The bioethanol production from agave juice batch fermentation process is shown. For this work, three yeast strains isolated from agave juice were studied for their fermentative capacity. The strains (S1, S2 and S3) were identified by biochemical and molecular tests [15]. The experiments were performed using agave juice supplemented with sufficient ammonium sulphate, for maintaining a good performance of the yeast strains. For fermentation medium, sugar concentration of the agave juice was adjusted to 12 °Brix (95±5 g/L reducing sugar) and then supplemented with 1g/L of ammonium sulphate. Culture media were sterilized at 121 °C for 15 min. The pH of the unadjusted juice was 4.2. This fermentation medium was similar to the must typically used in industrial distilleries for obtain alcoholic beverage. The fermentations were carried out under anaerobic conditions at 35 °C and 250 rpm in a 3 L bioreactor (Applikon, Netherlands). The inoculation level was 20 million cells/mL. Two fermentations were performed with each yeast.

Each must was fermented for 72 h, and sampling was performed every 2 h during the first 12 h of fermentation, then every 4 h during the following 48 h, until the last sampling event at 72 h. Biomass concentration was obtained by dry weight measurement. Reducing sugar concentration was determined by the DNS method modified and glucose, fructose and

glycerol concentration was determined by HPLC [15]. Samples were micro-distilled and ethanol concentration was determined in distillates by using the potassium dichromate method [19].

Fermentation Kinetic Analysis — The evolution of biomass, sugar consumption and ethanol production versus time were plotted in Fig. 1 and Table 1, showing the kinetic parameters of each strain. All Saccharomyces strains grew faster reaching a biomass concentration level of 4­5.3 g/L by approximately 12 h and sugar was completely depleted by 18-24 h of the fermentation (Figure 4). The S1 and S2 strains showed a higher ethanol concentration and sugar consumption than S3 (Figure 4 and Table 4).

Growth and ethanol yields were different: 0.046-0.059 g/g and 0.47-0.49 g/g, respectively (Table 4). Statistical analysis (95% LSD) showed significant differences between yeast strains in all kinetic parameters (Table 4). S. cerevisiae S1 strain presented a higher value of maximum specific growth and sugar consumption than S2 and S3 strains. Likewise, S1 and S3 strains showed a high maximum specific ethanol rate (Table 4).