Xiong Li,Chuyi Li,Yizhou Liu,Gang Han,Congyu Lin,Xiaoli Chen,Jian Mao
Carrageenans were widely utilized as thickening and gelling agents in the food and cosmetic industries, and their oligosaccharides have been proven to possess enhanced physicochemical and biological properties. In this study,Shewanella sp.LE8 was utilized for the depolymerization of κ-, ι-, and λ-carrageenan under conditions of fermentation. During a 24-h fermentation at 28 °C, the apparent viscosity of κ-, ι-, and λ-carrageenan decreased by 53.12%, 84.10%, and 59.33%, respectively, accompanied by a decrease in storage modulus, and loss modulus. After a 72-h fermentation, the analysis of methylene blue and molecular weight distribution revealed that ι-carrageenan was extensively depolymerized into smaller polysaccharides byShewanella sp.LE8, while exhibiting partial degradation on κ- and λ-carrageenan. However, the impact ofShewanella sp.LE8 on total sugars was found to be limited; nevertheless, a significant increase in reduced sugar content was observed. The ESIMS analysis results revealed that the purified components obtained through ι-carrageenan fermentation for 72 h were identified as tetrasaccharides, while the two purified components derived from λ-carrageenan fermentation consisted of a hexasaccharide and a tetrasaccharide, respectively. Overall, the present study first reported the depolymerization of ι-and λ-carrageenan byShewanellaand suggested that theShewanellacould be used to depolymerize multiple carrageenans, as well as complex polysaccharides derived from red algae, to further obtain their oligosaccharides.
Carrageenan oligosaccharides have attracted significant attention due to their excellent biological activities, and they can be produced by carrageenases. In this study, a novel marine bacterium, Shewanella sp. LE8, was used to enzymatically degrade carrageenan, and the κ-, ι-, and λ-carrageenases produced by the bacterium were characterized. The crude enzyme derived from media exhibited κ-carrageenase activity, indicating its natural secretion during growth and proliferation. According to the results of molecular weight distribution from HPGPC, λ-carrageenan could be degraded by Shewanella sp. LE8 cells in both 20 mM Tris-HCl buffer and PBS, while ι-carrageenan can only be hydrolyzed in PBS environment, indicating the activation of ι-carrageenase in Shewanella sp. LE8 was dependent on the presence of Na + ions. The components of carrageenan hydrolysates were determined by ESIMS, and results revealed that κ-carrageenan hydrolysates were primarily consisted of G4S-DA, [G4S-DA] 2 and [G4S-DA] 3 , while ι-carrageenan hydrolysates were predominantly composed of [G4S-DA2S] 2 . Moreover, the fragment ions of λ-carrageenan revealed that the hydrolytic process not only encompasses enzymatic cleavage of glycosidic bonds but also involves the participation of sulfatase. The precise structure was further elucidated through NMR analysis, confirming that the end-products of ι-carrageenase were neoι-carratetraose. The results highlight the potential of Shewanella sp. LE8 for industrial applications in the production of ι-carrageenan oligosaccharides.
危险品化学品经营许可证（带存储）