Xylitol production by Ca-alginate entrapped cells: comparison of different fermentation systems

Candida guilliermondii cells were entrapped in Ca-alginate beads and used for xylitol production from concentrated sugarcane bagasse hemicellulosic hydrolysate in three different fermentation systems, namely 125-ml Erlenmeyer flasks (EF), 2.4-l stirred tank reactor (STR) and 2.4-l basket-type stirred tank reactor (BSTR). The EF system provided a xylitol production of 21.0 gP l−1, a product yield based on xylose consumption of 0.54 gP gS−1, and an overall production rate of 0.44 gP l−1 h−1 after 48 h of fermentation. By the STR system, 23.5 gP l−1 was produced after 60 h of fermentation, corresponding to a yield of 0.58 gP gS−1 and a production rate of 0.39 gP l−1 h−1. As the average volume of the beads decreased by 10.7% (p<0.05) during this fermentation, a basket was fitted into the reactor vessel to prevent the beads abrasion and thus maintain their integrity. However, the xylitol yield (0.46 gP gS−1), production rate (0.21 gP l−1 h−1) and concentration (15.0 gP l−1) attained by this system were affected by mass-transfer limitations.