Abstract
The brown alga Saccharina japonica is widely consumed in Asian countries, and post-harvest drying methods such as sun drying and oven drying are commonly used to extend the shelf life of S. japonica. Thus, the present study analyzed the ethanol extract and organic solvent fractions of S. japonica to examine the effects of UVA and heating on certain bioactive compounds (fucoxanthin, phlorotannin compounds, and total antioxidants) during the drying process. The fucoxanthin contents in the ethanol extract and different solvent fractions significantly decreased in response to UVA. However, fucoxanthin in the ethanol extract and other fractions showed resistance to thermal treatment. It is noteworthy that the total phlorotannin content (TPC) in the ethanol extract and all fractions showed an approximately 2.5-fold increase upon UVA radiation. The TPC also increased in all samples exposed to high temperatures, except for those in the chloroform fraction. The total antioxidant capacity (TAC) also exhibited significant increases in a pattern similar to the TPC. The findings demonstrate that UVA exposure and heating stimulated the degradation of fucoxanthin while it increased the TPC and TAC in the extract and fractions of S. japonica.
Highlights
Kelp is a type of large brown seaweed that grows in shallow, nutrient-rich saltwater near coastal fronts
The ethanol extract of S. japonica (2.5 kg wet weight) yielded 88.37 g of crude extract (3.58% yield), among which 50 g was used for fractionation
Phenolic compounds and carotenoids have a high solubility in non-polar solvents due to their low polarity
Summary
Kelp is a type of large brown seaweed that grows in shallow, nutrient-rich saltwater near coastal fronts. Known as kumbo in Japanese, dasima in Korean, and haidai in Chinese, has a long consumption history in those East Asian countries. There are about 30 different species of kelp, among which Saccharina japonica (previously known as Laminaria japonica) is one prominent species that is widely consumed and extensively cultivated in Korea. As dried kelp is generally consumed in South Korea, the drying process is carried out through air drying under natural sunlight after harvesting, followed by heat drying at a high temperature in a drying machine
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