## 5 Animal Nutrition
The bioaccessibility of a compound, which refers to the amount that is released from the food matrix and available for absorption, is often more relevant than its mere content within the plant. The bioavailability of bioactive compounds is influenced by their chemical structure, interactions with other components during digestion, and the properties of the food matrix [114; 114]. For example, the presence of secondary metabolites, such as polysaccharides and organic acids, can interfere with the solubility and separation of proteins during SDS-PAGE [16]. Duckweed, like many other plant-based foods, can have a complex matrix that may hinder the release and absorption of beneficial compounds [96; 116]. For example, factors such as crude fibre content and ash levels influence the digestibility outcomes [117]. Species like _Lemma minor_ and _Lemma gibba_ typically show higher digestibility compared to _Spirodela polyrhiza_, which in comparison has higher fibre content. Lignin content is an important component of plant cell walls, and if its content is too high, it can make the cell walls more difficult to break down, which is not conducive to the digestion and absorption of nutrients. Additionally, lignin can form complexes with proteins, which resist breakdown in the stomach environment, thereby reducing the solubility and digestibility of proteins [118]. Research has shown that the lignin content in duckweed is extremely low, which has a minimal impact on the absorption and utilisation of proteins [119]. However, the unique cell wall structure is primarily composed of cellulose embedded in a matrix of other polysaccharides, which can pose challenges in accessing the plant's bioactive compounds and ensuring adequate digestibility. This is naturally recalcitrant to the deconstruction carried out by microbes and enzymes [52]. Duckweeds, being a rapidly growing and highly efficient phytoremediator, can potentially accumulate various contaminants and toxins from the environment, which can lead to the presence of antinutrients. Antinutrients are substances present in plants that can interfere with the absorption or utilisation of nutrients by the human or animal body [24; 71]. The presence of other potential antinutritional factors in duckweed can also affect the absorption of nutrients, such as oxalates, phytates, and tannins, which are common in plant-based foods [120]. Soluble oxalates can form insoluble crystals with Ca\({}_{2+}\) and Mg\({}_{2+}\), leading to reduced absorption and utilisation of calcium in the body, and they can easily induce hypocalaemia and kidney metabolism disorders [121]. About 70% of phosphorus (P) in plants exists in the form of phytate-P, which is difficult to digest and absorb in monogastric animals (such as pigs and chickens) and in humans without sufficient phytase. Therefore, high levels of phytates can lead to lower biological phosphorus utilisation [122]. High concentrations of tannins in food can inhibit the digestion and utilisation of nutrients such as proteins, carbohydrates, vitamins, and minerals by binding with them to form indigestible substances, suppressing digestive enzymes and gastrointestinal bacteria [123]. [PERSON] et al. (2022) conducted an analysis of the contents of oxalates, phytates, and tannins in duckweed, finding that their levels in duckweed are relatively low, with minimal impact on the digestion and utilisation of nutrients [50]. Another potential antinutrient in duckweeds is phytic acid, which can chelate essential minerals such as iron, zinc, and calcium, reducing their absorption [87]. Another challenge arises from the variations in bioactive compounds' contents and distribution within duckweed. Factors such as the source/species, growth conditions, and processing methods can significantly impact the concentration and bioavailability of these compounds [14]. _In vivo_ studies have been conducted to assess and mitigate these antinutrient factors.