A comparison of protocols for isolating and concentrating protein from the green seaweed Ulva ohnoi

We compared protocols to isolate and concentrate protein from the green seaweed Ulva ohnoi. We quantified the effect of three factors on protein and essential amino acid yields and concentrations in protein isolates and residuals in a factorial experimental design. The three factors were starting material (as dry and milled or fresh and pulped), aqueous solvent-to-biomass ratio (20:1 or 5:1 v/w) and the incubation time in the aqueous solvent (incubated for 16 h at 30 °C or incubated for <1 min at ambient temperature). The protein isolation protocols increased the concentration of protein, total essential amino acids, methionine and lysine ~3 to 5- fold compared to whole U. ohnoi and were considerably more effective than the different protein concentrating combinations, which only increased protein and amino ac- id concentrations by 30–40 % in the residual biomass. The use of fresh and pulped biomass as the starting material, an incubation time of <1 min at ambient temperature and a low aqueous solution volume resulted in the highest pro- tein isolate yield of 22 % of the protein found in seaweed. This study demonstrated that proteins from U. ohnoi were most effectively isolated by adopting protocols for terres- trial leaves compared to the protocols employed for seed crops as traditionally applied to seaweeds.