## 5 Animal Nutrition
### Physical Methods  
Promising approaches include the use of traditional pretreatment processing methods such as drying, crushing, or pressing to enhance the digestibility and bioavailability of compounds in duckweed. The use of hydrothermal liquefaction, a thermochemical conversion process, has been explored to enhance the extraction of valuable compounds from duckweed biomass [37]. The use of ultrasound-assisted extraction has been shown to facilitate the release of important biomolecules from microalgae, such as _Dunaliella salina_[143]. While these strategies have shown promise in other systems, their applicability and effectiveness in overcoming the cell wall barrier of duckweed remain to be thoroughly investigated. Ultrasound technology has emerged as a promising solution to address these challenges, offering the potential to enhance the digestibility, bioavailability, and bioaccessibility of duckweed-derived compounds. Ultrasound-assisted extraction has been investigated as a sustainable and environmentally friendly approach to extracting proteins and other bioactive compounds from various plant sources, including duckweed [144]. The use of ultrasound can disrupt the plant cell walls, facilitating the release of intracellular compoundsand improving mass transfer, thereby enhancing the extraction yield and functionality of the extracted compounds. The propagation of pressure oscillations in the liquid medium during ultrasound-assisted extraction can result in the formation, growth, and collapse of microbubbles, allowing for cell disruption and improved mass transfer. This could contribute to the more effective utilisation of duckweed as a valuable source of nutrients, pharmaceuticals, and biofuel feedstock [126; 144; 145]. [PERSON] et al. (2024) optimised the alkaline extraction of protein from duckweed (_Lemma minor_) with ultrasound by a Box-Behnken experimental design [146]. In addition, an exploration of the effects of ultrasound on the morphological, structural, and functional properties of the extracted protein was also carried out. They concluded that the cellular disruption produced by ultrasound was beneficial for the extraction of more protein. Furthermore, the application of ultrasound during the extraction of protein generated changes in the colour and structure of the duckweed protein, which resulted in improvements in its properties. These results are promising when considering the utilisation of duckweed in diverse food products. [PERSON] et al. (2024) investigated the effects of duckweed forms (fresh and over-dried), duckweed-to-aqueous solution ratio (DSR), alkaline extraction (AE), ultrasound-assisted alkaline extraction (UAAE), and ultrasound-assisted water extraction (UAWE) on protein yield and, furthermore, the physicochemical and techno-functional properties of duckweed protein extracts (from _Wolfifa arrhiza_) [147]. Duckweed in fresh form resulted in a 2.5-fold higher protein recovery than oven-dried duckweed. UAAE significantly enhanced the extraction yield and protein recovery. The optimal extraction process was a DSR of 1:6 using UAAE at pH 8.5, resulting in a 16% yield and 34% protein recovery. Furthermore, the study found that UAAE facilitated the extraction of non-polar/hydrophobic amino acids, while AE proved to be efficient in extracting sulphur-containing amino acids (in addition to enhancing dietary fibre extraction, which helped stabilise the emulsion). This study, for the first time, revealed the role of UAAE and AE in promoting the extraction of different profiles of amino acids. The duckweed protein extract produced using UAAE contained 65% protein (with an excellent essential amino acid content), meeting the WHO/FAO/UNU recommended protein intake for preschool-aged children. Furthermore, the duckweed protein extract exhibited excellent emulsifying properties and oil-holding capacity comparable to commercial soy protein isolates. Overall, UAAE was identified as a promising approach for producing techno-functional and nutritious protein ingredients from _Wolfifa arrhiza_.