Fermentable sugars production by enzymatic processing of agave leaf juice

Abstract

The Mexican mezcal industry annually processes approximately 2.92 × 105 t of mezcal agave, generating roughly 1.46 × 105 t of agave leaves per year, which represents a potential carbon source of at least 8170 t via enzymatic processing of agave leaf juice. This carbon source is considered an attractive alternative to produce biofuels and/or chemical products since it is produced and used without adversely affecting the environment. The aim of this investigation was to determine the effect of temperature, pH, enzyme concentration, and bioreaction time on the enzymatic hydrolysis of agave leaf juice enriched in fructan to maximize the fermentable sugars production from three varieties of mezcal agave, using a low‐cost commercial brand of hydrolase. This process generated a sugar‐enriched juice of 80.07–136.12 g/L of reducing sugars. A Box‐Behnken experimental design and a mathematical surface response analysis of the hydrolysis were used for process optimization.

Elucidation of native California Agave americana and Agave deserti biofuel potential: Compositional analysis

“…americana harvested from Mexico. Given that the leaf base was similar in soluble carbohydrate content to the stem [ 19 ], these compositions were also comparable to stem juice compositions from other studies. In their article, Li et al [ 16 ] noted that their 4–5 year old A .…”

“…Although these amounts rivaled the sugar content of hardwood poplar, with an average combined cellulosic and hemicellulosic composition of 64.8% [ 40 ], and exceeded those of the ubiquitous corn stover and the energy crop switchgrass by about 4–11% [ 40 ], it should be noted that the total combined carbohydrate in Table 1 includes the hydrolyzed fructans from the WSC and were derived from the sugar-rich leaf bases [ 19 ]. With declining soluble sugar content away from the leaf base [ 19 ], the WSC would decline when the whole leaf was analyzed. Nevertheless, when the WSC, which constitutes a significant portion of available carbohydrate associated with the bagasse [ 16 ], was factored into consideration, agave continues to look promising as a potential biofuel feedstock.…”

“…deserti juice, comprised of glucose, fructose, and sucrose, were 21.3 g/L and 33.8 g/L, respectively. Assuming that other sugar monomers (e.g., arabinose, mannose, galactose) were present in minor to negligible amounts, the work by Gonzalez-Llanes et al [ 19 ] indicated a leaf base reducing sugar concentration of 19.7 g/L for their 8 year old A . americana harvested from Mexico.…”

“…americana , a potential native species of the State, was investigated by Corbin et al [ 15 ] and Rijal et al [ 17 ] their agave species were from Australia. Gonzalez-Llanes et al [ 19 ] also studied the reducing sugars of A . americana leaves in their enzymatic hydrolysis of mezcal-producing agaves, but their samples were sited in Mexico.…”

“…Though A. americana, a potential native species of the State, was investigated by Corbin et al [15] and Rijal et al [17] their agave species were from Australia. Gonzalez-Llanes et al [19] also studied the reducing sugars of A. americana leaves in their enzymatic hydrolysis of mezcal-producing agaves, but their samples were sited in Mexico. In the United States, Li et al [16] established the composition of 4-5 years old A. americana that was sourced from San Jose, California, and found the plant to be a promising feedstock candidate as its unpretreated agave leaf and stem bagasse when subjected to enzymatic hydrolysis at enzyme loading of 150 mg/g of structural carbohydrates resulted in high total sugar yields exceeding 70 wt.% [20].…”