Agave juice bioethanol production from involves multiple steps: at harvest, fermentable sugars are obtained from heads of the agave plant by steaming, milling and pressing. During the steaming process, the polysaccharides (fructans) are hydrolyzed into a mixture of sugars consisting of fructose mainly. After fermentation, the alcohol from the must is purified by distillation and dehydration for obtaining anhydrous ethanol.

Alcoholic Fermentation is one of the most important stages in the bioethanol process, as sugars (mainly fructose) are transformed into ethanol and CO2. Agave juice can be fermented by inoculation (with selected microorganisms) or spontaneously (without inoculums). Significant differences were observed between fermentation conducted with controlled microorganism or inoculated media and spontaneous or no inoculated media. The introduction of selected strains allows fermentation to be regulated and accelerated. Inoculation of culture media with starter cultures allows a high population of selected strain, thereby assuring it dominance. The results are quicker ethanol synthesis, shorter fermentation time, and higher productivity.

Knowledge of physiological behavior of indigenous tequila yeast used in the agave juice alcoholic fermentation process for obtaining bioethanol is still limited. The raw material and physiochemical and biological conditions have significant impact on the productivity fermentation process. For these reasons, a better knowledge of the physiological and metabolic features of these yeasts in agave juice fermentation is required. A study of bioethanol production from Agave tequilana Weber var. azul juice fermentations is presented below. For this, the alcoholic fermentation of Agave tequilana Weber var. azul juice was carried out in batch and continuous modes of fermentation process.

a. Agave tequilana Weber var. azul juice characterization

The Agave tequilana Weber juice used in the experimentation was supplied by a distillery. The sugar concentration of the agave juice was 20 °Bx and pH was 4.0. In the distillery, the agave plants are cooked in an autoclave at 95 to 100°C for 4 hours.

Amino acid analyses were determined by HPLC [17]. The acid hydrolysis of agave juice was performed as reported by Umagath et al. [18].

Table 3. Amino acid composition of grape and agave juices.