Abstract: Porphyra haitanensis is an important food resource containing abundant dietary fiber, protein, active substances and trace elements essential for the human body. P. haitanensis is always be harvested for several times during its life cycle. P. haitanensis at the sixth harvest is known as low-value P. haitanensis due to inferior sensory quality, poor palatability and low commercial value. Here, the main nutritional composition and polysaccharide composition of low-value P. haitanensis were analyzed by chemical methods and spectroscopic methods. Compared with high-yield P. haitanensis at the third harvest, low-value P. haitanensis showed a remarkable increase in the contents of crude protein (35.30%), crude fat (0.51%) and crude fiber (5.11%), a dramatic decrease in the contents of total sugar (34.57%) and polysaccharides (20.67%), a similar ash content (10.37%) and a K/Na ratio of 6.3. Hot-water polysaccharide extract from low-value P. haitanensis consisted of a single component with a 28.54 kD molecular weight, which was mainly constituted by galactose (83.12%), 3,6- anhydrogalactose (15.71%) and sulfate group (10.61%). In summary, the results obtained show that low-value P. haitanensis is a high-protein, high-natural dietary fiber, low-fat, low-calory nourishing healthcare food resource.

Key words: low-value Porphyra haitanensi, nutritional components, polysaccharide