Rheological Behavior and Droplet Size Distribution of Emulsions Stabilized by Whey Proteins and Chitosan during ex vivo Digestion

The effect of type of emulsifier, 2 w/w% whey protein concentrate (WPC) or 2 w/w% WPC and 0.1 w/w% chitosan (CH) on the rheological changes and droplet size distribution during the ex vivo digestion of oil in water emulsions (pH 2) containing 1 w/w% rapeseed oil (RSO) were investigated. The procedure was used to mimic the human gastro duodenal digestion in two steps, gastric phase at pH 2 for 30 min followed by the duodenal phase at pH 7 for 60 min. With regard to viscosity, the emulsion, either WPC or WPC-CH showed an increase from gastric phase to duodenal phase (p<0.001) and then it was stable until the end of digestion. The viscosity of WPCCH emulsions during the whole digestion (with/without added HGJ/HDJ) process was higher than the respective WPC emulsions. At pH 7 (duodenal juice addition), the droplet diameters stabilized by WPC emulsion showed a bimodal distribution with droplet sizes in the range of 0.05-1.7 μm and 200-500 μm. A significant change (p<0.01) in the overall droplet size distribution was observed by corresponding WPC-CH emulsion (10-200 μm) at that pH. In comparison, at pH 2 the droplet sizes of initial WPC and WPC-CH emulsions were in the lowest range 0.05-1.0 μm except for a very small peak for WPC emulsion (150700 μm). The increase in droplet sizes during successive digestion from gastric to duodenal phase might be due to flocculation and coalescence. Differences in viscosity and droplet sizes between WPC emulsion and WPC-CH emulsion during digestion may be of importance for the degradation, lipolysis and transit time of the molecules and thereby for their bio accessibility. Our results might indicate a lower digestibility of the emulsion due to the presence of CH in WPC emulsion. INTRODUCTION The design of research on oil in water (o/w) emulsions has gained insights into their physicochemical characteristics and stability behavior under different food processing conditions since last 15 years. Proteins, due to their high surface activity, used to stabilize emulsions, whereas polysaccharides acts as viscosifying agents . The combination of proteins and polysaccharides may provide much better stability to emulsions due to the molecular interactions between them when they carry opposite charges. Whey proteins have high emulsion activity and are used in food industries to stabilize emulsions. Chitosan, a cationic polysaccharide isolated from shrimp waste, is a dietary fibre with good emulsifying properties which depends on the degree of deacetylation and molecular weight. Also, it has water/fat binding capacity. The chitosan coatings improves the stability of protein-coated lipid droplets. Rheological Behavior and Droplet Size Distribution of Emulsions Stabilized by Whey Proteins and Chitosan during ex vivo Digestion Ashoka Sreedhara, Gerd E. Vegarud, Dag Ekeberg, Tove G. Devold, Elling O. Rukke and Reidar Barfod Schüller Department of Chemistry, Biotechnology and Food Science, Norwegian University of Life Sciences, P.O.Box 5003, N-1432 Ås, Norway