The water extracts were then autoclaved and tested as carbon sources in BC production without the addition of any other nutrients. The results obtained (Fig. 1), showed BC productions of 0.81 + 0.04 g L 1 for DOR40 and 0.85+ 0.04 g L 1 for DOR100, which corresponded respectively to 32 and 34% of the production achieved with conventional HS culture medium (w2.5 g L 1). Finally for DOR100H, despite the higher amounts of monosaccharides available, there was no BC production, which was certainly due to the formation or release of organic compounds such as furfural during the hydrolysis step, resulting from sugar degradation and also phenolic compounds, which could have inhibited the metabolism of G. sacchari and consequently BC production [3]. So, unless laborious processes for inhibitors removal are used, the hydrolysed aqueous extract DOR100H is not suited for BC production. However, the BC production values obtained for the two aqueous extracts DOR40 and DOR100 are already promising as these are considerably higher than those previously reported for other residues [22]. Based on these preliminary results it was decided that the optimization studies would be carried out with the DOR40 aqueous extract because its preparation requires less energy consumption to obtain similar results of BC production.
In order to evaluate the behaviour of bacteria in relation to the total and individual monosaccharides content of the culture media during BC production using DOR40, glucose, fructose and xylose contents were analysed.
The results obtained (Fig. 2) show that while BC produced increased overtime until 0.8 + 0.04 g L 1, the concentration in glucose decreased linearly from 10 to 2 g L 1. Fructose (1.55 +0.08 g L 1) seemed to have been nearly depleted by bacteria, during the first 30 h and the concentration of xylose remained roughly constant along the assay. The BC production presented a lag phase in the first 24 h and a linear growth until 72 h when the production entered in a deceleration phase, probably due to the lack of nutrients. However, there was still about 2 g L 1 glucose in the culture medium after 96 h which may suggest that content in sugars was not the limiting factor.