Ethanol production from Agave salmiana leaf juices by consolidated bioprocessing comparing two strains of Kluyveromyces marxianus

Abstract

The present work addressed the conversion of Agave salmiana leaf juice to ethanol by consolidated bioprocessing (CBP). CBP was tested at 30, 35, and 40 ºC and compared with a conventional fermentation previously subjecting the juices to an acid-thermal pretreatment. An FTIR-DRIFTS analysis was applied on the functional groups of the juice. Fermentation was evaluated by comparing the strains K. marxianus OFF1 and K. marxianus TX4; the latter was isolated in this work from the sap of A. salmiana. In results, the optimal condition pretreatment (H2SO4 0.65% (v/v), 15.7 min, 88 °C) increased the reducing sugars concentration up to 45.15 g/L. FTIR-DRIFTS showed higher peaks of functional groups related to fructose and glucose in the pretreated juice vs the raw. Both strains reached enzymatic activities of up to 2.26 U/mL growing in raw A. salmiana juice. Conventional fermentation showed a similar behavior with both strains, with reducing sugar consumption efficiencies of 98%, 16 g ethanol/L, corresponding to yields of 77%. CBP at different temperatures, showed significant differences, registering the highest ethanol production (22 g/L) and yield (99%) at 40 ºC. The native strain showed a fermentation behavior similar to that of K. marxianus OFF1. Theoretical annual ethanol yields obtained from the results (3828 L/ha/year) were compared to those obtained from other biomass juices such as sweet sorghum and sugarcane bagasse. CBP showed high efficiency in the hydrolysis of polysaccharides from Agave salmiana juice and their conversion to ethanol.