Competitive displacement of oil body surface proteins by Tween 80 e Effect on physical stability Constantinos V. Nikiforidis, Vassilios Kiosseoglou * Laboratory of Food Chemistry and Technology, Department of Chemistry, Aristotle University of Thessaloniki, GR-54124, Thessaloniki, Greece article info Article history: Received 15 June 2010 Accepted 1 October 2010 Keywords: Oil body Emulsion Maize Tween Stability abstract A concentrated oil body cream, prepared from maize germ by aqueous extraction, was dispersed in water to obtain a natural 5% o/w emulsion. To improve the emulsion physical stability, the hydrophilic surfactant Tween 80 (polyoxyethylene sorbitan monooleate) was incorporated at levels ranging from 0.25 to 2%, and the increase of the oil body mean diameter and the volume of serum separated from the emulsion system, was followed with storage time. In addition, the amount and composition of oil body surface proteins competitively displaced by the surfactant was studied. The improvement in oil body stability against coalescence and creaming, resulting from Tween addition, is discussed in terms of the development at the oil body surface of an adsorbed film of a mixed nature, made up of surfactant- and phospholipid-rich domains, with the non-displaced surfactant protein molecules, mainly oleosins, remaining embedded in the latter. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction In maize germ, as well as in many oil-rich seeds, the lipids are encountered in the form of small-sized organelles called oil bodies (Tzen, Lie, & Huang, 1992). One common feature of all oil bodies, irrespective of their origin, is the presence at their surface of a mixed phospholipidseprotein membrane, responsible for main- taining oil body integrity. In electron micrographs the oil bodies appear to be surrounded by an electron-dense layer, attributed to a single layer of phospholipids, with the acyl moieties directed towards the oil body core (Frandsen, Mundy, & Tzen, 2001). Depending on plant origin, the phospholipids content may range between about 0.6 and 2%. In maize germ oil bodies, the phos- pholipids content is about 0.9%, with phosphatidyl choline and phosphatidyl serine constituting, respectively, 64.1 and 20.2% of the phospholipids fraction (Chen, Chyan, Lee, Huang, & Tzen, 2004; Tzen, Cao, Laurent, Ratnayake, & Huang, 1993). The dominant proteins of the oil body surface are called oleosins (Chen, Lin, Huang, & Tzen, 1997; Jolivet et al., 2004; Simkin et al., 2006; Tzen & Huang, 1992). These are proteins of relatively low- molecular mass (15e20 kDa) with a triblock structure, comprising two amphiphilic N- and C-terminal regions and a central hydro- phobic region of about 70 residues. According to the predicted model of Tzen and his co workers (Huang, 1992), the central hydrophobic oleosin domain, formed by two antiparallel strands, connected by a “proline knot”, is inserted into the triglycerides core and forms a hairpin-like structure while the C- and N-terminal moieties reside on the oil body surface where they interact with the phospholipids. Caleosins are another group of oil body surface proteins. Compared to oleosins, caleosins are minor proteins with a molecular mass close to 27 kDa and a molecular structure comprising a fairly hydrophilic N-terminal moiety, a C-terminal hydrophilic region and a central hydrophobic region inserted, as in the case of oleosins, in the triglyceride core (Lin, Liao, Yang, & Tzen, 2005; Purkrtova, Jolivet, Miquel, & Chardot, 2008; Purkrtova et al., 2008). Steroleosins are the third group of oil body surface proteins. They are also minor proteins with a molecular mass close to 40 kDa that anchor to the oil body surface through their hydrophobic N-terminal domain (Lin, Tai, Peng, & Tzen, 2002; Lin & Tzen, 2004). Oil recovery from oil-rich plant materials is performed indus- trially using organic solvents, such as hexane or petroleum ether. The extracted crude oil is then refined and consumed as bulk vegetable oil or used in the preparation of products appearing in the form of oil-in-water emulsions. A novel idea, recently put forward by a number of investigators, involves extraction of oil in the form of oil bodies by employing aqueous media in place of organic solvents (Chen et al., 1997; Kapchie, Wei, Hauck, & Murphy, 2008; Nikiforidis & Kiosseoglou, 2009, 2010; Towa, Kapchie, Hauck, & Murphy, 2010). This “green technology” approach may lead to the development of a concentrated oil-in-water emulsion made up of small-sized oil droplets protected by a natural mixed proteine phospholipids layer which could be used in the preparation of food * Corresponding author. Tel.: þ30 231 0 997834; fax: þ30 231 0 997779. E-mail address: kiosse@chem.auth.gr (V. Kiosseoglou). Contents lists available at ScienceDirect Food Hydrocolloids journal homepage: www.elsevier.com/locate/foodhyd 0268-005X/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodhyd.2010.10.002 Food Hydrocolloids 25 (2011) 1063e1068