A clarification of concepts related to the digestion and absorption of carotenoids and a new standardized carotenoids bioavailability evaluation system

The published literature has shown that there are various evaluation methods for the process of carotenoids digestion and absorption. However, it was found that many concepts are ambiguous in the evaluation process, and the selection of evaluation methods is inappropriate and inaccurate. These deficiencies trouble readers, hamper comparisons among different studies, and generate controversy in different literature. Therefore, it is imperative to establish a complete and standardized system for evaluating the digestion and absorption process of carotenoids. This review begins by clarifying confusing concepts during the process of carotenoids digestion and absorption, including the release rate, micellization rate, bioaccessibility, relative bioavailability and absolute bioavailability. Then this review discusses relevant factors affecting the key process of the digestion and absorption of carotenoids. Finally, a more specific and standardized system for evaluating carotenoids bioavailability was suggested based on four dimensions: intake, digestion, absorption and metabolic process. Clarifying concepts such as digestion and absorption and standardizing corresponding research methods will help to obtain reliable data and support interoperability and comparisons across studies.