## 1 Introduction  
Sea cucumbers are the marine invertebrates of the _Holothuroidea_ class, distributed worldwide and living on the surface of the ocean in warm shallow waters, near corals, seaweeds, or rocks [1; 2; 3]. Approximately 1500 varieties of sea cucumbers are reported to be found worldwide; however, about 100 species are used for food/ medicinal purposes [2]. Sea cucumbers contain more than 50 types of biomolecules, including proteins (amino acids, collagen, and peptides), lipids (polyunsaturated fatty acids), sulphated polysaccharides (fucosylated chondroitin sulphate and fucoidan), ash, lectins, saponins, glycosides, phenolics (phenolic acids and flavonoids), and sterols, which are well reported for their anti-cancer, anti-tumour, anti-coagulation, antioxidant, antidiabetic, antihypertensive, antiglycation, and anti-osteoclastogenesis properties [1; 4; 5; 6; 7; 8; 9]. For instance, sea cucumber processing discards, mainly internal organs along with or without tentacles/aquapharyngeal bulbs/flowers, are rich sources of essential amino acids, polyunsaturated fatty acids, and phenolic compounds, which exhibit potent antioxidant activity [4; 6; 10]. Not only the chemical composition but also the processing of sea cucumbers varies depending on the country of origin, species, and available technologies. For example, Malaysia, the Philippines, China, Madagascar, and some areas of the Pacific use different techniques for sea cucumber processing. However, sea cucumber processing generally includes four stages, namely weeding, boiling, salting, and drying, as shown in Figure 1[9; 11; 12; 13], which possess a positive impact on the product quality [14]. For instance, textural damages, including the denaturation, degradation, and aggregation of proteins, can take place during the processing and storage of sea cucumbers [15]. Their visualization, such as appearance, texture, odour, fungal infection, and proximate composition, including protein, ash, and water contents, are the major parameters to determine the quality of sea cucumbers [9]. The traditional processing reported in Figure 1 with boiling and sun drying often leads to reducing the overall quality of sea cucumbers [12; 14], thereby affecting their selling price both locally and internationally [16]. In addition, different species of sea cucumbers require different processing techniques to gain quality products, including the shape of sea cucumbers. The overall quality mainly depends on the thickness and texture of the body wall (a major marketable body part) of sea cucumbers, along with the water-holding capacity after boiling [11]. For example, the body wall and skin of _Bolandshia vitiensis_ (0.7 cm), _B. similis_ (0.4 cm), _Holothuria edulis_ (0.3 cm), and _Actinopyga milliaris_ (0.9 cm) are soft [17; 18; 19; 20]. Therefore, boiling should be avoided as it can damage the body wall (e.g., hampering the body wall composition), and, hence, salting is required before drying to remove water and inactive microorganisms from the body wall [21]. However, in the case of sea cucumbers such as _Thelenota ananas_ and _Stichopus vastus_, with thick and tough body walls, repeated boiling and drying are needed, which are enough to render the microorganisms inactive; therefore, salting is not required before boiling [21]. On the other hand, the outer skin layer of _Holothuria scabra_ must be removed before boiling because the skin is thick, tough, and chalky [21]. Figure 1: Flow diagram of sea cucumber processing: traditional vs. modern. After harvesting sea cucumbers, hydrolysis starts within a few hours, and due to this, storage and transportation become complex because of quality degradation [22]. Hence, pre-cooking procedures are used in fresh or raw sea cucumbers as they help to prevent auto-enzymatic reactions [22]. After that, pre-cooked sea cucumbers are frozen for storage and kept for further processing [22]. Pre-treatments such as boiling, salting, smoking, drying, or freezing sea cucumbers are essential to produce good-quality products [23].