Modification of coconut residue fiber and its bile salt adsorption mechanism: Action mode of insoluble dietary fibers probed by microrheology

Abstract

The effect of dietary fiber on lowering blood cholesterol level depends on its ability to separate bile salt (BS) and prevent its recycling. The effects of composition and microstructure of coconut residue fiber (CRF) by modifying on BS retention and adsorption process were studied, and the adsorption mechanism of BS by insoluble dietary fiber (IDF) was investigated. We proved for the first time that adding 0.38 wt% of chitosan to assist in CRF self-assembly could improve effectively IDF's ability to retain multiple BS molecules. The adsorption of CRF to BS was a combination of two modes: rapid adsorption at the initial stage and slow adsorption after the initial stage. The fast adsorption mode plays a dominant role during the early stage of adsorption and is correlated with the viscosity and soluble diary fiber (SDF) content in dietary fiber (DF). In contrast, the slow adsorption mode occurs during the whole adsorption process while plays a dominant role during the middle and late adsorption stages. This mode is also correlated with the non-covalent transient network formed by DF in the system. The formation of a non-covalent transient network is a dynamic process in which the formation and collapse of the system occurs alternately; and this formation relies on the content of free H-bonds in IDF. This study can be helpful for the understanding of the BS-adsorption mechanism of ordinary diary fiber.