Crustaceans and mollusks are widely consumed around the world due to their delicacy and nutritious value. During the processing, only 30-40 % of these shellfish are considered edible, while 70-60 % of portions are thrown away as waste or byproduct. These byproducts harbor valuable constituents, notably chitin. This chitin can be extracted from shellfish byproducts through chemical, microbial, enzymatic, and green technologies. However, chitin is insoluble in water and most of the organic solvents, hampering its wide application. Hence, chitin is de-acetylated into chitosan, which possesses various functional applications. Recently, nanotechnology has proven to improve the surface area and numerous functional properties of metals and molecules. Further, the nanotechnology principle can be extended to nanochitosan formation. Therefore, this review article centers on crustaceans and mollusks byproduct utilization for chitosan, its nano-formation, and their food industry applications. The extensive discussion has been focused on nanochitosan formation, characterization, and active site modification. Lastly, nanochitosan applications in various food industries, including biodegradable food packaging, fat replacer, bioactive compound carrier, and antimicrobial agent have been reported.

The global population is rising sharply and is expected to be 10 billion by 2050. Nutrition security, especially protein, is a major concern, as it is one of the essential ingredients for body growth. However, consumption of meat is unsustainable, as the use of natural resources and greenhouse gas (GHG) emissions are relatively high compared to plant-based protein sources. Aquatic plants like duckweed, Azolla, and water spinach, as well as macroalgae and microalgae, contain good amounts of protein, ranging from 25% to 60% dry weight (DW) and comprising major essential amino acids (EAAs). These plants are rich in vitamins and minerals and possess antimicrobial, anti-inflammatory, antidiabetic, and anti-fatigue properties. In addition, green food processing (GFP) technologies minimize the antinutritional factors, which in turn increase the bioaccessibility and biodigestibility of aquatic plants. Fermentation is one of the oldest known GFP methods. Recent advances include high-pressure processing, pulsed electric field, ultrasound-assisted, and microwave-assisted extraction, which are among the most promising techniques. Hence, government initiatives, as well as research and private sector collaboration for cultivation, processing, and advocating for such nutrient-dense food, are necessary. This will ensure sustainable production and consumption.