Ethanol Production Performance of Ozone Treated Tannin Grain
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e-Xtra* Ethanol-Production Performance of Ozone-Treated Tannin Grain Sorghum Flour1 Shuping Yan,2,3 Xiaorong Wu,2 Jon Faubion,4 Scott R. Bean,5 Liming Cai,4 Yong-Cheng Shi,4 Xiuzhi S. Sun,4 and Donghai Wang2,6 ABSTRACT Cereal Chem. 89(1):30–37 Ozone has been reported as being able to degrade macromolecules 72 hr of fermentation, the efficiencies of ozone-treated sorghum flour such as cellulose, starch, lignins, and tannins in the textile, pulping, were 2–5% higher than those of untreated samples. Measured tannin and water-treatment industries. Thus, we hypothesized that ozone treat- levels of ozone-treated samples decreased significantly from 3.8 to ment may also inactivate tannin activity and increase fermentation ef- 2.7%. Gel-permeation chromatographic results indicated that both deg- ficiency of tannin sorghum lines. The objective of this research was to radation and polymerization processes might have happened to starch study the physicochemical properties of ozone-treated whole tannin molecules during ozone treatment. Rapid Visco Analyzer data showed grain sorghum flour and its fermentation performance in ethanol pro- that the setback of viscosity of ozone-treated flour was lower than that duction. Results showed that the ethanol yields from ozone-treated of untreated flours. Distillers dried grains with solubles made from tannin grain sorghums were significantly higher than yields from the ozone-treated sorghum were low in residual starch (<1%) and high in untreated flour. The fermentation efficiency of ozone-treated tannin crude protein (≈35%). Therefore, ozonation could be a novel and use- grain sorghum was approximately 90%, which was 8–14% higher than ful method to improve ethanol yield and fermentation efficiency of that of untreated samples at the 36th hr of fermentation. At the end of tannin grain sorghum. The use of ethanol as a gasoline alternative, ethanol production, sorghum have focused on these grain sorghum types. Little re- and ethanol-production capacity in the United States are increas- search has been conducted on ethanol production from tannin ing rapidly because of federal mandates requiring the mixing of sorghum lines. Interest in tannin sorghum utilization has in- ethanol into gasoline. As stipulated by the Energy Independence creased as health benefits associated with tannins have been dis- and Security Act of 2007 and the expanded Renewable Fuels covered (Awika and Rooney 2004); tannin grain sorghum lines Standard, annual ethanol production will grow to 15 billion also have been shown to carry agronomic benefits such as resis- gallons by 2012 and to 36 billion gallons by 2022. Currently, tance to drought, birds, mold, insects, and disease and higher ethanol in the United States is produced mainly from crop-based grain yield than nontannin grain sorghum (Reichert et al 1980; starch-rich grains. Grain sorghum is one of the primary feed- Hahn and Rooney 1986). Although growing tannin sorghum has stocks for ethanol production. In 2009, more than 30% of the U.S. the advantages of lower production and storage costs and higher grain sorghum crop was used for ethanol production. As a major grain yields, the production of tannin sorghum and its use for sorghum grower, the state of Kansas used approximately 50% of ethanol production and animal feed are not desirable, largely be- its 2010 sorghum crop for ethanol production (Agri-Energy cause of the adverse effects of tannin on enzyme activity, starch Solutions 2009; Jessen 2010). and protein digestion, and ethanol fermentation efficiency. For Grain sorghum is a viable feedstock for ethanol production (D. identity-preserved and specialty markets, however, the use of tan- Wang et al 2008), and the performance of grain sorghum in etha- nin sorghum is very attractive. nol production has been studied and evaluated recently (Monk et Tannins are a group of highly hydroxylated phenolic com- al 1984; Wu et al 2007, 2010). Ethanol conversion efficiency has pounds that are common in plants. Sorghum tannins have been been intensively studied because of the importance of, and public actively studied for some time now with regard to food or feed concern over, net energy gain in ethanol production. Virtually all uses. Tannins may impact the processing, product quality, and of the current commercial sorghum lines in the United States are nutritional values of sorghum (Elkin et al 1996; Awika and tannin-free, and most of the previous research studies involving Rooney 2004; Kobue-Lekalake et al 2009). Sorghum tannins are located in the outer layers of the kernel, beneath the pericarp in the pigmented testa layer of sorghum grain. Tannins protect sor- * The e-Xtra logo stands for “electronic extra” and indicates that Figures 3 and 4 ghum grains, but because of their negative effects in animal nutri- appear in color online. tion, many studies have been conducted to remove or deactivate 1 Contribution number 11-346-J from the Kansas Agricultural Experiment Station, tannins. Chibber et al (1978) reported that mechanical abrasion or Manhattan, KS 66506. decortication of sorghum coat layers could reduce the tannin con- 2 Department of Biological and Agricultural Engineering, Kansas State University, tent of sorghum flour for food uses by physically removing the Manhattan, KS 66506. tannins. Reichert et al (1980) reported that anaerobic storage of 3 Current address: C. W. Brabender Instruments, Inc., 50 East Wesley Street, South Hackensack, NJ 07606. grain sorghum treated with water or HCl solution decreased tan- 4 Department of Grain Science and Industry, Kansas State University, Manhattan, nin content in grain sorghum. Daiber and Taylor (1982) steeped KS 66506. sorghum seeds in dilute formaldehyde solution and dilute NaOH 5 United States Department of Agriculture (USDA), Agricultural Research Service, to decrease tannin levels. These methods likely degraded or cross- Grain and Animal Health Research Center, Manhattan, KS 66502. Names are linked the tannins, rendering them inactive. Germination of grain necessary to report factually on available data; however, USDA neither guarantees nor warrants the standard of the product, and the use of the name by the USDA sorghum is another way to reduce tannin content (Reichert et al implies no approval of the product to the exclusion of others that may also be used. 1980; Yan et al 2009). Deactivation of tannins during germina- 6 Corresponding author. Phone: (785) 532-2919. Fax: (785) 532-5825. E-mail: tion was similar to the reduction reported during anaerobic stor- [email protected] age of water-treated sorghum. The deactivation mechanism in http://dx.doi.org/10.1094/ CCHEM-06-11-0075 both processes may be the same, that is, enzymatic degradation © 2012 AACC International, Inc. (Yan et al 2009). 30 CEREAL CHEMISTRY Mullins and NeSmith (1986) studied ethanol fermentation from pensions were incubated in a 45°C water-bath shaker for 72 hr bird-resistant (i.e., tannin-containing) and non-bird-resistant (i.e., with constant agitation (150 rpm). The content from the flask was containing no tannins) grain sorghum and reported that high tan- sieved through a no. 200 wire sieve (opening 75 μm), and the nin levels greatly reduced the ethanol-production rate. Wu et al retained overs were washed twice with 200 mL (2 × 200 mL) of (2007) reported tannin content as a major factor affecting ethanol distilled water to recover starch. The washed overs were dis- conversion efficiency of grain sorghum in lines containing tan- carded, and the throughs were collected and passed through a no. nins. All results showed that ethanol yield and fermentation effi- 200 wire sieve (opening 75 μm). Again, the overs were discarded ciency increased as tannin content decreased in treated sorghum and the throughs were centrifuged at 3,000 × g for 30 min. After (Yan et al 2009). each centrifugation, the supernatant and tailings were removed Ozone is a strong oxidant with oxidation potential of 2.07 eV. and discarded. The prime starch was washed with distilled water Ozone has the power to degrade vital components in living cells and centrifuged at 3,000 × g for 30 min. A total of 10 washing quickly and to kill microorganisms. It works at low dosage levels and centrifuge cycles were conducted to obtain clean prime and leaves no residue in the treated product. Because of these starch. The prime starch was freeze-dried for gel-permeation advantages, ozone has been used in water treatment, food proc- chromatography. essing (Kim et al 1999), and corn and wheat steeping prior to milling (Ruan et al 2004; Dhillon et al 2009). Previous studies Gel-Permeation Chromatography have shown that ozone degrades macromolecules such as lignin Four milligrams of purified starch from whole-grain sorghum (Sugimoto et al 2009), protein, and carbohydrates (Yosef et al flour was mixed with 4 mL of dimethyl sulfoxide (DMSO) and 1994; Wang et al 1999, 2008). Seo et al (2007) reported that chi- stirred in a boiling water bath for 24 hr. The sample was filtered tosan could be depolymerized by ozone treatment. Thus, the hypo- through a 2 µm filter, and then 200 µL was injected into a gel- thesis of the current project was that ozone treatment may degrade permeation chromatography (GPC) instrument (PL-GPC 220, or inactivate sorghum tannin and reduce its adverse activity dur- Polymer Laboratories, Amherst, MA) equipped with three differ- ing fermentation, thereby increasing the fermentation efficiency ent pore sizes of Phenogel columns (100Å, 103Å, and 105Å, Phe- of tannin sorghum. A process for deactivating sorghum tannins nogel GPC, 10 µm, 300 × 7.8 mm), a guard column (Phenome- prior to ethanol fermentation would enable additional uses for nex, Torrance, CA), and a differential refractive index detector. tannin-containing sorghum lines grown for special purposes such The eluent system was DMSO containing 5.0 mM NaNO3 at a as nutraceuticals or would prove valuable in areas of the world flow rate of 0.8 mL/min.