Chemical compositions and nutritional profiles of two edible tunicate species (Halocynthia roretzi and Halocynthia aurantium)

As an abundant marine bioresource, tunicates could be exploited in the food industry. However, limited knowledge of their chemical composition and nutritional profiles prohibited further application. In this study, two common edible tunicate species, Halocynthia roretzi (HR) and Halocynthia aurantium (HA), were subjected to comprehensive composition analysis in terms of moisture, protein, lipids, cellulose, ash, amino acids, fatty acids, non-cellulose carbohydrates and minerals. Reddish HR was much bigger than purple HA with respect to body length and weight, and their moisture fell within 82.98 %-90.92 %. The non-edible outer shell part (OS) and edible internal organs part (IO) had a dry weight ratio of around 3:2 for both two species. Generally, for both HR and HA, IO was more abundant in protein and lipids. In contrast, OS had much higher cellulose contents, confirming the better suitability of IO as a nutritional seafood. IO was richer in essential amino acids and unsaturated fatty acids, while OS had more abundant saturated fatty acids. The detected non-cellulose monosugars ranged from 0.47 % to 1.18 % and indicated the presence of some sulfated glycans. IO of HR had higher contents of essential minerals, such as Cu, Zn, and Fe, while IO of HA showed a higher K content. To sum up, this study identified the chemical composition and nutritional profile variations among different tunicate species and various dissected parts, guiding the development of specific strategies to exploit tunicates for proper food applications.