Renyong Zhao

Factors impacting ethanol production from grain sorghum in the dry-grind process.

ABSTRACT The goal of this research is to understand the key factors affecting ethanol production from grain sorghum. Seventy genotypes and elite hybrids with a range of chemical compositions and physical properties selected from ≈1,200 sorghum lines were evaluated for ethanol production and were used to study the relationships of composition, grain structure, and physical features that affect ethanol yield and fermentation efficiency. Variations of 22% in ethanol yield and 9% in fermentation efficiency were observed among the 70 sorghum samples. Genotypes with high and low conversion efficiencies were associated with attributes that may be manipulated to improve fermentation efficiency. Major characteristics of the elite sorghum genotypes for ethanol production by the dry-grind method include high starch content, rapid liquefaction, low viscosity during liquefaction, high fermentation speed, and high fermentation efficiency. Major factors adversely affecting the bioconversion process are tannin content, l...

Effects of amylose, corn protein, and corn fiber contents on production of ethanol from starch-rich media.

ABSTRACT The effects of amylose, protein, and fiber contents on ethanol yields were evaluated using artificially formulated media made from commercial corn starches with different contents of amylose, corn protein, and corn fiber, as well as media made from different cereal sources including corn, sorghum, and wheat with different amylose contents. Second-order response-surface regression models were used to study the effects and interactions of amylose, protein, and fiber contents on ethanol yield and conversion efficiency. The results showed that the amylose content of starches had a significant (P 35%. The reduced quadratic model fits the conversion efficiency data better than the full quadratic mode...

Effects of growing location and irrigation on attributes and ethanol yields of selected grain sorghums.

ABSTRACT Nine sorghum cultivars (five inbred lines and four hybrids) were grown in 2006 in three locations (Mount Hope, KS, Halstead, KS, and Plainview, TX) under different irrigation conditions and were evaluated for composition and ethanol fermentation efficiency. The objective was to study, in one growing season, the effects of genotype, growing location, and irrigation on the physical and chemical properties and fermentation efficiencies of grain sorghum. Genotype had a significant effect on chemical composition, physical properties, and ethanol yield. The cultivars showed a large variation in starch (61.0–74.8%), protein (7.56–16.35%), crude fat (2.79–4.77%), crude fiber (0.58–2.57%), ash (1.25–2.26%), kernel weight (20.0–35.9 mg), kernel hardness (49.6–97.5), and kernel size (1.9–2.7 mm) and were the most important factors affecting ethanol fermentation efficiency (87.5–93.9%). Starch and protein contents were significantly affected by growing location but not by irrigation. Environment had a signif...

Impact of mashing on sorghum proteins and its relationship to ethanol fermentation.

Nine grain sorghum cultivars with a broad range of ethanol fermentation efficiencies were selected to characterize the changes in sorghum protein in digestibility, solubility, and microstructure during mashing and to relate those changes to ethanol fermentation quality of sorghum. Mashing reduced in vitro protein digestibility considerably, and a large amount of polymers cross-linked by disulfide bonds were developed during mashing. As a marker of cross-linking, protein digestibility of the original samples was highly related to conversion efficiency. gamma-Kafirin (%) neither correlated to ethanol yield nor conversion efficiency significantly. Solubility of proteins in an alkaline borate buffer in conjunction with SDS decreased substantially after mashing. Solubility and the SE-HPLC area of proteins extracted from mashed samples were highly correlated with ethanol fermentation. Ethanol yield increased and conversion efficiency improved notably with the increase of extracted proteins from mashed samples. SE-HPLC total area could be used as an indicator to predict ethanol fermentation. CFLSM images proved that sorghum proteins tended to form highly extended, strong web-like microstructures during mashing. The degree of protein cross-linking differed among samples, and more open microstructures were observed in samples with higher conversion efficiencies. The web-like protein matrix was found to hold not only starch granules but also some oligosaccharides or polysaccharides inside. The formation of web-like microstructures because of cross-linking reduced conversion efficiency.

Comparison of Waxy vs. Nonwaxy Wheats in Fuel Ethanol Fermentation

ABSTRACT Fermentation performance of eight waxy, seven nonwaxy soft, and 15 nonwaxy hard wheat cultivars was compared in a laboratory dry-grind procedure. With nitrogen supplements in the mash, the range of ethanol yields was 368–447 L/ton. Nonwaxy soft wheat had an average ethanol yield of 433 L/ton, higher than nonwaxy hard and waxy wheat. Conversion efficiencies were 91.3–96.2%. Despite having higher levels of free sugars in grain, waxy wheat had higher conversion efficiency than nonwaxy wheat. Although there was huge variation in the protein content between nonwaxy hard and soft wheat, no difference in conversion efficiency was observed. Waxy cultivars had extremely low peak viscosity during liquefaction. Novel mashing properties of waxy cultivars were related to unique pasting properties of starch granules. With nitrogen supplementation, waxy wheat had a faster fermentation rate than nonwaxy wheat. Fermentation rates for waxy cultivars without nitrogen supplementation and nonwaxy cultivars with nitro...

Assessing Fermentation Quality of Grain Sorghum for Fuel Ethanol Production Using Rapid Visco Analyzer

ABSTRACT The Rapid Visco-Analyzer (RVA) was used to characterize the pasting properties of 68 sorghum grains with a standard 23-min temperature profile. The results showed a strong linear relationship between ethanol yield and final viscosity as well as setback. Ethanol yield increased as final viscosity decreased. A modified RVA procedure (10 min) with an application of α-amylase was developed to simulate the liquefaction step in dry-grind ethanol production. There was a remarkable difference in mashing properties among the sorghum samples with the normal dosage of α-amylase. The sorghum samples which were difficult to liquefy in the mashing step had much higher peak viscosities than the samples that were easily liquefied. The results also showed that the relationship between conversion efficiency and mashing property was significant. Tannins cause high mash viscosities. There was a strong linear relationship between tannin content and final viscosity as well as peak viscosity. The modified RVA procedure...

Sorghum Protein Extraction by Sonication and Its Relationship to Ethanol Fermentation

Cereal Chem. 85(6):837–842 The objectives of this research were to develop a rapid method for extracting proteins from mashed and nonmashed sorghum meal using sonication (ultrasound), and to determine the relationships between the levels of extractable proteins and ethanol fermentation properties. Nine grain sorghum hybrids with a broad range of ethanol fermentation efficiencies were used. Proteins were extracted in an alkaline borate buffer using sonication and characterized and quantified by size-exclusion HPLC. A 30-sec sonication treatment extracted a lower level of proteins from nonmashed sorghum meal than extracting the proteins for 24 hr with buffer only (no sonication). However, more protein was extracted by sonication from the mashed samples than from the buffer-only 24-hr extraction. In addition, sonication extracted more polymeric proteins from both the mashed and nonmashed samples compared with the buffer-only extraction method. Confocal laser-scanning microscopy images showed that the web-like protein microstructures were disrupted during sonication. The results showed that there were strong relationships between extractable proteins and fermentation parameters. Ethanol yield increased and conversion efficiency improved significantly as the amount of extractable proteins from sonication of mashed samples increased. The absolute amount of polymeric proteins extracted through sonication were also highly related to ethanol fermentation. Thus, the SE-HPLC area of proteins extracted from mashed sorghum using sonication could be used as an indicator for predicting fermentation quality of sorghum. Sorghum (Sorghum bicolor L. Moench) is a drought-resistant and low-input cereal grain grown throughout the world, and interest in using it for bioindustrial applications is now growing in the United States (Farrell et al 2006). Although currently only ≈2.5% of fuel ethanol is produced from grain sorghum, annual consumption of sorghum by the ethanol industry is steadily increasing from 11.25% in 2004 to 15% in 2005 and 26% in 2006 (Renewable Fuels Association 2005, 2006, 2007). Researchers and ethanol producers have shown that grain sorghum is a viable feedstock (technically acceptable, fits the infrastructure, and can be economically viable) for ethanol, and could make a larger contribution to the nation’s fuel ethanol requirements. Starch and protein are the two major components in sorghum grain. Recent research has shown that starch content is a good indicator of ethanol yield in the dry-grind process but starch content itself could not explain conversion efficiency well (Wu et al 2007). Sorghum varies in protein content from 6 to 18%, with 70–90% of the total protein belonging to the storage proteins (kafirins) (Lookhart et al 2000). According to previous research with 68 sorghum hybrids, a strong negative correlation was observed between ethanol yield and protein content (R 2 = 0.60, P < 0.01) (unpublished data), which is similar to data reported for soft wheat cultivars (Swanston et al 2007). However, multiple linear regression, including both starch and protein content as predictors, verified that protein content did not significantly contribute to ethanol yield (P = 0.395). The effect of protein content on conversion efficiency was statistically significant (P = 0.015) but represented only 8.6% of variation in efficiency (unpublished data).

The impacts of protein on grain sorghum ethanol fermentation efficiency

Nine grain sorghum samples with a broad range of ethanol fermentation efficiencies (EFE) were used for this study. Relationships between free amino nitrogen (FAN), protein digestibility, protein extractability, and protein microstructure to EFE were investigated. Only 0.60%~1.20% of sorghum protein was liberated in the form of free amino acids during mashing and this amount of FAN was not enough to support yeast fermentation. Protein digestibility reduced significantly during mashing. No strong linear relationship between protein digestibility and EFE was observed after mashing. However, there was a strong linear relationship between EFE and the amount of extractable protein from mashes. The extractable protein could be used for prediction of EFE. The proteins extracted with sonication induced by 2% s-mercaptoethanol and separated by SEC showed that the extractable non-disulphide cross-linked oligomers were positively related to EFE. Confocal laser scanning was used to analyze the effect of mashing on protein structure. The images showed that sorghum proteins tended to form highly extended, strong web-like microstructures during mashing. The degree of protein cross-linking was different among samples. The formation of web-like microstructures due to cross-linking reduced EFE.

Factors Adversely Affecting Ethanol Production in the Dry Grind Processing of Sorghum

Many factors may contribute to the low ethanol yield and fermentation efficiency of sorghum varieties. The effects of particle size of ground sample, viscosity, enzyme-resistant starches, and protein matrix on ethanol fermentation have been investigated. Finely ground samples could yield as much as 5% more ethanol than coarsely ground samples. Samples with a dense protein matrix around starch granules had low ethanol yield and fermentation efficiency; steeping with sodium bisulfate or treating with protease both improved ethanol fermentation efficiency by up to 2.5-3.0%. The significantly reduced residual starch content in the DDG of the treated samples further confirmed the effects of steeping and protease treatment. A starch-rich fraction that escaped enzyme hydrolysis during mashing was separated from the mashed residues of a low efficient sample. The amount of this fraction accounted for approximately 2.5% of the total starch. DSC thermogram showed three distinct endothermic peaks at 98 °C, 110 °C, and 142 °C. More studies to characterize the chemical and physical properties of this fraction are in progress. The fermentation efficiency of low-ethanol yielding sorghums could reach levels comparable to those of corn when appropriate integrated strategies are applied.

Ethanol Production as Affected by Sorghum Chemical Composition, Chemical Structure and Physical Properties

The objective of this research was to understand the relationship among “geneticsstructure- function-conversion” and the key factors impacting ethanol production from sorghum. Seventy sorghum genotypes and elite hybrids with broad range of chemical compositions and physical properties from 1200 sorghum lines have been evaluated for ethanol production and used to study the relationship among composition, chemical structure, physical features, and available/ usable starch on ethanol fermentation efficiency. Genotype had a significant effect on final ethanol yield and fermentation efficiency. Variations of 22% in ethanol yield and 9.1% in fermentation efficiency were observed among the 70 sorghum samples. Genotypes with extremely high and low conversion efficiencies and some specific attributes that may be manipulated to improve the bioconversion rate of sorghum were identified. Major characteristics of the elite sorghum genotypes for the bioconversion process include high starch content (high yields), quick liquefaction, low viscosity during liquefaction, high fermentation speed, and high bioconversion efficiency. Major factors adversely affecting the bioconversion efficiency of grain sorghum are phenol compounds, tight-storage protein matrix, low-protein digestibility, high viscosity, and high-gelatinization temperature (amylose-lipid complexes).