Starch from the sea: The green macroalga Ulva ohnoi as a potential source for sustainable starch production in the marine biorefinery

The growing population, decreasing arable land and fresh water supply questions the sustainability of terrestrial agriculture for securing safe nutrients supply, particularly starch- an essential ingredient for all staple foods. Here, we report the isolation, characterization and offshore production assessment of native starch from green seaweed Ulva ohnoi cultivated in seawater. Starch content varied from 1.59% to 21.44% depending on growth conditions and seasons. Our results show that nutrient starvation significantly increased the starch concentration up to 21.4% on dry weight basis. The extracted fraction contained 75.45% starch, and the starch extraction yield from the U. ohnoi biomass was 50.37%. Ulva starch granules are spherical, ovoid and irregularly shaped, 5–7 μm in size. Their gelatinization temperature is 69^°C and they are susceptible to α-amylase and amyloglucosidase digestion. U. ohnoi biomass cultivated offshore for 13 months showed an average starch yield of 3.43 ton/ha/year (t·ha⁻¹y⁻¹). This study encourages the potential use of offshore produced biomass for sustainable starch supply as an alternative to current agricultural products, the production of which requires arable land and fresh water.