Digestive behaviours of large raw rice particles in vivo and in vitro rat stomach systems

•A novel dynamic in vitro rat stomach (DIVRS) system was presented and studied.•Digestive behaviours of large-size raw rice particles were compared between in vivo and in vitro rat stomach systems.•Better repeatability and similar digestive behaviours were achieved in vitro than that in vivo.•The DIVRS with rather gentle action presented as good digestion capacity as the STR did at the high stirring speed.

In vivo (testing on living animals) and in vitro experiments are the two main approaches to studying the digestive behaviours of different kinds of foods within the gastrointestinal (GI) tract. In our previous work, an initial dynamic in vitro rat stomach (DIVRS) system was created to investigate its digestion capacity of casein powder (water suspension) using an angled plate driven by a motor and an eccentric shaft to create pulsing compression on a polymeric rat stomach model. This indicated that the system was effective in showing the correct trends of the digestion and emptying of solid or semi-solid food matter with small particle size. In this paper, raw rice particles (larger size) were used as model food to study their digestive behaviours with the aid of the same DIVRS and a simple stirred tank reactor (STR). These results were then compared with the in vivo experiments of the living rats. Moreover, the effect of rotating speeds of the impeller in the STR on the digestive behaviours of raw rice particles was also investigated. Better repeatability and similar digestive behaviours were achieved in both the STR and the DIVRS than that could be obtained in the living rats. Both of the STR and DIVRS were effective in reducing the large raw rice particles into small ones. However, the digestive efficiency and buffering ability in vitro were lower than that in vivo due to less sufficient mixing of ingested materials. The stirring speed had a significant influence on the particle digestion in the STR; so, stirring speed must be considered in terms of using STR as an in vitro digestion system for studying digestive behaviours in the GI tract. The mixing behaviour needs to be quantified and understood. Further improvement has to be made by setting up more powerful contractions within the walls on the DIVRS to make it more attractive for practical applications.