Cost-effective optimized scleroglucan production by Sclerotium rolfsii ATCC 201126 at bioreactor scale. A quantity-quality assessment.

Exopolysaccharide (EPS) secretion by Sclerotium rolfsii ATCC 201126 in submerged cultures, already identified as high-osmolarity responsive, was assessed by reducing C-source without compromising EPS yields. A designed medium with 80 g sucrose L-1 (MOPT80) was tested at 3 L-bioreactor scale at different temperature, agitation, aeration and pH (uncontrolled vs. controlled) values. Optimal operative conditions (200 rpm, 28 °C, 0.5 vvm and initial pH -pHi- 4.5) were validated, as well as the possibility to work at pHi 5.5 to reduce biomass production. Purified EPSs produced in MOPT80 at optimal and other valid operative conditions exhibited refined grade (<1 % proteins and ash, 3-4 % reducing sugars, 87-99 % total sugars). EPS purity, MW and rheological parameters led to discourage pH controlled at 4.5. Relatively constant MW (6-8 × 106 Da) and outstanding viscosifying ability were found. Polyphasic EPS analysis (titre, purity, macromolecular features and rheological fitness) would support to properly select production conditions.

Microbial production of scleroglucan and downstream processing.

Synthetic petroleum-based polymers and natural plant polymers have the disadvantage of restricted sources, in addition to the non-biodegradability of the former ones. In contrast, eco-sustainable microbial polysaccharides, of low-cost and standardized production, represent an alternative to address this situation. With a strong global market, they attracted worldwide attention because of their novel and unique physico-chemical properties as well as varied industrial applications, and many of them are promptly becoming economically competitive. Scleroglucan, a ß-1,3-ß-1,6-glucan secreted by Sclerotium fungi, exhibits high potential for commercialization and may show different branching frequency, side-chain length, and/or molecular weight depending on the producing strain or culture conditions. Water-solubility, viscosifying ability and wide stability over temperature, pH and salinity make scleroglucan useful for different biotechnological (enhanced oil recovery, food additives, drug delivery, cosmetic and pharmaceutical products, biocompatible materials, etc.), and biomedical (immunoceutical, antitumor, etc.) applications. It can be copiously produced at bioreactor scale under standardized conditions, where a high exopolysaccharide concentration normally governs the process optimization. Operative and nutritional conditions, as well as the incidence of scleroglucan downstream processing will be discussed in this chapter. The relevance of using standardized inocula from selected strains and experiences concerning the intricate scleroglucan scaling-up will be also herein outlined.