Effects of cultivar selection, cultivation region and harvest timing on the structure and properties of carbohydrates from Saccharina japonica

Abstract

The study aimed to explore the difference of yields, structures, and functions of three carbohydrates in Saccharina japonica (S. japonica), considering the differences of cultivars of Haiza (the northern cultivar) and Puke (the southern cultivar), cultivation regions (the north, the south, and the transplanted Puke from south to north), and harvesting times during their whole cultivation. The yield of mannitol was significantly higher in samples cultivated in the north region (5.07–27.82 %) compared to those from the south (2.34–3.37 %), and for both cultivars the optimal yield was in May and June. The molecular weight of alginate was lower in Puke but higher in both Haiza and the transplanted Puke. The mannuronate/guluronate ratio of alginate noticeably deceased from levels of 2.28–2.40 to levels of 1.68–1.93 after transplantation Puke from the south to north, which indicated the possible upregulation of the expression of genes encoding mannuronate C5-epimerases in colder temperature cultivation. Meanwhile, different fucoidan samples showed diverse monosaccharide composition, sulfate content, sulfation positions, and antioxidant activities. Fucoidans from Haiza showed better ABTS and hydroxyl radical scavenging ability. The correlation analysis indicated that the fucose content was positively correlated with ABTS radical scavenging ability (R = 0.576), while fucose and sulfate group contents were negatively correlated with the hydroxyl radical scavenging ability (R = 0.581 and R = 0.829). Overall, this study deepened the understanding of carbohydrates diversity in S. japonica and provided a scientific foundation for optimizing its cultivation strategies.