## 5 Animal Nutrition
### Chemical Methods  
One such chemical method involves the use of specific enzymatic degradation to disrupt the cell walls and facilitate the release of nutrients, such as proteins. Strategies to address the cell wall barrier have been explored in the context of other algal and plant-based sources. A study on _Nile tilapia_ showed that the addition of exogenous enzymes and probiotics to the diet can alleviate the negative effects of plant-derived ingredients, such as increased levels of non-starch polysaccharides and phytates, on nutrient digestibility and gut health [121]. Further research is needed to identify the specific enzymes that can target and break down the antinutritional factors present in duckweed, thereby improving its nutritional profile and suitability for use in animal feed and other applications [128; 129]. [PERSON] et al., (2023) determined the effects of NSP multi-enzymes (containing xylanase, beta-glucanase, cellulase, and mananase) on the growth and feed digestion efficiency of fish fed with duckweed-based feed [130]. Feeding was carried out under four different conditions: feed without enzymes and without duckweed (T0), feed without duckweed but with added enzymes (T1), feed without enzymes but with 5% duckweed (T2), and feed with enzymes and 5% duckweed (T3). The results showed that T3 had the best feeding effect, with an absolute weight gain of 0.91 g, absolute length increase of 0.63 cm, and specific growth rate of 1.35%, compared to a specific growth rate of 0.41%, a survival rate of 100%, and a feed digestion rate of 28.59% for the control group. To the best of our knowledge, enzymatic hydrolysis of duckweed proteins has only been performed three times on duckweed protein powder. [PERSON] et al. (2021) performed enzymatic hydrolyses of proteins from defatted _Lenna minor_ using Flavourzyme and al- catalase to evaluate the antioxidant properties of the hydrolysates [131]. [PERSON] et al. (2022) used alcalase to hydrolyse duckweed (_Wolfia globosa_) proteins and investigated the antimicrobial and functional properties of the fractions obtained [132]. [PERSON] et al. (2024) conducted the first investigation on enzymatic hydrolysis (by popsin, chymotrypsin, papain, and trypsin) of duckweed proteins to produce bioactive peptides with therapeutic applications [133]. They found antihypertensive peptides that inhibit angiotensin-converting enzyme (ACE), effectively reducing blood pressure levels. ACE plays a significant role in the regulation of blood pressure, converting angiotensin I into the potent vasoconstritor angiotensin II while also breaking down the vasodilitor bradykinin, leading to an elevation in blood pressure [134; 135]. In case of proteins, the selection of appropriate extraction buffers and the optimisation of parameters, such as pH and temperature, can play a crucial role in ensuring the efficient extraction and preservation of the duckweed proteome [16; 130]. The degree of protein hydrolysis can be increased with an additional step of chemical extraction of the proteins to produce a protein isolate on which enzymatic hydrolysis can be performed. This step allows the proteins to be concentrated up to higher percentage (~80%) in the product and removes unwanted compounds, such as insoluble proteins and fibres, but several compounds with valorisation potential can also be lost [133]. The most commonly used treatment, fermentation, might also help to decrease the antinutritional factors and crude fibre content, thereby increasing the nutritional value and potential for incorporation into animal and human diets [136]. The fermentation process, carried out by microorganisms or their secreted enzymes, breaks down proteins into smaller peptides and amino acids, thereby increasing the digestibility and bioavailability of protein. Furthermore, fermentation can effectively reduce antinutritional factors in plant-based materials, such as tannins and plytic acid, thus reducing restrictions on the digestion and absorption of protein [124].