Rheological properties of the structurally characterized biopolymers produced by Leuconostoc strains isolated from wild strains in Northern Argentina.

LOBO, R.E.; SANTOS GARCÍA M.; HEBERT, E.M.; RODRÍGUEZ‐CABELLO J.C.; TORINO, M.I.

Virtual

Congreso; LVII SAIB Meeting - XVI SAMIGE Meeting SAIB - SAMIGE Joint Meeting online; 2021

Certain lactic acid bacteria (LAB) can produce anextracellular αDglucan homopolysaccharide (HoPS) formed by glucose units whengrowing in sucrose-enriched media. HoPS from LAB are natural bio-thickenersthat improve rheological properties by providing viscosity and reducingsyneresis. The structural diversity of biopolymers is linked to their vastcommercial value and applications in the food, cosmetic, medical, andbiotechnology fields, reaching much attention in recent years. Previously, wereported the bioprospection of thirty-one HoPS producer LAB strains, isolatedfrom wild fruits of northern Argentina and belonging to the Weisella andLeuconostoc (Ln.) genera in a sucrose-enriched MRS medium (MRS-S, 4%). Inaddition, some techno-functional properties of selected HoPS identified asglucans dextran-type were studied. Currently, we aimed at the chemicalstructure and rheological properties of HoPS from selected Ln. strains (Ln.pseudomesenteroides F-G2-22 and Ln. citreum F-Cq1-496) since their high polymerproduction in MRS-S. The two studied HoPS were isolated and purified from MRS-Sagar (gr.Kg-1 medium) after 48 h at 30 °C. The molecular structure was studiedby HPLC (Knauer Wellchrom with a Waters Ultrahydrogel column), NMR (400 MHz,Agilent Technologies), DRX (Bruker D8 Discover A 25), ξ (Zetasizer Nano ZS,Malvern Instruments Ltd.), and rheological properties at differentconcentrations: 1, 2.5, and 5 % (TA Instruments, mod. ARES-G2). F-G2-22 andF-Cq1-496 strains grew up in MRS-S agar produced 6.27 and 6.78 gr.Kg-1 of HoPS,respectively. In addition, we not observed contaminants in the samples(protein, nucleic acid, or pigment by UV spectra). These HoPS were biopolymersof high molecular weight: 7442.7 kDa and 6857.3 kDa for F-G2-22 and F-Cq1-496 strains,respectively. NMR studies revealed typical signals of a linear dextran withoutbranches structure. Only a single α-1,6 glycosidic binding signal ( ̴ 5 ppm) inboth biopolymers were observed. On the other hand, the XRD spectra reflected asemi-crystalline arrangement with crystallinity indices lower than 30%. Also,both HoPS exhibited neutral charges in their structures (ξ ̴ 0 mV) commonlyobserved in glucan polysaccharides. The oscillatory rheology, the storagemodulus G´ and the loss modulus G" showed G´ < G´´ at low oscillationfrequencies. A decrease in the modules´ slope at higher frequencies waspossible to exhibit typical viscoelastic fluids characteristics in all studiedsolutions. Dextran is produced by many food-grade organisms such as LAB. Itimproves the texture of products containing plant protein to make veganreplacements for dairy products. Our results suggest that the biopolymersproduced by the Ln strains possess a dextran polymeric structure similar toeach other. The rheological properties of both studied biopolymers confer greatpotential to be used as bio-additives in the food industry.