Louise Juul1,5, Lene Stødkilde2,5, Søren K. Jensen2,5, Signe Hjerrild Nissen1,5, Annette Bruhn3,5, Morten Ambye-Jensen4,5, Trine Kastrup Dalsgaard1,5,6
1 Department of Food Science, Aarhus University, Agro Food Park 48, 8200 Aarhus N, Denmark
2 Department of Animal Science, Aarhus University, Blichers Allé 20, 8830 Tjele, Denmark
3 Department of Ecoscience, Aarhus University, CF Møllers Alle 3, 8000 Aarhus C, Denmark
4 Department of Biological and Chemical Engineering, Hangøvej 2, 8000 Aarhus C, Denmark
5 Centre for Circular Bioeconomy (CBIO), Aarhus University, Denmark
6 Centre for Innovative Food Research CiFood, Agro Food Park 48, 8200 Aarhus N, Denmark
Sea lettuce (Ulva spp.) is gaining interest as a potential protein source. However, knowledge on the nutritional quality, especially protein digestibility and bioavailability, is limited. This study is the first to test the in vivo N digestibility in a monogastric animal model. In July 2020, Ulva was harvested from Skive fjord (Denmark) and protein was extracted in a pilot-scale facility. The protein was extracted by double screw pressing and the protein was acid-precipitated from the resulting juice. The N digestibility of the crude biomass and of the extracted protein fraction was tested in rats. The extraction of protein increased the N digestibility with app. 20%, however, the N digestibility was still poor (55.5±2.7%). This was possibly due to a high ash content in the protein extract. Hence, further improvement was needed for an acceptable N digestibility. Therefore, in August 2021, the harvest was repeated, and the processing was optimized by including a biomass rinse step prior to screw pressing and a decanting step of the juice after pressing to reduce the amount of sediment/ash in the final protein extract. This resulted in a protein extract (dried) with a crude protein content of 41.2% and an ash content of 24.2%, whereas the protein extract from 2020 had a crude protein and ash content of 28.1% and 38.8%, respectively. It is hypothesized that the increased protein concentration in the 2021 protein extract will further improve the N digestibility of the Ulva protein, which is tested in a rat trial in November 2022.