In vitro study of the bioavailability of fatty acids in cow milk containing conjugated linoleic acids produced in vivo or added in synthetic form Hajer Jedidi a , Ehab Kheadr a , Fleur Gagnon b , Marie-Rose Van Calsteren b , Edward Farnworth b , Ismail Fliss a, * a STELA Dairy Research Centre, Institute of Nutrition and Functional Foods, Université Laval, Québec, Canada G1V 0A6 b Agriculture and Agri-Food Canada, Food Research and Development Centre, Saint-Hyacinthe, Québec, Canada J2S 8E3 article info Article history: Received 10 October 2013 Received in revised form 13 January 2014 Accepted 15 January 2014 abstract The intestinal absorption of fatty acids from milk, especially conjugated linoleic acids (CLA), was eval- uated using an in vitro simulator. Milk was enriched with c9,t11 CLA by feeding a cow a diet containing 4% safflower oil or by emulsifying synthetic CLA in the form of free fatty acid or triacylglycerol, then standardized to 1.0% or 3.25% fat. Fatty acid bioavailability depended on chain length, presence of double bonds, and the percentage of fat. Absorption was more efficient in the presence of 1.0% fat. The bioavailability of c9,t11 CLA at 3.25% fat was 89% in the milk from the cow fed the safflower-oil diet, and 85% and 71% in milk enriched with synthetic free CLA and synthetic CLA in the form of triacylglycerol, respectively. At 1.0% fat, these values were 90%, 99% and 96%, respectively, suggesting that bioavailability of CLA in milk is affected by the percentage of fat present. Ó 2014 Published by Elsevier Ltd. 1. Introduction Conjugated linoleic acids (CLA) are a group of positional and geometric isomers of unbranched C 18 diene fatty acids. They are receiving increasing attention because of the biological properties that have been attributed to them in recent years: inhibition of carcinogenesis in rats, decreased body fat in mice, reduced atherosclerotic plaque formation in rabbits and hamsters, preven- tion and treatment of diabetes type 2 (Ip et al., 1996; Riserus, Vessby, Arner, & Zethelius, 2004). The principal dietary sources of CLA are animal products. They can be formed by industrial partial hydrogenation or by bio-hydrogenation of linoleic and linolenic acids in the rumen (Griinari et al., 2000). It has been established that cis-9, trans-11 CLA (c9,t11 CLA), the major isomer found in meat and dairy products, is formed as an intermediate during the bio- hydrogenation of linoleic acid to stearic acid in the rumen. It is absorbed from the digestive tract and then into the mammary gland (Dale, Benjamin, & Daniel, 2003). Absorption of fatty acids (FAs) depends on their chain length and number of unsaturated bonds (Ramírez, Amate, & Gil, 2001), and on their regio-specific distribution in the triacylglycerol (TAG) molecule (Bracco, 1994). Several researchers (Chardigny et al., 2003; Fernie et al., 2004; Martin et al., 2000; Terpstra et al., 2003) have studied the intestinal absorption of synthetic CLA supplements in the form of free fatty acid, triacylglycerol or fatty acid ethyl ester. Basically, a number of methods have been used to estimate absorption of different fatty acids including use of isoto- pically labeled substrates (Emken, Adlof, Duval, Nelson, & Benito, 2002) or another fatty acid fed with it as control (Lawson & Hughes, 1988). Besides, digestive lipid metabolism could be stud- ied in vivo through analysis of gastric and intestinal compartments or by sampling through the use of naso-gastric and duodenal tubes (Carrière et al., 2000) or by imaging measurements (Marciani et al., 2007). More recently, the bioavailability of c9,t11 CLA in milk (enriched with synthetic free fatty acid or triacylglycerol or by feeding cows a diet that increases circulating CLA) has been studied in vitro using the TIM-1 (TNO Nutrition and Food Research Insti- tute, Zeist, The Netherlands), a simulator of the human gastro- intestinal tract (Gervais et al., 2009). The TIM-1 is an in vitro model that reproduces different first steps of digestion and ab- sorption of substances in human gastro-intestinal tract. The aim of the present study is to evaluate the impact of fat content and the presence of CLA on the bioavailability of fatty acids in milk, using the TIM-1 in vitro model of human digestion, to evaluate the impact of varying milk fat content (1 and 3.25%) on FAs bioavailability, and to compare the effect of three types of milk * Corresponding author. Tel.: þ1 418 656 2131x6825. E-mail address: ismail.fliss@fsaa.ulaval.ca (I. Fliss). Contents lists available at ScienceDirect International Dairy Journal journal homepage: www.elsevier.com/locate/idairyj 0958-6946/$ e see front matter Ó 2014 Published by Elsevier Ltd. http://dx.doi.org/10.1016/j.idairyj.2014.01.009 International Dairy Journal 36 (2014) 95e100