Interaction of chitosan-based dietary supplements with fats during lipid digestion

Abstract

A commercially-available weight loss supplement and its main ingredient, chitosan, were studied to develop mechanistic insight into their mode of action through the in vitro digestion of lipids and the self-assembly of digestion products. A pH-stat coupled to small angle X-ray scattering (SAXS) was used to monitor both the kinetics of lipolysis and structural behaviour during the in vitro digestion of full cream milk (as a model meal) in the presence of chitosan or the commercial supplement. SAXS was further utilized to probe the equilibrium structures formed between chitosan and oleic acid (the primary digestion product anticipated to interact with the test materials) under varying pH conditions. The extent of digestion and characteristic phase transitions that occur during the in vitro digestion of full cream milk were altered when the supplement was added to the digestion at the manufacturer's recommended dose. Chitosan present in the supplement was able to interact with emulsified oleic acid to form a lamellar liquid crystalline phase, while refined chitosan dissolved in aqueous acetic acid did not produce this structure. It was also demonstrated that at lower pH, self-assembled structures were lost due to the electrostatic driving force for interaction with the chitosan being removed. It was therefore hypothesised that chitosan had the ability to reduce weight gain by electrostatically binding to ionised fatty acids released during digestion in the intestine. The study provides direct scattering-based evidence of the interaction of chitosan with lipid digestion products under intestinal conditions.