtli, 2004). CDs are widely used in the food industry as food additives, for stabilization of flavours, for elimination of undesired tastes or other undesired compounds such as cholesterol and to avoid microbiological contaminations and browning reactions (Astray, Gonzalea-Barreiro, Mejuto, Riao-Otero, & Simal-Gándara, 2009). They have the ability to form inclusion complexes with a wide variety of organic compounds, which enter partly or entirely into the relatively hydrophobic cavity of CDs simultaneously expelling the few high-energy water molecules from inside (Karathanos, Mourtzinos, Yannakopoulou, & Andrikopoulos, 2007). The most common CDs used as formulation vehicles are α-, β- and γ-CDs containing six, seven and eight glucopyranose units, respectively. Amongst the CDs, β-CD is widely used since its cavity size is suitable for common guests with molecular weights between 200 and 800 g/mol and also due to its availability and reasonable price (Waleczek, Marques, Hempel, & Schmidt, 2003). Hadaruga, Hadruga, Rivis, Gruia, and Pinzaru (2007) have reported the thermal and oxidative stability of the A. sativum L. bioactive compounds/α and β-CD nanoparticles and discussed that the DADS and DATS were suitably encapsulated in a higher concentration. It has also been reported that the molecular inclusion complexes could be successfully formed by hydrogen bonding between GO and β-CD and an improvement of stability, solubility, and bioavailability of the guest molecule in the inclusion complex was obtained (Ayala-Zavala et al., 2008). Stellenboom, Hunter, Caira, Bourne, and Barbieri (2009) described the preparation of the inclusion complex formed between the allicin mimic S-p-tolyl t-butylthiosulphinate and β-CD by both kneading and co-precipitation methods. Bai et al. (2010) have recently reported that two major GO components of DADS and DATS had higher water solubility caused by hydroxypropyl β-cyclodextrin (HP-β-CD) and DATS was better suited to be encapsulated by HP-β-CD compared to DADS.

However, to the best of our knowledge, there are, so far, few reports on the inclusion complex of GO and β-CD in the scientific literature. In this study, the inclusion complex of GO/β-CD was prepared by the co-precipitation method and the formation of the inclusion complex of GO with β-CD was analysed by different analytical techniques including UV–visible spectroscopy, Fourier transform-infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC) and X-ray diffractometry (XRD). Furthermore, the solubility and release characterisation of the inclusion complexes of GO in β-CD were determined.