Co-cultures for simultaneous production of ethanol and xylitol were studied under different operation bioreactor modes using Candida tropicalis IEC5-ITV and Saccharomyces cerevisiae ITV01-RD in a simulated medium of sugarcane bagasse hydrolyzates. Xylitol and ethanol tolerance by S. cerevisiae and C. tropicalis, respectively, was evaluated. The results showed that C. tropicalis was sensitive to ethanol concentrations up to 30 g/L, while xylitol had no effect on S. cerevisiae viability and metabolism. The best condition found for simultaneous culture was S. cerevisiae co-culture and C. tropicalis sequential cultivation at 24 h. Under these conditions, productivity and yield for ethanol were Q EtOH = 0.72 g L −1 h −1 and Y EtOH/s = 0.37 g/g, and for xylitol, Q XylOH = 0.10 g L −1 h −1 and Y XylOH/S = 0.31 g/g, respectively; using fed-batch culture, the results wereand Y EtOH/s = 0.57 g/g, respectively. Maximum volumetric productivity in continuous multistep cultures of ethanol and xylitol was at dilution rates of 0.131 and 0.074 h −1 , respectively. Continuous multistep production, Q EtOH increased up to 50% more than in fed-batch culture, even though xylitol yield remained unchanged.

The search for new ethanol production technologies is due to this biofuel being a renewable and environmentally friendly option. Immobilized cell systems for ethanol production have been studied; however, the phenomenon involved in cell sorption on raw materials has been poorly explored. Therefore, this work evaluates P. stipitis immobilization on sugarcane bagasse pretreated with sulphuric acid, as well as ethanol production in batch culture. The results obtained showed that the Guggenheim-Anderson-de Boer (GAB) model explained the sorption phenomenon. The selected inoculum size for immobilization was the same as the monolayer sorption capability (1.17 gl-1). Using 1:100 g ml- 1 solid-liquid ratio, at 250 rpm, ethanol yield and productivity of 0.404 gg-1 glucose and 0.41 gl-1h-1 were obtained, respectively. The immobilized systems were stable for up to twenty-five repeated batches (36 h each). Ethanol production was increased from the first to the twenty-fifth batch (18.1 and 24.7 gl-1 ethanol). The use of complex media, such as molasses “B” or sugarcane hydrolyzates, caused an increase in process efficiency 2.4 and 1.8-fold respectively, compared with free cells systems. Biotechnological ethanol production from lignocellulosic hydrolyzates could be improved by the use of the immobilization cell sorption on pre-treated raw materials.

Acetic acid can be directly produced from glucose in one-step fermentation by using yeasts of the genus Brettanomyces bruxellensis, hence increasing the industrial application to manufacture products with simplified bioprocesses. Thereby, this work evaluates the influence of initial glucose concentration on the growth and acetic acid production by B. bruxellensis. The results obtained confirmed the presence of Crabtree effect on B. bruxellensis under low glucose concentrations. The maximum acetic acid concentration reached was 15.4 g•L −1 starting with 100 g•L −1 leading to a product yield of 0.154 g•g −1 and a specific acetic acid production rate of 0.05 g•g −1 •h −1. The results also indicate that after reaching the acetic acid critic threshold of 4 g•L −1 the metabolism can induce the growth second phase even residual glucose was present on the culture media at high starting glucose concentrations. Additionally, it was observed a lineal relationship between cell viability and acetic acid production.