Revalorization of inexpensive carbon sources and agroindustrial by-products for scleroglucan production by sclerotium rolfsii atcc 201126 at fermenter scale

Abstract

Scleroglucan, a neutral hydrosoluble exopolysaccharide (EPS) is produced by submerged fermentation with filamentous fungi of the genus Sclerotium. Because of its wide variety of actual or potential applications, several industries focused their attention on this biopolymer. Large-scale production at fermenter scale has not yet been faced in our country, being an interesting field for competition particularly considering its high added-value and its monopolized production and commercialization by foreign industries. In this context, the examination of possibilities for biopolymer local production, especially at low cost, has become imperative. In a previous study we evaluated scleroglucan production by Sclerotium rolfsii ATCC 201126 at shake flask scale using 9 different C-sources, being sucrose, maltose, corn starch and sugarcane molasses the preferred substrates. In this work, sucrose, corn starch and sugarcane molasses were evaluated as C-sources for scleroglucan production at fermenter scale, due to their low cost and high availability. Two-day-old mycelia grown at 30ºC on PM20 agar were used for seed cultures after homogenization in liquid medium. Seed cultures were placed in Erlenmeyer flasks containing PM20 and incubated at 220 rpm and 30ºC for 48 h. They were used to inoculate (10%, v/v) the different tested culture media. Batch fermentation was carried out under optimized conditions for 72 h in a 5-L stirred-tank bioreactor with a working volume of 3 L. Samples were withdrawn every 12 h and biomass, EPS, starch, glucose and reducing sugars were determined. Once fermentation was stopped, scleroglucan obtained with the different substrates was recovered, purified and quantified following the protocol described by Fariña et al. (Carbohydrate Polymers, 2001, 44: 41-50). Yield (Yp/c) volumetric productivity (Pr), specific productivity (Pr/x), and recovery efficiency (r.e.) were calculated. The highest scleroglucan production parameters were achieved when using corn starch as C-source (EPS=7.95 g/L; Yp/c=0.40; Pr=0.110 g/L.h; Pr/x=0.018; r.e.=51.53%). Sugarcane molasses led to 5.11 g/L of EPS with an Yp/c=0.28, Pr=0.071 g/L.h, Pr/x=0.013 and r.e. of 33.16%. Meanwhile, sucrose allowed to produce 6.87 g/l of EPS with an Yp/c=0.34, Pr=0.095 g/L.h, Pr/x=0.014 and an r.e. of 28.48%. Based on these results and given the similar or better performance when using these substrates instead of the commonly used sucrose, the possibility to produce scleroglucan with S. rolfsii ATCC 201126 from molasses and starch represents a promising biotechnological alternative for the development of a sustainable production process. It opens the possibility to manufacture a high added-value bioproduct from economic or industrial by-product substrates. Additionally, although with moderately lower production parameters, the use of molasses may also represent an advantage from the environmental impact point of view.