Colon-targeted delivery systems for nutraceuticals: A review of current vehicles, evaluation methods and future prospects

Background: Advances in nutriology have suggested the colon as a superior site for nutrition absorption. Nutraceuticals, including phytochemicals, probiotics, etc., have received great attention owing to their health-promoting functionalities for colon. However, these compounds generally exhibit poor solubility or are sensitive to the harsh environment of food processing and gastrointestinal tract, thus, lowering their bioavailability and compromising their envisioned benefits. Therefore, there is a need to develop suitable delivery systems to protect active agents from these severe conditions and to maintain their functions in the colon. Scope and approaches: Colonic delivery of nutraceuticals has emerged as a new impetus for researchers interested in developing functional foods. This review presents an overview mainly about current studies relevant to different colon-targeted vehicles for nutraceuticals. The physiological conditions of colon and the corresponding principles for constructing vehicles are first reviewed to better understand the mechanisms of different vehicles. Relevant methods for evaluating the efficiency of vehicles are also summarized. Last, current limitations and the future scope for the colonic delivery of nutraceuticals are identified and addressed. Key findings and conclusions: Recently, significant progress has been made in colon-targeted delivery of nutraceuticals and different evaluation methods were applied to assess the efficacy of vehicles. However, advances in the colonic delivery of nutraceuticals are still in their early stages and multi-unit vehicles with great efficacy need to be further investigated. Furthermore, to fully mimic the real conditions of gastrointestinal tract, more systematic and precise in vitro/vivo testing should be explored to make sure that a fully function of nutraceuticals enters the colon.