Abstract
Here we evaluated the levels of lipid oxidation products, fatty acids, ascorbic acid and colour of Porphyra and Ulva after oven-drying at 40 °C, and during subsequent storage for ≥370 days under light, semi-light and dark conditions. Part of the seaweed was pre-soaked in freshwater or pre-coated with a whey protein mixture. Controls consisted of freeze-dried seaweeds. Throughout storage there was a moderate development of the lipid oxidation-derived aldehydes, malondialdehyde, 4-hydroxy-trans-2-hexenal and 4-hydroxy-trans-2-nonenal, while there was a great loss of unsaturated fatty acids and ascorbic acid. Light storage and freeze-drying stimulated the fatty acid loss as well as pigment bleaching, seen as increased a*-values. For Ulva, the coating reduced malondialdehyde, 4-hydroxy-trans-2-hexenal and 4-hydroxy-trans-2-nonenal formation during drying and slightly prevented loss of polyunsaturated fatty acids during light storage. Pre-soaking in freshwater had no effect on the seaweed stability, although it reduced the ash content and thereby increased the relative content of ascorbic acid and fatty acids of the biomasses.
Highlights
The seaweeds Porphyra umbilicalis and Ulva fenestrata are promising species for future food use, due to the high content of proteins and the abundance of n-3 polyunsaturated fatty acids (n-3 PUFA), minerals and vitamins
Since chemical reactions are not suppressed to the same degree as mi crobial growth when lowering water activity; and since lipid oxidation can even increase in rate at aw < ~0.3 [14], it is of utmost importance to document how this reaction, as well as its effect on cooxidation of other compounds in seaweed, proceed during and after drying
This study illustrated the formation of lipid oxidation products as well as losses of PUFA, ascorbic acid and colour during the storage of dried Porphyra and Ulva
Summary
The seaweeds Porphyra umbilicalis and Ulva fenestrata are promising species for future food use, due to the high content of proteins and the abundance of n-3 polyunsaturated fatty acids (n-3 PUFA), minerals and vitamins. Despite the high content of unsaturated fatty acids, there are only few studies on lipid oxidation in seaweed [1,2]. The oxidation re action does destroy the fatty acids, causing rancidity, but can co-oxidize pigments and vitamins; altogether reducing both nutri tional and sensorial quality of foods. Freeze-drying has in different studies been found to preserve nutrients, such as polyphenols [11,12], carot enoids [12], ascorbic acid [7], unsaturated fatty acids [7] and amino acids [7,13] in seaweed better than oven-drying (60–70 ◦C). Since chemical reactions are not suppressed to the same degree as mi crobial growth when lowering water activity (aw); and since lipid oxidation can even increase in rate at aw < ~0.3 [14], it is of utmost importance to document how this reaction, as well as its effect on cooxidation of other compounds in seaweed, proceed during and after drying
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