Chitosan taurocholate capacity to bind lipids and to undergo enzymatic hydrolysis: An in vitro model

Upon mixing a solution of sodium taurocholate with a solution of chitosan acetate, both at pH values close to 4, immediate precipitation of chitosan taurocholate salt is observed. The salt obtained with nearly stoichiometric amounts of both reagents was characterized by infrared spectrometry, and found to exhibit new bands indicative of its ionic nature. Similar compounds were obtained from Na taurodeoxycholate and Na glycocholate. When exposed to a number of hydrolases at pH values close to neutrality and 20 and 37 °C they were found to be poorly susceptible to enzymatic degradation: only Trichoderma reesei cellulase, egg white lysozyme and barley malt α-amylase were effective on chitosan taurocholate and glycocholate. The observed capacities of the freeze-dried salts for olive oil were 22 g oil/g of chitosan taurocholate, 60 g oil/g of chitosan glycocholate, and 27 g oil/g of chitosan taurodeoxycholate. The capacities were 22.1 g butter oil/g of chitosan taurocholate and 22.1 g of corn oil/g chitosan taurocholate. These data, substantially much higher than similar data published for plain chitosan and various oils, mean that the lipid uptake mainly takes place by hydrophobic interactions with the insoluble salts formed by chitosan upon contact with bile. The profile of fatty acids and some components of the unsaponifiable (cholesterol, α-tocopherol and γ-tocopherol) were not different in treated and untreated lipids. A model for the action of chitosan in vivo is discussed.