In-vitro digestion models: a critical review for human and fish and a protocol for in-vitro digestion in fish

Abstract

Digestive systems in human, animals, and fish are biological reactors and membranes to digest food and extract nutrients. Therefore, static and dynamic models of in-vitro digestion systems are developed to study e.g. novel food and feed before in-vivo studies. Such models are well developed for human, but not to the same extent for animals and fish. On the other hand, recent advances in aquaculture nutrition have created several potential fish meal replacements, and the assessment of their nutrient digestibility is critical in the application as a fish meal replacement. Using an in-vitro method, the assessment of an ingredient digestibility could be faster and less expensive compared to using an in-vivo experiment. An in-vitro method has been widely used to assess food nutrient digestibility for humans; however, its application for fish is still in the early stages. Both the human and fish as monogastric vertebrates share similar gastrointestinal systems; thus, the concept from the application for humans could be applied for fish. This review aims to improve the in-vitro digestion protocol for fish by adapting the concept from then study for humans, summarizing the current available in-vitro digestion model developed for human and fish in-vitro digestion study, identifying challenges specifically for fish required to be tackled and suggesting an engineering approach to adapt the human in-vitro gastrointestinal model to fish. Protocols to conduct in-vitro digestion study for fish are then proposed.

Evolution of in vitro digestibility techniques: a systematic review

“…It is worth noting that from the beginning of the 1990s, the pH-stat method has been used only to assess feed ingredients for aquatic animals, which is linked with the simplicity of their digestive tract, in particular, the enzyme composition, as well as with the wide use of sources of easily digestible proteins, such as fish meal, for their feeding [36]. Up to now, all accumulated data obtained by the pH-stat method especially using purified enzymes extracted from the stomach and intestine of the targeted animals have been in agreement with the in vivo digestibility analyses on the targeted aquatic animals [37,38]. In conclusion, it is necessary to note that the average constant of casein dissociation and the number of peptide bonds are used in calculation of the degree of hydrolysis of the objects analyzed as standards to eliminate restrictions of the method [8].…”

In Vitro Digestibility Study: Evaluating Plant Proteins Digestibility in Anabas testudineus and Channa punctata

“…In vitro digestibility trials are important as they provide a pre-absorption estimation of nutrient bioavailability. These trials are best suited for evaluating the variations in the bioaccessibility of nutrients and the effect of different factors on their potential for intestinal absorption [3,13]. The drop in pH in the in vitro digestibility test corresponds to the release of protons due to hydrolysis of the peptide bonds by the protease present in the crude extract [13].…”

“…These trials are best suited for evaluating the variations in the bioaccessibility of nutrients and the effect of different factors on their potential for intestinal absorption [3,13]. The drop in pH in the in vitro digestibility test corresponds to the release of protons due to hydrolysis of the peptide bonds by the protease present in the crude extract [13]. All the tested plants were found to have a lower RPD% compared to casein, which may be attributed to the purity and absence of antinutritional factors in casein.…”

“…However, poor knowledge of digestibility in specific fish species has been a major concern for the utilization of plant proteins in fish feed. Digestibility study is most important for suitable feed formulation [13] because it decides the species' bioavailability of energy and essential nutrients [14]. In vitro digestibility study is an important method as it simulates the digestive process and environment in laboratory conditions.…”

“…This method has been elaborated in many animals [15,16], including aquatic animals like fish and prawns [14]. The in vitro methods are usually quicker and more inexpensive than in vivo methods [13] and speciesspecific [11]. This method is particularly useful for preliminary screening, where large numbers of test samples are to be evaluated for different species [17].…”