Concerns about decreasing fossil fuel reserves and severe environment concerns encourage the development of renewable alternative raw materials for fuels. Our overall objective is to convert cellulose from pretreated biomass directly to biodiesel, using cellulose-coated emulsion particles as micro-reactors for a cascade of biochemical reactions in a “one-pot” consolidated process. Integration of cellulose-coated o/w emulsion particles with yeast (S. cerevisiae) cells exposes a unique self-assembly configuration. Fluorescence microscope imaging and cryo-SEM imaging provide evidence of an innovative structure of yeast cell connected to surrounding cellulose-coated micro-particles. As proof-of-concept for the first crucial step, this integrated structure is used for simultaneous cellulose saccharification and fermentation to ethanol. GC measurements exhibit ethanol yield of 60% of the theoretical yield. A further proof-of-concept demonstrates the ability of lipase (TLL), integrated in an inner interface within the micro-particles, between the oil core and an inner shell of aqueous cellulose gel, to catalyze transesterification of encapsulated castor oil with ethanol dissolved in the aqueous medium. The activity of lipase-catalyzed transesterification of castor oil to fatty-acid ethanol ester (FAEE) is studied by ¹H NMR to quantify FAEE synthesis at different oil to ethanol ratio, lipase concentration and temperature. Encapsulation of both substrate and enzyme within the same particle allows trans-esterification to be favored over hydrolysis, despite the abundance of water. The results of this study are expected to provide the complete transformation of cellulose to biodiesel by enzymatic hydrolysis, yeast fermentation and lipase-catalyzed transesterification, in a single emulsion-based consolidated bioprocess.

$Cryo-SEM image of the fractured surface of vitrified emulsion containing cellulose-coated castor oil droplets (1:6 cellulose:oil wt. ratio, black arrows) integrated with yeast (<i>S. cerevisiae</i>).$

Cryo-SEM image of the fractured surface of vitrified emulsion containing cellulose-coated castor oil droplets (1:6 cellulose:oil wt. ratio, black arrows) integrated with yeast (S. cerevisiae).

Dmitry Rein

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