Unravelling the fermentation potential of Ulva fenestrata by lactic acid bacteria and its impact on protein digestibility and mineral accessibility

Journal article, 2026

Fermentation of Ulva fenestrata by isolated lactic acid bacteria (LAB) can be advantageous due to their adaptability to diverse substrates (e.g., ulvan), and high salinity compared to commercial strains. This study aimed at identifying LAB strains holding promise for both fermentation and enhanced nutrient digestibility of U. fenestrata focusing on proteins and microelements. Fifty LAB strains were selected for evaluation, of which thirty-six were revived and screened using water extracts from U. fenestrata. From the initial 36 LAB strains, 30 were able to reduce the pH to <4.5 within 24 h in Ulva substrate. Six strains were further screened with whole Ulva biomass, resulting in four being able to reach pH <4.5 within 48 h and presenting proteolytic activity, with Lactiplantibacillus plantarum NFICC19 being superior in both, followed by Levilactobacillus brevis NFICC1668 and Lactiplantibacillus paraplantarum NFICC1922. These three strains were then used for larger-scale fermentations, in which carbohydrate profiles indicated a relative reduction in glucose for all strains. After in vitro digestion according to INFOGEST protocol, the degree of protein hydrolysis (DH) of U. fenestrata fermented with L. brevis NFICC1668 presented a significantly higher value, 71%, compared to the fresh biomass or the unfermented control having DH of 29% and 42%, respectively. In addition, L. paraplantarum NFICC1922 gave the highest iodine (32% vs 18% in the control) and iron accessibility (38% vs 11% in the fresh biomass). Overall fermentation with L. brevis NFICC1668, can increase protein digestibility and iodine accessibility, whereas L. paraplantarum NFICC1922 can improve iodine and iron accessibility.