Food ingredients from cultivated seaweeds-Improving storage stability and protein recovery
Doctoral thesis, 2019
The protein and lipid content in seaweed is related, e.g. to the nutrient access and physical parameters of the surrounding environment. By applying alterative cultivation, the protein and fatty acid content in U. lactuca were increased 3.4 respective 1.5 times by nitrate addition. Furthermore, the protein content was increased by cultivation at low temperature (12 °C) and light (50 μmol photons m-2 s-1), and the fatty acid content was increased by low light and high temperature (18°C).
The polyunsaturated fatty acids (PUFAs) in seaweed could make the dried biomass susceptible to lipid oxidation, with co-oxidation of pigments and vitamins. However, during long-term storage (≤520 days) of oven- and freeze-dried P. umbilicalis and U. lactuca, there was only a moderate development of the lipid oxidation-derived aldehydes, malondialdehyde, 4-hydroxy-trans-2-hexenal and 4-hydryoxy-trans-2-nonenal, while there was a great loss of unsaturated fatty acids and ascorbic acid. Light stimulated the fatty acid loss as well as bleaching of chlorophyll.
Several advantages are foreseen from concentrating the seaweed proteins. This calls for food grade and scalable fractionation methods. The pH-shift process, using alkaline protein solubilisation followed by isoelectric precipitation, was in this work adapted and improved for P. umbilicalis, U. lactuca and S. latissima, e.g. by including freeze-thawing-stimulated protein precipitation. When then comparing the new pH-shift process to two other fractionation methods, the pH-shift method resulted in extracts with the highest protein content: 71%, 51% and 41% per dry weight for P. umbilicalis, U. lactuca and S. latissima, respectively. The protein contained 37-41% essential amino acids. The highest achieved protein yields using the pH-shift method were 23%, 6% and 25%, respectively, for the listed species. For U. lactuca, the yield was further raised to 29% by incorporating a pre-incubation step at pH 8.5 prior to further protein solubilisation at pH 12. The pH-shift process was also successfully used as a first step in a sequential recovery of proteins, carrageenan, pectin and cellulose from P. umbilicalis, showing potential as a biorefinery tool. Throughout the work, the effect of different protein analysis methods on the achieved concentrations of protein in seaweed and seaweed protein extracts was evaluated. This revealed that the analytical choice has a profound impact on the results, especially for the extracts.
To summarise, it was possible to increase the level of proteins and lipids in seaweed through alterative cultivation protocols, and the seaweed proteins could then be further concentrated using the pH-shift process. These results strengthen the possibility that seaweed biomass can be a valuable complement to terrestrial vegetarian food protein sources. If considering the seaweed PUFAs as an added value to recover along with proteins, caution must, however, be taken when it comes to pre-processing storage of the seaweed biomass; these nutrients easily degrade during storage of dried seaweeds, especially in the presence of light.
unsaturated fatty acids
macroalgae
alterative cultivation
sequential recovery
pH-shift
ascorbic acid
long-term storage
Seaweed
protein extraction
proteins
lipid oxidation
Author
Hanna Harrysson
Chalmers, Biology and Biological Engineering, Food and Nutrition Science
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Production of protein extracts from Swedish red, green, and brown seaweeds, Porphyra umbilicalis Kützing, Ulva lactuca Linnaeus, and Saccharina latissima (Linnaeus) J. V. Lamouroux using three different methods
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A Strategy for the Sequential Recovery of Biomacromolecules from Red Macroalgae Porphyra umbilicalis Kützing
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Strategies for Improving the Protein Yield in pH-Shift Processing of Ulva lactuca Linnaeus: Effects of Ulvan Lyases, pH-Exposure Time, and Temperature
ACS Sustainable Chemistry & Engineering,;Vol. 7(2019)p. 12688-12691
Journal article
Algers näringsinnehåll varierar och beror på mängden lösta näringsämnen i havet samt olika fysiska parametrar. Odlingsförsök med U. lactuca visade att protein- och fettinnehållet ökade när nitrat tillsattes i odlingsvattnet. Proteininnehållet ökade även vid låg temperatur och svagt ljus, medan fettinnehållet ökade vid hög temperatur och svagt ljus.
Det relativt höga innehållet av fleromättade fettsyror kan göra alger känsliga för oxidation, i dagligt tal kallat härskning. Detta kan även initiera nedbrytning av vitaminer och pigment. Under lagring av torkad P. umbilicalis och U. lactuca såg vi dock endast en svag ackumulering av de tre utvalda härskningsprodukterna MDA, HHE och HNE, men en kraftig nedbrytning av fleromättade fettsyror, C-vitamin och pigment, speciellt när algerna lagrades ljust.
Trots det höga proteininnehållet i alger antas spjälkningen i mag-tarmkanalen vara dålig p.g.a. algernas starka cellväggar och höga innehåll av polyfenoler. Därför behövs en skalbar och miljövänlig process för att extrahera ut proteinerna från algerna. Vi fann att pH-skiftprocessen, där proteiner löses ut vid högt pH och sedan fälls ut vid lågt pH, gav proteinextrakt som i torkad form hade 71, 51 och 41% protein vardera från P. umbilicalis, U. lactuca och S. latissima, jämfört med 32, 20 och 10% protein i respektive obehandlad alg. Dessutom koncentrerades fettsyrorna in för både U. lactuca och S. latissima, vilket kan öka värdet på extrakten ytterligare. Generellt sett är proteinutbytet vid extraktion av algproteiner lågt men vår forskning har lett till att utbytet ökat från som lägst 6%, till som mest 29%. pH-skiftprocessen applicerades även som ett inledande steg i en lyckad sekventiell extraktion av protein, karragenan, pektin och cellulosa från P. umbilicalis, vilket visar på möjligheten att utnyttja hela algbiomassan utan att skapa restprodukter.
Resultaten från denna avhandling stärker hypotesen att alger är en lovande framtida proteinkälla. Genom optimerad odling kan det initiala proteininnehållet ökas och därefter koncentreras ytterligare med hjälp av pH-skiftsprocessen. För att parallellt med proteinerna kunna dra nytta av algernas fleromättade fettsyror behöver hänsyn tas till hur algerna behandlas före en eventuell extraktionsprocess, eftersom fettsyrorna lätt bryts ner, speciellt i närvaro av ljus.
Driving Forces
Sustainable development
Subject Categories
Food Engineering
Areas of Advance
Life Science Engineering (2010-2018)
ISBN
978-91-7905-144-0
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4611
Publisher
Chalmers
Sal KA, Kemigården 4, Göteborg
Opponent: Dr. Susan Løvstad Holdt, Technical University of Denmark, Danmark.