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    Physicochemical and structural characterisation of a branched dextran type exopolysaccharide (EPS) from Weissella confusa S6 isolated from fermented sausage (Sucuk)
    (Elsevier, 2024) Ozpinar, Fatma Beyza; Ispirli, Huemeyra; Kayacan, Selma; Korkmaz, Kader; Dere, Sevda; Sagdic, Osman; Alkay, Zuhal
    Exopolysaccharide (EPS) producing Lactic Acid Bacteria (LAB) species can be presented in distinct environments. In this study, Turkish fermented sausage (sucuk) was tested for the presence of EPS producer LAB strains and slimy-mucoid colonies were selected for further tests. Among the isolates, Weissella confusa strain S6 was identified and tested for the physicochemical characterisation of its EPS. This strain was found to produce 0.74 g L-1 of EPS in modified BHI medium conditions. Structural characterisation of EPS S6 by 1H and 13C NMR demonstrated that EPS S6 was a highly branched dextran type glucan formed by mainly (1 -* 2)-linked alpha-D- glucose units together with low levels of (1 -* 3)-linked alpha-D-glucose units as branching points. This structure was further confirmed by methylation analysis detected by GC-MS. An average molecular weight of 8 x 106 Da was detected for dextran S6. The FTIR analysis supported the dextran structure and revealed the presence of distinct functional groups within dextran S6 structure. A strong thermal profile was observed for dextran S6 detected by DSC and TGA analysis and dextran S6 revealed a degradation temperature of 289 degrees C. In terms of physical status, dextran S6 showed amorphous nature detected by XRD analysis. SEM analysis of dextran S6 demonstrated its rough, compact and porous morphology whereas AFM analysis of dextran S6 detected in its water solution showed the irregularity with no clear cross -link within the dextran chains. These technological features of dextran S6 suggests its potential to be used for in situ or ex situ application during meat fermentations.
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    Utilisation of an active branching sucrase from Lactobacillus kunkeei AP-37 to produce techno-functional poly-oligosaccharides
    (Elsevier, 2023) Ispirli, Huemeyra; Korkmaz, Kader; Arioglu-Tuncil, Seda; Bozkurt, Fatih; Sagdic, Osman; Tuncil, Yunus Emre; Narbad, Arjan
    Glucansucrase AP-37 was extracted from the culture supernatant of Lactobacillus kunkeei AP-37 and character-istics of the glucan produced by the active glucansucrase in terms of structural and functional roles were determined in this study. A molecular weight around 300 kDa was observed for glucansucrase AP-37 and its acceptor reactions with maltose, melibiose and mannose were also conducted to unveil the prebiotic potential of the poly-oligosaccharides formed via these reactions. The core structure of glucan AP-37 was determined by 1H and 13C NMR and GC/MS analysis which revealed that glucan AP-37 was a highly branched dextran composing of high levels of (1-+ 3)-linked alpha-D-glucose units with low levels of (1-+ 2)-linked alpha-D-glucose units. The structural features of the glucan formed, demonstrated that glucansucrase AP-37 was an alpha-(1-+ 3) branching sucrase. Dextran AP-37 was further characterised by FTIR analysis and XRD analysis demonstrated its amorphous nature. A fibrous compact morphology was observed for dextran AP-37 with SEM analysis whereas TGA and DSC analysis revealed its high stability as no degradation was observed up to 312 degrees C. Finally, the prebiotic potential of the dextran AP-37 and the gluco-oligosaccharides produced with the acceptor reaction of alpha-(1-+ 3) branching sucrase AP-37 were determined and promising results were found for the gluco-oligosaccharides to act as prebiotics.