## 3 Major Pre-Treatments for Sea Cucumber Processing
### Boiling/Heating  
Boiling is required to inactivate microorganisms or reduce microbial decomposition to obtain a quality dried product from sea cucumbers [9]. According to the thickness and texture of the body wall of different sea cucumber species, boiling period and temperature vary greatly. Sea cucumber species with a thin body wall (0.7 cm), such as _Bohalschia vitiensis_, require 5 to 10 min of treatment at 50 to 90 \({}^{\circ}\)C. Due to boiling, the texture and appearance of sea cucumbers become elastic and cylindrical [23]. Extreme or very high temperatures should be avoided for boiling because it causes damage to the skin and decreases the appearance of sea cucumbers [48]. Moreover, in industry, sea cucumbers are boiled in hot water to inactivate endogenous enzymes to control proteolysis, including muscle tissue (myofibrillar protein), connective tissue (collagen), and sarcoplasmic protein [24; 49; 50]. Boiling time is correlated to boiling pressure and temperature; therefore, an appropriate boiling time is required to degenerate the muscle tissues to make them soft [29; 48; 51]. Due to the prolonged boiling time, the physical properties of the body wall of sea cucumbers, such as hardness, springiness, chewiness, cohesiveness, and resilience, can be significantly decreased, but adhesiveness could be increased (Table 3). Further, these textural properties are strongly related to a sea cucumber's collagen fibre [52]. A sea cucumber's body wall contains collagen, which is highly thermolabie; therefore, adequate time and temperature should be considered during boiling pre-treatment. Boiling has been reported to dramatically affect the structure and composition of collagen in sea cucumbers [53; 54; 55]. [PERSON] et al. [56] reported that the collagen fibres of sea cucumber body walls are rearranged and gelation happens under the temperature of 100 \({}^{\circ}\)C. Nonetheless, when the temperature exceeds 100 \({}^{\circ}\)C, the chemical bonds within the collagen fibres are broken, and the decomposition of collagen fibres starts and causes texture deterioration [57]. [PERSON] et al. [23] stated that 69.81% of collagen was decreased at 80-90 \({}^{\circ}\)C of boiling in _Holothuria scabra_ (Table 4). Even some physiochemical properties, including water-holding capacity, protein degradation, oxidation, and sensory properties, deteriorate simultaneously with high temperatures over 100 \({}^{\circ}\)C [49]. However, [PERSON] et al. [58] reported that the protein content and cooking yield were increased by 78.5 and 70.3%, respectively, when sea cucumbers were boiled at 100 \({}^{\circ}\)C for 45 min as a pre-treatment over the control. Moreover, Table 4 shows that the body wall of _Apostichopus japonicus_ was boiled at 100 \({}^{\circ}\)C for 10 min, and the saponin content was decreased by 41% over the control [47]. Hence, boiling is traditionally and commercially considered one of the most important pre-treatments for sea cucumber processing. However, boiling at an appropriate temperature and duration should be conducted to maintain physicochemical and nutritional characteristics. Heating is a crucial stage of sea cucumber processing because it deactivates the autolytic enzymes. In the meat industry, the texture of the meat becomes harder, along with the reduction in water-holding capacity, degradation of protein extractability, and protein solubility due to overheating [59]. Therefore, to improve the eating quality of meat, such as maintaining good muscle, texture, and colour, low-temperature heating is required [57]. The textural quality of the sea cucumber body wall is altered under different heat treatments. Collagen fibres are rearranged under 100 \({}^{\circ}\)C, then textural properties deteriorate above 100 \({}^{\circ}\)C due to the lower moisture content. Table 3 shows an enhanced hardness and chewiness under 100 \({}^{\circ}\)C while springiness, resilience, and cohesiveness are increased above 100 \({}^{\circ}\)C [57].