Production and structural characterisation of dextran from an indigenous strain of Leuconostoc mesenteroides BA08 in Whey

Abstract

In this work, the production of dextran was carried out in whey-supplemented media using Leuconostoc mesenteroides BA08. Different growth and nutritional parameters were optimised to maximise the dextran production. Batch production in whey-based media under optimised nutritional and growth conditions yielded a dextran concentration of 17.25 g/L. Structural analysis of the purified polymer by FT-IR, 1D 1 H and 13 C nuclear magnetic resonance methodology revealed that polymer was a linear dextran having 93% a-(1?6) linkage in the main chain. The morphology of the dried dextran and dextran-producing cells was also studied by scanning electron microscope which showed a granular and porous or weblike structure, respectively. The results obtained showed that the industrial whey supplemented with nutrients such as sucrose, yeast extract and K 2 HPO 4 can serve as an ideal growth medium for dextran production. The optimised fermentation and nutritional parameters can be further scaled up to establish the potential for the commercial production of food-grade dextran from whey as part of a novel cost-effective and environment-friendly approach.

Dextran: Sources, Structures, and Properties

“…Bacterial dextransucrases, located extracellularly, are responsible for hydrolyzing sucrose in its fructose and glucose monomers, forming an intermediate with glucose (glycosyl-enzyme) to later carry out their polymerization and form dextran [10], while the resulting fructose enters the bacteria through PTS to meet its metabolic demand [11], as shown in Figure 2. LAB that report dextran production are mainly of the genus Leuconostoc, Weissella, Lactobacillus, and Streptococcus [10], which have been isolated from different plant sources (e.g., Agave salmiana and pummelo) [12,13] and fermented products (e.g., rice batter, cabbage, idli batter, and pickles) [14][15][16][17]. However, dextran can also be synthesized via enzymatic, directly using dextransacarases (sucrose: 1,6-α-D-glucan 6-α-D-glucosyltransferase, EC 2.4.1.5) [18], which polymerize the glucoses of the sucrose in dextran, as shown at the top of Figure 2.…”

“…There are even reports that, in general, all low molecular weight polysaccharides have a higher solubility compared to long chain polysaccharides [43]. There is no direct relationship between the characteristics of the molecule and the variation of the properties [14,35,41,68,79]. However, regardless of the degree of solubility, dextrans are considered soluble EPS due to their ability to incorporate large amounts of water and form hydrogels [80].…”

Extracellular polysaccharides produced by bacteria of the Leuconostoc genus

“…However, there is no single set of culture conditions that guarantees high product yields, since organisms differ in their attitudes towards these critical factors for maximum EPS production (Kumar et al 2007). At the same time, the production of most EPS, including dextran, can also be characterized by a number of common features and preconditions, such as the growth-associated nature of the process, where the maximum of product is reached at the early stationary phase, the need for elevated C/N ratios and temperature below the optimal for cell growth (Barcelos et al 2019;Kumar et al 2007;Lule et al 2016;Onilude et al 2013;Vijayendra and Sharath Babu 2008). The observed relationships between dextran molecular weight distribution, reaction temperature, dextransucrase and sucrose concentrations observed in most cases of cellfree enzymatic syntheses are also of a common nature (Falconer et al 2011;Kanimozhi et al 2019).…”

Production of biodegradable microbial polymers from whey

“…As a biodegradable, biocompatible and easily soluble polymer, dextran is widely used in the food and pharmaceutical industries, medicine (blood volume expander) and biochemistry (chromatographic media), etc. (Santos et al 2005;Lule et al 2015;Lule et al 2016). As with other biopolymers, a greater use of renewable and less expensive resources is important for the microbial production of dextran.…”

“…Using other producers L. mesenteroides NCDC 744 and L. mesenteroides NCDC 745, 12.7 g/L (0.79 g/L/h) and 10.51 g/L (0.66 g/L/h) of dextran were obtained respectively in partially deproteinised paneer whey medium with 10% sucrose, 0.1% yeast extract and 0.1% K 2 HPO 4 (Lule et al 2015). Increased concentration of dextran (17.25 g/L) was observed under optimised (15% sucrose, 25 °C) conditions using the strain L. mesenteroides NCDC 7459 (BA08) (Lule et al 2016). Recently, quite good results have been achieved with the use of producer strains L. mesenteroides NRRL B512F, NCIB 8023 and NRRL B12, to obtain 16.35 g/L (0.68 g/L/h),15.89 g/L (0.66 g/L/h) and 16.28 g/L/h (0.68 g/L/h) respectively in batch fermentation (30 °C) and the medium containing a milk whey permeate (15 g/L), sucrose 20 g/L and yeast extract (15 g/L (Esmaeilnejad-Moghadam et al 2019).…”