Hydrolysis of Agave fourcroydes Lemaire (henequen) leaf juice and fermentation with Kluyveromyces marxianusfor ethanol production

Abstract

BackgroundCarbon sources for biofuel production are wide-ranging and their availability depends on the climate and soil conditions of the land where the production chain is located. Henequen (Agave fourcroydes Lem.) is cultivated in Yucatán, Mexico to produce natural fibers from the leaves, and a juice containing fructans is produced during this process. Fructans can be hydrolyzed to fructose and glucose and metabolized into ethanol by appropriate yeasts. In Mexico, different Agave species provide the carbon source for (distilled and non-distilled) alcoholic beverage production using the stem of the plant, whilst the leaves are discarded. In this work, we investigated the effect of thermal acid and enzymatic hydrolysis of the juice on the amount of reducing sugars released. Growth curves were generated with the yeasts Saccharomyces cerevisiae and Kluyveromyces marxianus and fermentations were then carried out with Kluyveromyces marxianus to determine alcohol yields.ResultsWith thermal acid hydrolysis, the greatest increase in reducing sugars (82.6%) was obtained using 5% H2SO4 at 100°C with a 30 min reaction time. Statistically similar results can be obtained using the same acid concentration at a lower temperature and with a shorter reaction time (60°C, 15 min), or by using 1% H2SO4 at 100°C with a 30 min reaction time. In the case of enzymatic hydrolysis, the use of 5.75, 11.47 and 22.82 U of enzyme did not produce significant differences in the increase in reducing sugars. Although both hydrolysis processes obtained similar results, the difference was observed after fermentation. Ethanol yields were 50.3 ± 4 and 80.04 ± 5.29% of the theoretical yield respectively.ConclusionsFinal reducing sugars concentrations obtained with both thermal acid and enzymatic hydrolysis were similar. Saccharomyces cerevisiae, a good ethanol producer, did not grow in the hydrolysates. Only Kluyveromyces marxianus was able to grow in them, giving a higher ethanol yield with the enzymatic hydrolysate. The leaves account for a non-negligible weight of the total agave plant biomass, so this work complements the knowledge already developed on agave fermentations by making it possible to produce ethanol from almost the entire plant (stem and leaves).

Fermentable sugars production by enzymatic processing of agave leaf juice

“…Because the agave leaf has no commercial utility, it causes a serious environmental problem (since they are generally burned). At present, there are various research projects for the conversion of this agricultural waste into a value‐added product: ethanol production from agave leaf juice, saccharification of the lignocellulosic residue from bagasse to produce ethanol, and cellulose pulp production from agave leaf bagasse …”

“…The main carbohydrate of agave leaf juice is fructan, which is a polymer of several fructose units and a common glucose residue . Fructan, in general, is a term used for any carbohydrate in which fructosyl‐fructose links constitute most of the glycosidic bonds.…”

“…Microbial inulinases can reach a yield of up to 95 % fructose by a single‐step enzymatic reaction . In fact, there are various reports of agave fructan hydrolysis using inulinases: Avila‐Fernández et al investigated the enzymatic hydrolysis of fructans in tequila production; Corbin et al produced ethanol from agave leaf‐and‐steam juice using a commercial fructanase; Huitrón et al enhanced the ethanol production from raw Agave tequilana juice using exo‐inulinases by culture of Aspergillus niger ; and Villegas‐Silva et al studied the hydrolysis of agave leaf juice and fermentation for ethanol production using a commercial brand inulinase enzyme obtained from Aspergillus niger .…”

Brosimum Alicastrum as a Novel Starch Source for Bioethanol Production

“…The availability of local raw materials is also an important issue that must be addressed when assessing feedstock viability [6]. In this regard, one alternative starch source is the Ramon tree…”

Two Bacillus Species Isolated from Rotting Wood Samples are Good Candidates for the Production of Bioethanol using Agave Biomass

“…Further, these Bacillus strains had ability for simultaneous saccharification and fermentation and were able to convert the reducing sugar to ethanol from the first day of incubation to day seven without pre-treatment of Agave biomass. The enzymatic hydrolysis is helpful to give better ethanol yields than thermal acid hydrolysis after fermentation [23]. During enzymatic hydrolysis, if the biomass is pretreated, the production of ethanol is always higher.…”