Characterization of emulsion stabilization properties of quince seed extract as a new source of hydrocolloid Emrah Kirtil, Mecit H. Oztop ⁎ Department of Food Engineering, Middle East Technical University, Ankara 06800, Turkey abstract article info Article history: Received 13 January 2016 Received in revised form 27 March 2016 Accepted 18 April 2016 Available online 20 April 2016 The capability of seed extracts in stabilizing emulsions has particularly received interest in recent years. Upon soaking quince seeds into water, biopolymers inside the seeds are extracted to water, forming mucilage. This study investigates the physical stability, rheology and microstructure of oil (sunflower oil) in water emulsions, stabilized by 2% (w/v) whey protein isolate with varying concentrations of xanthan and quince seed gum. Quince seed gum resulted in emulsions with smaller low-shear viscosities and shear thinning capabilities compared to the same concentrations of xanthan. Quince seed gum emulsions with concentrations ≤ 0.1 (w/v), displayed rapid creaming due to bridging flocculation. Despite the difference in apparent viscosities, for gum concentrations b 0.2 (w/v), both gums demonstrated comparable stability with xanthan gum in general yielding marginally more stable emulsions. Gum concentrations N 0.3 (w/v) resulted in physically stable emulsions even after 5 months. Overall, quince seed gum displayed significant emulsification and stabilization properties. © 2016 Elsevier Ltd. All rights reserved. Keywords: Quince seed gum Xanthan gum Creaming Emulsion stability Oil-in-water (O/W) emulsion 1. Introduction Preparation of a wide range of food products involves the dispersion of oil into water. The dispersion of oil in water increases the contact area, hence the interfacial tension between the two phases and carries the system to a higher overall free energy state. In agreement with the thermodynamic dictum that all systems prefer to be in their minimum energy state, the two phases have a tendency to separate and minimize interfacial area (Damodaran, 2005; McClements, 1999). These thermo- dynamically unstable systems can be kinetically stabilized by minimiz- ing the rate of separation. Some favored methods of accomplishing this are, addition of amphiphilic molecules that adsorb on the interface and decrease interfacial tension, or addition of non-adsorbing thickening polysaccharides that reduce particle movements and collisions in emulsions by increasing the viscosity of the continuous phase (Bouyer, Mekhloufi, Rosilio, Grossiord, & Agnely, 2012). Whey protein isolate (WPI) is a mixture α-lactalbumin and β- lactoglobulin and several other minor proteins (Sun, Gunasekaran, & Richards, 2007) and is widely used as a natural emulsifier in food products (Sun & Gunasekaran, 2009). When dissolved in emulsions, WPI tends to be rapidly adsorbed on the surface of oil droplets in the form of a stabilizing monolayer that prevent droplet agglomeration through a combination of electrostatic and steric interactions (Gwartney, Larick, & Foegeding, 2004). In addition to surfactants, polysaccharides are often added in order to thicken emulsions, thereby decreasing the rate of common destabilization mechanisms such as flocculation, creaming, sedi- mentation or Ostwald ripening (Bouyer et al., 2012). Xanthan gum (XG) is one of the most preferred polysaccharides in this regard. XG is an anionic polysaccharide produced by the bacterium, Xanthomonas campestris. The structure consists of a β-(1–4)-D-glu- cose main chain and side chains of α-D-mannose, β-D-glucuronic acid and β-D-mannose as terminal residues (Bouyer et al., 2012). The polymer, when dissolved in water, exists as multiple forms of helices that are in interaction with one another, forming a complex yet loosely bound network (Jansson, Kenne, & Lindberg, 1975; Melton, Mindt, & Rees, 1976). This particular arrangement gives the gum its unique thickening and shear thinning properties (Benmouffok-Benbelkacem, Caton, Baravian, & Skali-Lami, 2010). Quince is a fruit of the west Asian region, which is commonly culti- vated in Caucasus regions, Syria, Afghanistan, Iran, Dagestan and Antal- ya (Trigueros, Pérez-Alvarez, Viuda-Martos, & Sendra, 2011). The scientific name of ordinary quince is Cydonia oblonga (Abbastabar, Azizi, Adnani, & Abbasi, 2015). A mature fruit contains roughly 10 seeds (Abbastabar et al., 2015). Seeds embody a mucinous material, which could be extracted upon mixing with water. Though the seeds have been used for years in Turkish culinary for gelling, they have recently attracted researchers' attention, which caused an increase in the amount of research on the subject. A number of researchers have demonstrated applications for this new source of hydrocolloid (Abbastabar et al., 2015; Hakala et al., 2014; Jouki et al., 2014a, b; Ritzoulis et al., 2014; Trigueros et al., 2011). Studies revealed that, Food Research International 85 (2016) 84–94 ⁎ Corresponding author. E-mail address: mecit@metu.edu.tr (M.H. Oztop). http://dx.doi.org/10.1016/j.foodres.2016.04.019 0963-9969/© 2016 Elsevier Ltd. All rights reserved. Contents lists available at ScienceDirect Food Research International journal homepage: www.elsevier.com/locate/foodres