Alginate is one of the most abundant marine polysaccharides, which can be degraded into alginate oligosaccharides (AOS) by chemical, physical and biological methods. AOS, linear oligosaccharide composed of guluronic acid and mannuronic acid, have a variety of biological activities such as antimicrobial, anti-inflammatory, and immunoregulatory activities, and these biological activities are closely related to their structural diversity. AOS prepared by different degradation methods have different uronic acid compositions, polymerization degrees and special structures. Therefore, exploring the structure-function relationship of AOS will help to fully understand the activity of AOS and improve its application value. In this paper, the reaction mechanisms of the various methods to prepare AOS, the structures of the resulting products, and the structure-function relationship of AOS are reviewed in order to provide a reference for further research and application of AOS.

The effects of the degradation products of fucosylated exopolysaccharide (DFcP) on the infant fecal microflora were evaluated in vitro in this study. The results of single-strain culture showed that DFcP was selectively utilized by Bifidobacterium longum subsp. infantis ATCC 15697, B. breve ATCC 15700 and Lactobacillus plantarum CGMCC 1.19, and promoted the accumulation of short chain fatty acids (SCFAs). Compared with 2’-fucosylactose (2’-FL), DFcP was utilized more quickly by the fecal microbiota and led to higher levels of SCFA production (34.57 mmol/L, P < 0.05) during in vitro fermentation. The results of single-molecule real-time sequencing (SMRT) showed that DFcP increased the proportion of Firmicutes in the fecal microbiota, up-regulated the relative abundance of Enterococcus, Lactobacillus and Bifidobacterium, which was verified by the results of real-time polymerase chain reaction (PCR). In conclusion, DFcP could be rapidly utilized by the infant fecal microbiota, and significantly regulate its structure and promote the accumulation of the beneficial metabolite SCFAs. This study reveals the potential of DFcP as new prebiotics, which provides a theoretical basis for further development of novel fucosylated oligosaccharide resources.