Sugar beet pulp (SBP), a by-product of the sugar beet industry, is the fibrous material left over after the sugar is extracted from sugar beets and is mainly composed of cellulose, hemicellulose, and pectin. Beet pulp is used in countries with an intensive cattle raising industry, as livestock feed. In other countries, it is dumped in landfills. However, SBP can be an important renewable resource and its bioconversion appears to be of great biotechnological importance [69].

There are several reports on the pretreatments applied to SBP. Autoclaving of SBP at 122 °C and 136 °C for 1 h was reported to change its composition and physico­chemical properties causing increased swelling and improved solubility of pectins and arabinans [70]. Ammonia pressurization depressurization (APD) pretreatment where SBP is exploded by the sudden evaporation of ammonia, was found to sub­stantially increase hydrolysis efficiency of the cellulose component [71]. Recently, Kuhnel et al. [72] examined the influence of six mild sulfuric acid or hydrother­mal pretreatments at different temperatures on the enzymatic degradability of SBP and they found that optimal pretreatment at 140 °C of 15 min in water was able to solubilize 60 % w/w of the total carbohydrates present, mainly pectins.

Taking into consideration that SBP is carbohydrate-rich with a high carbon-to — nitrogen ratio (C/N, 35-40), that sugar beet farming is a widespread and already mature industry, and that beet pulp is abundant and cheap, this coproduct has potential for use as a renewable biomass feedstock for microbial fermentations for biopolymer production [71]. On the other hand, there are very limited numbers of reports on the use of SBP as a resource for microbial polysaccharide production. Yoo and Harcum investigated the feasibility of using autoclaved SBP as a supplemental substrate for xanthan gum production from X. campestris and they reported a production yield of

0. 89 g xanthan per gram of SBP in 4 days of fermentation time [54]. Sogutgu et al. [63] investigated the effects of autoclaving, reducing the particle size by milling and accessibility of SBP for EPS production by halophilic Halomonas sp. AAD6 cultures. In this study, milling of dried SBP in a mortar grinder, supplying SBP in dialysis tubes rather than directly in culture media and autoclaving SBP separately, and then adding to the fermentation media were all found to increase the EPS yields.