ARS | Publication request: Simultaneous saccharification and fermentation of orange processing waste to ethanol using Kluyveromyces marxianus

Submitted to: Biological Engineering (ASABE)
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 28, 2009
Publication Date: November 1, 2009
Citation: Widmer, W.W., Narciso, J.A., Grohmann, K., Wilkins, M.R. 2009. Simultaneous saccharification and fermentation of orange processing waste to ethanol using Kluyveromyces marxianus. Biological Engineering (ASABE). 2(1):17-29.

Interpretive Summary: Citrus processing waste (CPW) from the production of citrus juices is a promising resource for the production of fuel ethanol because it is rich in soluble sugars and polymeric carbohydrates. It contains little lignin content and can be easily hydrolyzed by a mixture of pectinolytic, cellulolytic and hemicellulolytic enzymes to soluble sugars. After removal of limonene, an antimicrobial terpene, the sugars (glucose, fructose and sucrose) in CPW can be fermented to ethanol by yeasts. The performance of the thermotolerant yeast Kluyveromyces marxianus (NRRL Y 1137) was evaluated in the temperature range of 37-450 °C because Saccharomyces cerevisiae, the yeast normally used for ethanol fermentations does not tolerate temperatures above 400 °C. The ability to use an organism for simultaneous saccharification and fermentation (SSF) of CPW at elevated temperatures (40-450 °C) would be advantageous because the enzymes used in saccharification or hydrolysis of CPW work optimally at 450 °C. Our study found the K. marxianus strain tested can efficiently ferment sugars in hydrolyzed CPW in the temperature range of 37-400 °C and at higher (41-450 °C) temperatures with a lower yield. Growth of the K. marxianus on hydrolyzed CPW was stimulated by a higher (4.6-5.2) pH of the medium and by supplementation with ammonium sulfate or yeast extract.

Technical Abstract: Citrus processing waste (CPW) from the production of citrus juices is a promising resource for the production of fuel ethanol. This waste, mainly peel, is rich in soluble sugars and polymeric carbohydrates. It has a very low lignin content and can be easily hydrolyzed by a mixture of pectinolytic, cellulolytic and hemicellulolytic enzymes to soluble sugars. After removal of limonene, an antimicrobial terpene, part of the resulting sugars (glucose, fructose and sucrose) can be fermented to ethanol by yeasts. The performance of the thermotolerant yeast Kluyveromyces marxianus (NRRL Y 1137) has been evaluated in simultaneous saccharification and fermentation (SSF) of deterpenized orange processing waste at elevated temperatures (37-450 °C) and approximate pH range of 4-5. The strain can efficiently ferment sugars in hydrolyzed CPW in the temperature range of 37-400 °C and at higher (41-450 °C) temperatures with a lower yield. Growth of K. marxianus on hydrolyzed CPW is stimulated by a higher (4.6-5.2) pH of the medium and by supplementation with ammonium sulfate or yeast extract.