Storage stability of the dried seaweed species Ulva lactuca and Porphyra umbilicalis subjected to different pre-treatments prior to drying

Abstract

Seaweeds has large potential as a promising biomass, not least in the production of food and food ingredients. In order to have a large-scale production of seaweed-based ingredients and products, cost effective and functioning preservation and storage solutions have to be developed. The production and utilization of seaweed in Sweden is under development and in the Sweaweed project, techniques for cultivation of seaweed species Ulva lactuca and Porphyra umbilicalis are developed and the use of the species for high value products evaluated. In this master thesis project, the storage stability of oven dried Ulva lactuca and Porphyra umbilicalis subjected to different pre-treatments was investigated. To evaluate the storage stability, ascorbic acid content, formation of lipid oxidation products and colour was monitored during a period of 230 days. Additionally, the crude composition was analyzed. Prior to drying the seaweed had been either coated with whey coating or soaked in freshwater. Subsequent storage was performed in either light or darkness in ambient temperature. To evaluate the effect of oven drying per se, samples where freeze dried without any pretreatment and stored under the same conditions. Throughout the storage study there was a loss of ascorbic acid in all samples. Porphyra samples had a higher initial ascorbic acid content than Ulva samples but exhibited a greater loss throughout the storage. Storage under light conditions to some extent increased the loss of ascorbic acid in both Ulva and Porphyra. Coated samples had initially lower ascorbic acid content than non-coated samples but lost less ascorbic acid during storage.Lipid oxidation was analyzed as formation of free aldehydes; malondialdehyde!(MDA), 47hydroxy727hexenal (HHE) and 47hydroxy727nonenal!(HNE). All three aldehydes were detected in all samples in the order of magnitude MDA>HHE>HNE. Light storage increased the formation of aldehydes in oth lva nd Porphyra and after 230 days lowest levels were found in samples stored in darkness. Freeze dried Ulva and Porphyra had higher concentrations of MDA, HHE and HNE than oven dried samples, and were subjected to the largest aldehyde increase in light storage. During storage, samples also lost their green and yellow pigments, especially in light storage, which was visible to the eye especially for freeze dried samples. Overall, the whey coating did not seem to protect the seaweed during drying or storage and freeze drying was not better than oven drying at 40°C in preserving nutritional value based on the parameters analyzed.