ARS | Publication request: Ethanol production performance of ozone treated tannin grain sorghum flour

Submitted to: Cereal Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 13, 2011
Publication Date: January 1, 2012
Citation: Yan, S., Wu, X., Faubion, J., Bean, S., Cai, L., Shi, Y., Sun, X., Wang, D. 2012. Ethanol-production performance of ozone-treated tannin grain sorghum flour. Cereal Chemistry. 89(1):30-37.

Interpretive Summary: In 2009, more than 30% of the U.S. grain sorghum crop was used for ethanol production. Virtually all of the current commercial sorghum lines in the U.S. are tannin-free, and as such little research has been conducted on ethanol production from these sorghum types. Interest in tannin sorghum utilization has increased recently as health benefits associated with tannins have been discovered. Tannin grain sorghum lines also have some agronomic benefits relative to non-tannin sorghums. However, tannin sorghum and its use for ethanol production is not desirable largely because of the adverse effects of the tannins. We tested the effect of ozone on tannin sorghum lines to overcome these negative effects. Ozonation not only decreased measured tannin levels, but also affected properties of sorghum flour and starch. Fermentation efficiency is an important parameter in evaluating the performance of a material for ethanol production, and ethanol fermentation efficiency from ozone-treated sorghum increased over 10% compared to controls. This indicates that ozonation has great impact on ethanol yield and fermentation efficiency and is an effective way to increase ethanol yield and shorten the fermentation process without decreasing ethanol yield.

Technical Abstract: Grain sorghum lines containing tannins have been reported to exhibit increased resistance to drought, birds, mold, preharvest germination, and higher grain yield than non-tannin grain sorghum lines, but tannins have been considered an adverse factor in the utilization of sorghum as a feedstock for bio-ethanol production. Ozone is a strong oxidant and is capable of degrading macromolecules such as lignins. Thus, we hypothesized that ozone treatment may also reduce tannin activity and increase fermentation efficiency of tannin sorghum lines. The objective of this research was to study the physicochemical properties of ozone-treated whole tannin grain sorghum flour and its fermentation performance in ethanol production. Results showed that the ethanol yields from ozone-treated tannin grain sorghums were significantly higher than yields from the untreated flour. The fermentation efficiency of ozone-treated tannin grain sorghum was approximately 90%, which was 8-14% higher than that of untreated samples at the 36th hr of fermentation. At the end of 72 hr of fermentation, the efficiencies of ozone-treated sorghum flour were 2-5% higher than those of untreated samples. Measured tannin levels of ozone-treated samples decreased significantly from 3.8% to 2.7%. Gel permeation chromatography indicated that starch in ozone-treated flours was degraded. Rapid visco analyzer data show that the setback of viscosity of ozone-treated flour was lower than that of untreated flours. Therefore, ozonation could be a novel and useful method to improve ethanol yield and fermentation efficiency of tannin grain sorghum.