pubs.acs.org/JAFC Published on Web 06/03/2009 © 2009 American Chemical Society 5720 J. Agric. Food Chem. 2009, 57, 5720–5726 DOI:10.1021/jf9003412 In Vitro Assessment of the Bioaccessibility of Tocopherol and Fatty Acids from Sunflower Seed Oil Bodies DANIEL A. WHITE, † IAN D. FISK, § SAKUNKHUN MAKKHUN, § AND DAVID A. GRAY* ,§ † Plymouth Marine Laboratory, Prospect Place, The Hoe, Plymouth, England PL1 3DH, and § Division of Food Sciences, School of Biosciences, Sutton Bonington Campus, University of Nottingham, Leicestershire, England LE12 5RD The in vitro digestibility (proteolytic and lipolytic) and bioaccessibility of nutritionally important compounds (R-tocopherol and fatty acids) have been studied for natural sunflower (Helianthus annuus) oil body suspensions in comparison to artificial emulsions emulsified with polyoxyethylene- 20-sorbitan-monolaurate (Tween 20) or whey protein isolate. Proteolytic digestion of emulsions with pepsin (pH 2) promoted significant increases in mean particle size of the whey protein isolate stabilized emulsion (1.8-2.9 μm) and oil bodies (2.3-22.5 μm) but not the Tween 20 stabilized emulsions. SDS-PAGE of proteolytic digestion products suggested degradation of the stabilizing oleosin protein (ca. 18-21 kDa) in oil bodies. The rate of oil body hydrolysis with lipase was significantly slower than the lipase-catalyzed hydrolysis of the artificial emulsions and exhibited a prolonged lag phase. Results from simulated human digestion in vitro suggested that the mean bioaccessibility of R-tocopherol and total fatty acids from oil bodies (0.6 and 8.4%, respectively) was significantly lower than that from the Tween 20 stabilized emulsion (35 and 52%, respectively) and the whey protein isolate stabilized emulsion (17 and 33%, respectively). These in vitro results suggest that oil bodies could provide a natural emulsion in food that is digested at a relatively slow rate, the physiological consequence of which may be increased satiety. KEYWORDS: R-Tocopherol; fatty acid; Helianthus annuus; oil body; emulsion; digestion bioaccessibility INTRODUCTION Plant seeds store cellular triacylglycerol (TAG) in spherical droplets called oil bodies that are utilized as a source of energy during seed germination. These oil bodies (typically 0.5-2.5 μm in diameter) are mainly composed of a TAG core (94-98% w/w) surrounded by a monolayer of phospholipids (0.5-2.0%) em- bedded with small alkaline proteins specific to oil bodies called oleosin (15-26 kDa molecular mass; 0.5-3.5%) and some minor proteins called caleosins and steroleosins (1-5). These proteins provide a thickened surface layer that prevents coalescence of oil bodies in the cytosol of oilseed cells (1, 6) and, together with a net negative charge at neutral pH, prevent coalescence ex vivo when oil bodies are dispersed to form a suspension. Oil bodies isolated from plant seeds into aqueous media are therefore a natural emulsion that may represent a vehicle to deliver natural, minimally processed, pre-emulsified oil into appropriate food systems. Sunflower oil is an accepted dietary source of lipid for human consumption, having a favorable composition of fatty acids from a nutritional perspective, and is also a rich source of R-tocopherol. This oil-soluble vitamin has been widely reported as an important powerful antioxidant in the human diet, which may exert beneficial effects in humans includ- ing protection against cardiovascular disease and cancer (7-9). Oil bodies isolated from sunflower seeds, and indeed other plant species, are enriched in tocochromanols (10, 11) . However, what is not known is the rate of oil body digestion, and associated nutrient release, in the gastrointestinal tract. The bioavailability of micronutrients from food sources is a critical concept in understanding their functionality in human health. In vitro techniques, designed to mimic the human diges- tive system (namely, conditions in the stomach and small intes- tine), have been used to evaluate the digestibility and bioaccessibility of a range of micronutrients, including vitamin E, from fruits and vegetables (12, 13). These techniques are becoming increasingly popular due to the labor intensive, time- consuming, and costly nature of human studies. Moreover, good correlations have been found with carotenoid bioaccessibility data derived from investigations in vitro and in vivo with humans (12 ); in vitro methods are useful as preliminary assessment of bioavailability, but should be followed by in vivo studies. To date, only simple lipolytic assays have been used to assess the action of lipase on natural oil bodies (14-16). Often this has been examined from the perspective of lipase activity in the seed itself, although work by Beisson et al. (16 ) has examined the effect of human pancreatic lipase on the lipolysis of almond oil bodies. Although of undoubted interest, these assays do not take into account the digestive processes that take place in the stomach prior to lipase hydrolysis in the small intestine, for example, the action of proteolytic enzymes at acidic pH. This enzymic action *Corresponding author [telephone 00 44 (0)1159 516147; fax 00 44 (0)1159 516142; e-mail David.Gray@nottingham.ac.uk].