Production and characterization of dextran from Lactobacillus sp. HH2 isolated from fermented cucumber

Rashwan, Heba Allah Hamada; Amer, Ali ES

doi:10.21608/sjsci.2025.409682.1303

Production and characterization of dextran from Lactobacillus sp. HH2 isolated from fermented cucumber

Document Type : Reviews

Authors

¹ Department of Botany and Microbiology, Faculty of Science, Sohag University, Sohag , Egypt

² BotaDepartment of Botany and Microbiology, Faculty of Science, Sohag University, Sohag 82524, Egypt ny and Microbiology department, sohag university

10.21608/sjsci.2025.409682.1303

Abstract

Dextran is a high molecular weight exopolysaccharide with diverse biomedical applications. Microbial synthesis of dextran using lactic acid bacteria (LAB) provides a scalable and safe alternative to conventional methods. In this study, seven LAB strains were isolated from fermented cucumber and screened for dextran production based on mucoid colony morphology and dextransucrase activity, as determined by the dinitrosalicylic acid (DNS) assay. From amongst the seven LAB isolates of fermented cucumber, dextransucrase activity ranged from 0.0139 to 0.0377 U/mL, with the highest activity from isolate L5 (Lactobacillus sp. HH2). This strain, identified as Lactobacillus species, was confirmed to be the producer of both the enzyme and the polysaccharide. Morphological, physiological, and biochemical analyses indicated acidogenic characteristics typical of the Lactobacillus genus, including catalase-negative and oxidase-negative properties. Dextran was precipitated using 98% chilled ethanol, further purified through sequential ethanol washes, and freeze-dried. Fourier-transform infrared (FT-IR) spectroscopy revealed characteristic α-(1→6) glycosidic linkages, while nuclear magnetic resonance (NMR) spectroscopy confirmed the polymer’s structure with a dominant peak at 3.30 ppm (α-1→6), and secondary signals at 5.3 ppm and 4.03–4.11 ppm corresponding to α-(1→3) and α-(1→2,6) branches. These findings demonstrate the successful microbial production and structural characterization of a bioactive dextran polymer by a Lactobacillus sp. HH2 from fermented cucumber.

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