Study of interactions between aroma compounds and acacia gum using headspace measurements Géraldine Savary * , Nicolas Hucher, Odile Petibon, Michel Grisel Université du Havre, URCOM, EA 3221, FR CNRS 3038, 25, rue Philippe Lebon CS 80540, 76058 Le Havre cedex, France article info Article history: Received 19 July 2013 Accepted 28 October 2013 Keywords: Arabic gum Flavour release PRV method Retention Hydrophobic interactions Concentration effect abstract This study deals with retention measurements of aroma compounds in acacia gum aqueous solutions. In that purpose, six volatile molecules differing in their physicochemical properties were analysed: ethyl butyrate, ethyl hexanoate, ethyl octanoate, cumene, 1-octanol and linalool. Their gas/liquid partition coefficients were measured by headspace gas chromatography using the phase ratio variation method from acacia gum solutions. Three acacia gum samples exhibiting different emulsifying properties were studied for concentrations ranging from 0 to 20 wt%. These measurements made possible to evaluate the interactions between aroma compounds and acacia gums through the calculation of retention. A cor- relation between retention and lipophilicity was observed, thus proving that acacia gum interacts with aroma compounds via hydrophobic bonding. Significant interactions occur for volatile molecules that have a pronounced lipophilic character (logP > 3.6). The effect of gum concentration was also studied. No linear relationship was evidenced with retention and a significant effect was observed for concentration higher than 5 wt%. This work also establishes that the emulsifying properties of acacia gum can be evaluated by retention measurements for lipophilic aroma compounds (logP > 3.6). Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction The flavouring process of food, and especially beverage, remains a difficult task due to the complex and reversible association of its two main components, an aqueous matrix and some lipophilic volatile molecules. To improve the stability of such mixtures, spe- cific additives are usually used in order to enhance the stability and to ease the formulation steps (Dickinson, 2009). Acacia gum (GA) is among the most used additive for beverage flavouring as it is an effective emulsifier used to stabilize aroma compounds in the aqueous phase (Given, 2009). Acacia gum, an exudate from Acacia trees growing in African sub-desert areas, is usually described as a complex heteropolysaccharide containing about 2% of proteins. Three major molecular species have been isolated for the polymer backbone: arabinogalactan (AG), arabi- nogalactan protein (AGP), and glycoprotein (GP) (Randall, Phillips, & Williams, 1989; Renard, Lavenant-Gourgeon, Ralet, & Sanchez, 2006). This structural complexity makes difficult the comprehen- sion of mechanisms leading to the stabilization of complex food products. In particular, few studies focused on the investigation of the mechanisms of interaction between acacia gum samples and flavour compounds. Some authors suggested hydrophobic in- teractions (Savary, Hucher, Bernadi, Grisel, & Malhiac, 2010; Terta, Blekas, & Paraskevopoulou, 2006) but neither the nature of bind- ing nor the conditions of formation were clearly established. Therefore, it is notably important to evaluate the critical hydro- phobicity value (logP) for an aroma compound, necessary for the occurrence of interactions with acacia gum. Moreover, as most natural products, acacia gum is subject to chemical variability that will affect its functional properties and therefore it is crucial to find an easy way to evaluate the emulsi- fying ability of each gum sample. Gel permeation chromatography is currently used to characterize acacia gums, especially the amount of the most surface-active AGP fraction (Al-Assaf & Phillips, 2006) but remains a quite complex technique sometimes unable to discriminate one GA sample to another in spite of significant dif- ferences in their emulsifying ability. In a previous paper we were able to show that, in some cases, these abilities could be predicted on the basis of the association properties of GA solutions and aroma compounds (Savary et al., 2010). Nevertheless these assertions relied on two volatile molecules, a-terpineol and ethyl decanoate, and it seemed important to confirm that only the knowledge of physicochemical properties of the chosen molecules was required to predict the emulsifying ability of random acacia gum samples. In this study, we evaluate several volatile molecules, chosen among aroma compounds, through the study of their retention in * Corresponding author. Tel.: þ33 232 744399; fax: þ33 232 744391. E-mail address: geraldine.savary@univ-lehavre.fr (G. Savary). Contents lists available at ScienceDirect Food Hydrocolloids journal homepage: www.elsevier.com/locate/foodhyd 0268-005X/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.foodhyd.2013.10.026 Food Hydrocolloids 37 (2014) 1e6