## 3 Duckweed as an Alternative Source of Nutrients and Bioactive Compounds
### Carbohydrates  
In duckweed, the cell wall contains several carbohydrate components that contribute to its structure and function, but their presence and roles can vary slightly depending on the species and environmental conditions. Duckweed, being a small aquatic plant, has relatively simple and thin primary cell walls that primarily consist of cellulose, hemicellulose, and pectin. Lignin, a complex phenolic polymer typically found in vascular plants for strengthening secondary cell walls (e.g., in wood and xylem tissues), is minimal (negligible) or absent in duckweed due to its aquatic lifestyle and lack of extensive vascular structures. Cellulose is a primary and essential component of the cell wall in duckweed. It forms microfibrils that provide structural support and tensile strength. Hemicellulose is a secondary structural component in the cell wall. It crosslinks with cellulose microfibrils, contributing to the wall's flexibility [52]. Pectin is abundant in the primary cell wall of duckweed, especially in younger or growing tissues. It forms a gel-like matrix that helps maintain cell wall porosity and adhesion between cells, as well as playing a role in water retention [53]. Pectin is known to undergo changes in response to biotic or abiotic stresses, and these changes can have significant implications for plant development, immunity, and industrial applications, such as biomass conversion for biofuel production [54]. Duckweed's fibre content, which can reach up to 45% of its dry weight, makes it a potentially valuable source of this important nutrient [24; 55]. Duckweed's fibre content, which includes both soluble and insoluble forms, may offer additional advantages. The high dietary fibre content in duckweed helps maintain gut health, promotes normal digestive function, and contributes to controlling blood sugar levels. Soluble dietary fibres (in water and from gels), such as pectin and hemicelluloses, are known to have beneficial effects on human health, including the regulation of blood sugar levels and helping to slow down the absorption of fats (weight management), which may be beneficial for individuals with conditions like diabetes or high cholesterol [56]. Furthermore, they help in the promotion of a healthy gut microbiome [13]. These soluble fibres are highly digestible and can be readily absorbed by the human body. On the other hand, insoluble dietary fibres, such as cellulose and lignin, are less readily digestible but play an important role in maintaining a healthy digestive system (reducing the risk of digestive issues) by adding bulk to the stool and promoting regular bowel movements. Additionally, more in-depth studies are required to elucidate the potential health benefits and applications of the soluble and insoluble dietary fibres found in these versatile aquatic plants [13; 24; 26; 42]. From a technological perspective, the incorporation of duckweed fibres in food products presents several advantages. The incorporation of duckweed fibres in food products could contribute to the development of novel functional and textural properties. Duckweed fibres could potentially be used as natural thickeners, emulsifiers, or stabilisers, potentially enhancing the mouthfeel and overall quality of food products. The high energy content of duckweed, primarily in the form of easily fermentable starch, makes it a promising feedstock for biofuel production, further enhancing its value as a sustainable resource [57]. Starch, however, is primarily a storage carbohydrate, not embedded in the cell wall matrix. Instead, starch is stored in plastids (e.g., chloroplasts) within the cell cytoplasm and can accumulate significantly under certain specific stress conditions, such as nutrient deficiency (limited nitrogen or phosphorus availability) or salinity stress [26]. In fact, starch accounts for about 4.0% to 29.8% of duckweed [36], but duckweed grown under specific conditions can contain up to 40% starch by dry weight, highlighting its potential as a renewable energy source [42].