Unlocking the potential of sea lettuce (Ulva fenestrata) for food applications through tailored stabilisation
Doktorsavhandling, 2026
Seaweed has been identified as a promising alternative food raw material to support the growing demand for sustainable and nutritious food products. The green species Ulva fenestrata is particularly promising based on its sensorial properties and nutritional value. However, rapid post-harvest deterioration limits its full potential for food use, calling for new stabilisation methods beyond conventional drying and freezing.
This thesis investigated how five different stabilisation strategies: osmotic dehydration driven by brining, microbial fermentation, high pressure processing (HPP), sous vide processing (SP) and antioxidant-aided drying, affect the microbial shelf life, colour, texture, volatile compounds, nutritional value and sensory profile of U. fenestrata, with the ultimate aim of diversifying the formats by which it can be used in food.
Concentrated brines containing 25% salt or 50% sugar reduced water activity from 0.98 to 0.80 or 0.89, respectively, and extended microbial shelf life from 13 to 48 or 78 days, respectively. HPP (600 MPa, 3min) outperformed SP (80 °C, 7 min) in terms of initial microbial inactivation, and gave ≥28 days shelf life. Fermentation with selected lactic acid bacteria (LAB) strains (Levilactobacillus brevis, Lactiplantibacillus plantarum and Lactiplantibacillus paraplantarum) increased in vitro-assessed protein digestibility and mineral accessibility. Among the wet-stabilization methods, colour and texture were best kept by concentrated salt brines and SP. However, following prolonged storage in concentrated brines, up to 70% proteins and 42% total fatty acids were lost, indicating a trade-off between microbial spoilage and nutrient retention. Drying at 60 °C better preserved colour than 40 °C, and combining the former with antioxidant rinsing was superior in maintaining seaweed-odour and limiting volatile compound development over 550 days of storage.
Overall, these findings demonstrated that all the evaluated stabilisation strategies, except for SP, can extend the shelf life of U. fenestrata by ≥28 days, but with different effects on sensorial and nutritional properties. The evaluated strategies, which were either new to seaweed as a whole (combined antioxidant treatment and drying, sugar-brining), new to U. fenestrata (salt-brining and LAB-fermentation) or having new settings (SP, HPP), increase the possibilities for high-quality seaweed to reach the food market, and diversify its available formats.
This thesis investigated how five different stabilisation strategies: osmotic dehydration driven by brining, microbial fermentation, high pressure processing (HPP), sous vide processing (SP) and antioxidant-aided drying, affect the microbial shelf life, colour, texture, volatile compounds, nutritional value and sensory profile of U. fenestrata, with the ultimate aim of diversifying the formats by which it can be used in food.
Concentrated brines containing 25% salt or 50% sugar reduced water activity from 0.98 to 0.80 or 0.89, respectively, and extended microbial shelf life from 13 to 48 or 78 days, respectively. HPP (600 MPa, 3min) outperformed SP (80 °C, 7 min) in terms of initial microbial inactivation, and gave ≥28 days shelf life. Fermentation with selected lactic acid bacteria (LAB) strains (Levilactobacillus brevis, Lactiplantibacillus plantarum and Lactiplantibacillus paraplantarum) increased in vitro-assessed protein digestibility and mineral accessibility. Among the wet-stabilization methods, colour and texture were best kept by concentrated salt brines and SP. However, following prolonged storage in concentrated brines, up to 70% proteins and 42% total fatty acids were lost, indicating a trade-off between microbial spoilage and nutrient retention. Drying at 60 °C better preserved colour than 40 °C, and combining the former with antioxidant rinsing was superior in maintaining seaweed-odour and limiting volatile compound development over 550 days of storage.
Overall, these findings demonstrated that all the evaluated stabilisation strategies, except for SP, can extend the shelf life of U. fenestrata by ≥28 days, but with different effects on sensorial and nutritional properties. The evaluated strategies, which were either new to seaweed as a whole (combined antioxidant treatment and drying, sugar-brining), new to U. fenestrata (salt-brining and LAB-fermentation) or having new settings (SP, HPP), increase the possibilities for high-quality seaweed to reach the food market, and diversify its available formats.
volatiles
texture
high pressure
Macroalgae
sous vide
sensory
oven-drying
nutrient digestibility
colour
fermentation
Hall VIVA, floor 10, Chemistry Building, Kemigården 4, Chalmers Campus Johanneberg, Gothenburg.
Opponent: Denise Skonberg, Professor of Food Science, University of Maine
Författare
Mar Vall-Llosera Juanola
Chalmers, Life sciences, Livsmedelsvetenskap
Brining as an effective method to stabilise sea lettuce (Ulva fenestrata) -impact on colour, texture, chemical characteristics and microbial dynamics
Algal Research,;Vol. 83(2024)
Artikel i vetenskaplig tidskrift
Vall-llosera, M., Strand, R., Mazurkewich, S., Algnimi, M., Kinnby, A., Trigo, J., Larsbrink, J., Undeland, I. Sous-vide and high-pressure processing for shelf-life extension of two edible seaweeds: effects on microbial load, colour, texture and enzymatic activity
Unravelling the fermentation potential of Ulva fenestrata by lactic acid bacteria and its impact on protein digestibility and mineral accessibility
Food Research International,;Vol. 245(2026)
Artikel i vetenskaplig tidskrift
Changes in volatiles and sensory profiles during storage of dried Ulva fenestrata: Effects of pre-rinsing and drying temperatures in a large-scale setting
Journal of Food Composition and Analysis,;Vol. 159(2026)
Artikel i vetenskaplig tidskrift
Seaweed could diversify our diets without competing for farmland or freshwater, but is highly perishable and usually spoils rapidly after the harvest. This thesis explored ways to preserve sea lettuce (Ulva fenestrata), a green seaweed from the Swedish coast rich in protein, iron and vitamin B12.
To help U. fenestrata reach our plates, salt and sugar brining, high-pressure processing (HPP), sous-vide, fermentation and drying were investigated for their effects on microbial shelf-life, colour, texture, flavour and nutritional value.
Brining in 25% salt best preserved green colour and texture while preventing microbial growth, extending the shelf life from 13 to 78 days, versus 48 days with 50% sugar. However, brining reduced protein and fatty acid content. HPP had a shelf life of least 28 days but caused browning and softening; sous-vide at 80 °C provided a shelf life of 8 days. Fermentation with selected lactic acid bacteria improved protein digestibility and made iodine and iron more accessible for potential intestinal absorption in a simulated digestion model. Dried U. fenestrata remained stable for up to 180 days before smell and colour changed and compounds linked to lipid oxidation increased. Drying at 60 °C preserved green colour better than at 40 °C. An antioxidant rinse before drying at 60 °C preserved green colour and seaweed smell during storage and reduced formation of volatile compounds for up to 550 days.
This work shows how stabilisation methods can be tailored to the preferred seaweed format -wet biomass, dried flakes or powder- and to the most important properties for its final use; e.g., colour, flavour or nutritional value. The results could help both the seaweed industry to manage large, perishable harvests and the food industry to develop new seaweed-containing products, altogether supporting food preparedness and more varied diets.
To help U. fenestrata reach our plates, salt and sugar brining, high-pressure processing (HPP), sous-vide, fermentation and drying were investigated for their effects on microbial shelf-life, colour, texture, flavour and nutritional value.
Brining in 25% salt best preserved green colour and texture while preventing microbial growth, extending the shelf life from 13 to 78 days, versus 48 days with 50% sugar. However, brining reduced protein and fatty acid content. HPP had a shelf life of least 28 days but caused browning and softening; sous-vide at 80 °C provided a shelf life of 8 days. Fermentation with selected lactic acid bacteria improved protein digestibility and made iodine and iron more accessible for potential intestinal absorption in a simulated digestion model. Dried U. fenestrata remained stable for up to 180 days before smell and colour changed and compounds linked to lipid oxidation increased. Drying at 60 °C preserved green colour better than at 40 °C. An antioxidant rinse before drying at 60 °C preserved green colour and seaweed smell during storage and reduced formation of volatile compounds for up to 550 days.
This work shows how stabilisation methods can be tailored to the preferred seaweed format -wet biomass, dried flakes or powder- and to the most important properties for its final use; e.g., colour, flavour or nutritional value. The results could help both the seaweed industry to manage large, perishable harvests and the food industry to develop new seaweed-containing products, altogether supporting food preparedness and more varied diets.
Blå mat - centrum för framtidens sjömat, del II
Formas (2024-01023), 2025-01-01 -- 2028-12-31.
BLÅ MAT -centrum för framtidens sjömat
Västra Götalandsregionen, 2021-01-01 -- 2024-12-31.
Formas (2020-02834), 2021-01-01 -- 2024-12-31.
Blå åkrar för en grön framtid -tång som en källa till hållbara livsmedel (BlueGreen)
Formas (2021-02340), 2022-01-01 -- 2026-12-31.
Ämneskategorier (SSIF 2025)
Livsmedelsvetenskap
Styrkeområden
Livsvetenskaper och teknik (2010-2018)
DOI
10.63959/chalmers.dt/5952
ISBN
978-91-8103-495-0
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5952
Utgivare
Chalmers
Hall VIVA, floor 10, Chemistry Building, Kemigården 4, Chalmers Campus Johanneberg, Gothenburg.
Opponent: Denise Skonberg, Professor of Food Science, University of Maine