Undaria pinnatifida is an unwanted seaweed species in New Zealand that heavily infests local mussel farms. Fucoidan, a sulfated polysaccharide extracted from U. pinnatifida, is known to have greater number of bioactivities. As a dietary supplement, fucoidan is mainly consumed orally. As fucoidan were regarded as indigestible carbohydrates, the enzymatic digestibility in human body has not been studied. It is also important to investigate the digestibility of fucoidan to help understand how fucoidan exerts its health benefits.

The objective of this study was to investigate the enzyme digestibility of fucoidan extracted from the New Zealand U. pinnatifida in human body by using an in vitro digestion model.

In order to determine the digestibility, fucoidan was digested in the in vitro digestion model with 5-min oral, 2h-gastric and 2h-intestinal phases, respectively. The dissolved undigested sample and the fucoidan digesta were fractionated by filters with different molecular weights (100, 10-100, 3-10 and 3 kDa). After the separation, samples were freeze dried and weighed. The weighed sample was then hydrolyzed with Trifluoroacetic acid (TFA) and derivatized with 1-phenyl-3-methyl-5- pyrazolone (PMP). The monosaccharide contents were detected by LC-MS afterwards.

My results suggest that the fucoidan extracted from New Zealand U. pinnatifida can be partly digested in in vitro. The weight and the neutral sugar contents (fucose, galactose, mannose, xylose, rhamnose, glucose and glucuronic acid) of > 100 kDa was decreased significantly after the digestion process. While in small fractions (10-100 kDa, 3-10 kDa and < 3kDa), both weight and neutral sugar contents were significantly increased. Approximately 4 % (w/w of dry weight (dw) fucoidan) and 14 % (w/w) of sugar were detected in 10-100 kDa and 3-10 kDa fractions, respectively after the simulated digestion. The results indicated that the > 100 kDa fraction were cleaved by salivary and intestinal amylases and the gastric juice. Fucoidan was partly digested.

Structural analysis, bioactivities and interactions with the gut microbiota of the partly digested fucoidan can be investigated in the further.