###### Abstract  
Sea cucumbers from unharvested areas, are underutilized resources which may have the potential to become a future food resource. The aim of this study was to evaluate protein quality and investigate the changes in antioxidant activity from frozen and freeze-dried red sea cucumber (_Parastichopus tremulus_) subjected to digestion, using an in vitro digestion model. _P. tremulus_ constituted high moisture content (90%), comparable protein (4%) and ash (4%) content, and low lipid (1%) content. The biochemical components in freeze-dried samples were largely retained during the freeze-drying process. Frozen samples showed significantly higher (_p_ < 0.05) antioxidant activity compared to freeze-dried samples (calculated on a dry weight basis). The quantity of essential amino acids was high (31%) and corresponds to the Food and Agriculture Organization of the United Nations reference protein. Frozen samples showed an increase in antioxidant activity during digestion measured by three different antioxidant assays. Freeze-dried samples only showed an increase in one of the antioxidant assays. Correlations (_p_ < 0.05) were found between specific free amino acids and antioxidant activity. The amount of free amino acids exceeded the threshold to taste bitter, umami, sour, and sweet flavors. This study showed that _P. tremulus_ constitutes good protein quality, performed antioxidant activity, and has the potential to be used as a flavor-enhancing ingredient.  
sea cucumber; protein quality; amino acids; in vitro digestion; antioxidant activity; umami flavor; seafood; marine organisms +
Footnote †: journal:  
This includes _Holothuria whitmaei_ from the Great Barrier Reef in Australia [9] and _Thelenotaanas_[10].  
Sea cucumbers contain valuable vitamins and minerals (zinc, iron, magnesium, and calcium) [11; 12]. Furthermore, sea cucumber has been reported to constitute important essential amino acids (EAAs) which could contribute to the nutritional value [11]. Sea cucumber may also have the potential to contribute to the umami flavor in foods [13].  
The Norwegian red sea cucumber (_Parastichopus tremulus_) is distributed from the Barents Sea in the north to the Canaries in the south [14; 15]. _P. tremulus_ has gained attention in the Asia market due to its red color [6]. _P. tremulus_ are mainly exported to Asian markets as frozen or dried products [16].  
During normal metabolism, reactive oxygen species (ROS) are constantly produced, having an adverse effect on the human body, initiating accelerated cell death, and causing tissue damage when not countered [17]. Antioxidants perform an essential role in counteracting these ROS, preventing diseases, and maintaining human health [18]. Sea cucumbers have previously been shown to contain several bioactive compounds, including amino acids and peptides, which express antioxidative and anti-inflammatory properties [1; 12]. This suggests that consumption of sea cucumber could attenuate the ROS formation in the human body [17]. The availability of bioactive peptides in sea cucumbers could be increased through enzymatic hydrolysis [13; 19] or released naturally during gastrointestinal digestion [20].  
The aim of this study was to evaluate protein quality and investigate the changes in antioxidant activity from frozen and freeze-dried red sea cucumber (_Parastichopus tremulus_) subjected to digestion, using an in vitro digestion model.