The HPLC and NMR results from the present work confirmed the heterogeneity of the EPS (3 different sugar moieties with different molar ratios), which agrees with the other reported mannan polysaccharides. The 1H and 13C NMR chemical shifts are comparable with literature reports of other similar EPS or oligosaccharides, where complex structures are identified by NMR too (Casillo et al., 2021; Chatterjee et al; 2018). Besides, our 2D-NMR analysis supported EPS heterogeneity, identifying different types of monomer linkages. Casillo, A., Fabozzi, A., Russo Krauss, I., Parrilli, E., Biggs, C. I., Gibson, M. I., … Corsaro, M. M. (2021). Physicochemical Approach to Understanding the Structure, Conformation, and Activity of Mannan Polysaccharides. Biomacromolecules, 22(4), 1445–1457. doi:10.1021/acs.biomac.0c01659. Chatterjee, S., Mukhopadhyay, S. K., Gauri, S. S., & Dey, S. (2018). Sphingobactan, a new α-mannan exopolysaccharide from Arctic Sphingobacterium sp. IITKGP-BTPF3 capable of biological response modification. International Immunopharmacology, 60, 84–95. doi:10.1016/j.intimp.2018.04.039 •
Chemical shift similarity is not sufficient to identify monosaccharide and linkage in a polysaccharide repeating unit. The evidences for the partial structure given are not convincing. If the authors do not add methylation analysis and perform full NMR spectral analysis, the claims about structure determination should be removed from the manuscript. They deleted erroneous information about mannose residues, but came up with new conclusions about mannose identity and linkages based solely on chemical shift of anomeric proton/carbon.The information contained in the other 2D spectra was not exploited to provide structural information.