Effect of human and simulated gastric juices on the digestion of whey proteins and carboxymethylcellulose-stabilised O/W emulsions Ernesta Malinauskyte ˙ a , Jovita Ramanauskaite ˙ a , Daiva Leskauskaite ˙ a,⇑ , Tove G. Devold b , Reidar B. Schüller b , Gerd E. Vegarud b a Department of Food Science and Technology, Kaunas University of Technology, Radvilenu str. 19, LT-50254 Kaunas, Lithuania b Department of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences, N-1432 Ås, Norway article info Article history: Received 2 February 2014 Received in revised form 21 April 2014 Accepted 14 May 2014 Available online 22 May 2014 Keywords: Emulsions Digestibility Whey proteins Carboxymethylcellulose abstract In this study, we analysed the impact of carboxymethylcellulose (CMC) on lipid digestion and physico- chemical properties of whey proteins (WP)-stabilised emulsions during in vitro digestion with either artificial or human gastrointestinal juices. The emulsions were made by adsorbing WP on the fat droplets and subsequently adding CMC, which does not interact with the adsorbed proteins. The limited hydrolysis of lipids and their higher physical stability was recorded for WP-stabilised emulsions in the presence of CMC under simulated gastrointestinal conditions. The possible mechanism by which CMC lowers the digestion of WP-stabilised emulsions is related to the limited interaction of fat droplets with gastrointestinal fluids due to the extended thickening network formed by CMC in the continuous phase. The digestion of WP- and CMC-stabilised emulsions in the in vitro model with human gastric fluids led to greater lipid hydrolysis, although the enzymatic activity in both in vitro models was observed at the same level. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction Designing food emulsions to control the stability, digestion and release of lipophilic food compounds has been a subject of interest for food researchers in recent years (Li et al., 2010; Scholten, Moschakis, & Biliaderis, 2014). In particular, researchers have focused on developing emulsions with specific structural and physicochemical characteristics. This approach includes combining milk proteins and polysaccharides under appropriate conditions to improve emulsions’ stability and to enhance their resistance to enzymatic degradation with the aim of reducing lipid bioavailabil- ity during and after processing (Singh & Sarkar, 2011). Whey proteins are well known to improve emulsions’ stability by reducing interfacial tension and forming a protective membrane around fat droplets. Polysaccharides can act as emulsion stabilisers by increasing the viscosity or gel strength of the continuous phase, as well as by inducing the flocculation of emulsion droplets through bridging or depletion mechanisms, depending on the adsorbing properties of the polysaccharides (Dickinson, 2009). Different methods of interfacial layer design using proteins and polysaccharides can be found in the literature, such as the layer-by-layer electrostatic deposition method (Gu, Decker, & McClements, 2007) or the covalent cross-linking of a protein- polysaccharide complex based on the Maillard reaction (Evans, Ratcliffe, & Williams, 2013). Because the stability, structure and physicochemical properties of food emulsion can influence the subsequent digestion and absorption of fats, in vitro studies on emulsion digestion has become the subject of many scientific reports (Helgason, Gislason, McClements, Kristbergsson, & Weiss, 2009; Sarkar, Horne, & Singh, 2010; Yao et al., 2013). Depending on the physico- chemical properties of the interfacial layer surrounding the lipid droplets, they may breakup or coalescence as the emulsion passes through the mouth into the stomach and then the intestines, at the same time altering the surface area of lipid exposed to enzymes (Pal, 1996). Another phenomenon contributing to the properties of the interfacial layer is the ability of gastric and pancreatic lipases to adsorb to their surfaces, influencing their different actions upon the lipids contained within the droplets (Sonesson, Elofsson, Brismar, & Callisen, 2006). The investigations show that controlling the interfacial characteristics of the droplets, as well as manipulat- ing the emulsions’ structure and composition, should influence the rate or extent of lipid digestion and absorption (Li & McClements, 2014; Mun, Decker, Park, Weiss, & McClements, 2006). The impact of different biopolymer networks on the digestive breakdown of casein-monoglyceride-stabilised emulsions was investigated by Wooster et al. (2014). It was determined that the rates of lipolysis http://dx.doi.org/10.1016/j.foodchem.2014.05.078 0308-8146/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Tel.: +370 37 456426; fax: +370 37 300152. E-mail address: daiva.leskauskaite@ktu.lt (D. Leskauskaite ˙ ). Food Chemistry 165 (2014) 104–112 Contents lists available at ScienceDirect Food Chemistry journal homepage: www.elsevier.com/locate/foodchem