SCLEROGLUCANS PRODUCED AT BIOREACTOR SCALE WITH ALTERNATIVE CARBON SOURCES: DIFFERENTIAL RHEOLOGICAL BEHAVIOR AGAINST ALKALI, TEMPERATURE AND CHAOTROPS

CASTILLO NA; FARIÑA JI

Bs. As.

Congreso; II Workshop on Bio-degradable Polymers and Biocomposites III Workshop BIOPURFIL, Bio-based Polyurethane Composites with Natural Fillers; 2015

BioPoli

INTRODUCTION. Synthetic petroleum-based polymers and natural plant polymers have the disadvantage of restricted sources, in addition to the non-biodegradability of the former ones. Scleroglucan is a high molecular weight, non-ionic branchedexopolysaccharide (EPS). When dissolved in water, scleroglucan adopts a highlyordered, triple-helical conformation and a semi-rigid structure. The length ofpolymer chain, molecular mass, degree of branching and degree of polymerization may differ however, depending on the producing microbial strain, fermentation process (culture media, fermentation time, etc.) and the recovery method used. Furthermore, any variation on these conformational features is critical, because they are responsible of the marked viscosifying ability, outstanding rheological behavior and emerging successful applications of scleroglucan. In this work, the viscosifying ability and rheological stability of aqueous solutions of EPS samples (obtained in different culture media) against extreme alkalinities, temperatures and DMSO treatment were evaluated. MATERIALS AND METHODS. Scleroglucan was produced by Sclerotium rolfsii ATCC 201126 during 72 h, at bioreactor scale. Operational conditions for production and recovery of polymer samples were set as previously described. EPSs were obtained using 4 different culture media: MOPT (w/ 150 g/L sucrose), MP20 (w/ 20g/Lsucrose), M-St and M-Mol (~MP20 w/ C-starch or C-molasses). Purified EPSs were used to prepare 2 g EPS/L aqueous solutions. Viscosifying ability and rheological stability of these EPS solutions were tested after thermal (thermoblock: 150°C, 15 min; autoclave: 121°C, 15 min), alkaline (NaOH 0.01, 0.05, 0.1 and 0.2 M , 10 min) or DMSO (5, 10, 15, 25 and 50% w/w) treatments. Rheological measurements were performed before and after treatments and the consistency coefficient (K) and flow behavior index (n) were calculated, according to the Ostwald-de-Waele model. RESULTS AND DISCUSSION. Rheological measurements of the four non-treated EPS samples showed the following pattern of K (mPas.s^n), depending on the EPS source: M-Mol (975.4) > MOPT (791.8) ~ M-St (784.4) > MP20 (480.1), with n values between 0.20 and 0.28. For all EPS aq. samples, K value increased between 40 and 90% (n changed from 0.24 to 0.17) by autoclave thermal treatment. Conversely, thermoblock heating induced a general sharp drop in viscosity. Treatment with NaOH concentrations between 0.01 and 0.1 M produced a 2-fold increase in K values for EPSs produced in MOPT (n = 0.10-0.12) and M-Mol (n = 0.13-0.15), as compared to the non-treated EPSs. Meanwhile, the increase in viscosity varied between 53-91% for EPS produced in M-St, and between 19-53% for MP20-EPS. In all cases, the higher K values were obtained at the lower NaOH concentration (0.01M), but these values drastically decreased with the addition of 0.2 M NaOH. On the other hand, the higher tested DMSO concentrations induced the greater increases in K (40-85% for EPS M-St, and up to 50% for the rest of EPSs) compared to non-treated polymers. These results allowed evidencing variations in rheological properties of scleroglucan samples obtained under different cultivation conditions. That may be related to variances in EPS conformational features, which could be differently affected when exposed to high temperature, alkali or DMSO. Increased viscosity (> K, < n) might be related to a macromolecular expansion, whilst viscosity drops would result from the triplex dissociation (denaturation).This characterization becomes essential when analyzing EPS biotechnological applications.