## 3 Results and Discussion
### Free Amino Acids and Ummi Flavor in Frozen and Freeze-Dried Materials
The results are presented as average \(\pm\) standard deviation, \(n=10\). In both frozen and freeze-dried samples, alanine was the most abundant FAAs in the'sweet' group, followed by lysine, threonine, and serine. Regarding bitter flavor, histidine constituted the highest concentration of FAAs in the 'bitter' group, followed by leucine, tyrosine, valine, phenylalanine, isoleucine, and methionine in both frozen and freeze-dried samples. In addition to having a bitter taste, phenylalanine and tyrosine have also been shown to improve the umami flavor [38]. Glutamine has been previously reported to contribute to both sweet and umami flavors [37]. Glycine is related to sweet flavor and arginine is related to bitter flavor [37]. As glycine and arginine could not be separated by the method in this study, and glutamine contributes to two different flavors, they are added to the 'other' flavor group. In addition, freeze-dried samples showed significantly higher (\(p<0.05\)) FAAs concentrations in all flavor groups compared to frozen samples, except aspartic acid in the umami/sour group. A major challenge to transitioning from regular diets to plant-based diets is the lack of umami taste in plant-based foods [42]. Seafoods have therefore been suggested to contribute with the highly sought umami flavor in plant-based diets [42]. Sea urchin [43], snow crab [44], squid [45], oyster [46], and scallop [47] contain high amounts of glutamic acid, which has been shown to increase the umami flavor. A previous study reported high quantities of glutamic acid in the sea cucumber (_Holothuria scabra_) [48]. _P. tremulus_, in this study, contained high levels of glutamine, glutamic acid, and glycine. In addition, other compounds such as salts, sugars, bases, esters, organic acids, and peptides, and the synergy between these compounds may contribute to flavors in foods [37]. However, the components contributing to flavor may vary with processing method, environments, biochemical compositions, and species [38]. Drying by the use of elevated temperature has previously been reported to up-concentrate bitter compounds in raw materials [49]. Freeze-drying on the other hand, is known to be a more gentle process [50], maintaining heat-sensitive biomolecules, and nutrient composition [51; 52] as well as the protein quality in materials such as sea cucum  
Figure 3: Distribution of free amino acids (FAAs) (mg/100 g dry weight sea cucumber (SC)) in frozen and freeze-dried red sea cucumber (_Parastichopus tremulus_). The distribution is grouped with different taste perceptions umami/sour (**a**), sweet (**b**), bitter (**c**), and other (**d**). The frozen samples have theoretically been calculated from wet weight to dry weight. The results are presented as mean \(\pm\) standard error (\(n=10\)). Values with different letters are significantly different (\(p<0.05\)). ber (_Stichopus japonicus_) [53], but at the cost of high energy consumption and long drying times [53]. It has been found that the minimum threshold limit of flavors such as salty, bitter, umami, and sweet were at concentrations of 0.05, 0.08, 0.09, and 0.2 mg/L, respectively [54]. However, the taste perception threshold varies with body mass, sex, and age [55]. In this current study, the concentrations of umami/sour, bitter and sweet flavor found in both frozen and freeze-dried samples exceed the minimum taste perception threshold. Therefore, both frozen and freeze-dried samples may potentially contribute to the umami flavor and can be used as a taste enhancer or employed as a potential food ingredient.