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.

[1]  A. Chandrashekar,et al.  Effects of cooking and treatment with sodium bisulfite on in vitro protein digestibility and microstructure of sorghum flour , 1992 .

[2]  Donghai Wang,et al.  Effects of amylose, corn protein, and corn fiber contents on production of ethanol from starch-rich media. , 2006 .

[3]  B. Larkins,et al.  Efficient procedure for extracting maize and sorghum kernel proteins reveals higher prolamin contents than the conventional method , 1995 .

[4]  G. Graham,et al.  Protein quality and digestibility of sorghum in preschool children: balance studies and plasma free amino acids. , 1981, The Journal of nutrition.

[5]  L. Lee,et al.  Relationship Between Rheological Properties and Microstructural Characteristics of Nondeveloped, Partially Developed, and Developed Doughs , 2001 .

[6]  D. Berry,et al.  Physiology of yeast growth , 1987 .

[7]  H. Singh,et al.  Interaction Between Sorghum Protein Extraction and Precipitation Conditions on Yield, Purity, and Composition of Purified Protein Fractions , 2006 .

[8]  E. Mertz,et al.  Pepsin digestibility of proteins in sorghum and other major cereals. , 1984, Proceedings of the National Academy of Sciences of the United States of America.

[9]  Ronald L. Madl,et al.  Factors impacting ethanol production from grain sorghum in the dry-grind process. , 2007 .

[10]  P. Belton,et al.  Factors affecting sorghum protein digestibility , 2003 .

[11]  S. Bean,et al.  Acetonitrile as a buffer additive for free zone capillary electrophoresis separation and characterization of maize (Zeamays L. ) and sorghum (Sorghum bicolor L. Moench) storage proteins. , 2000, Journal of agricultural and food chemistry.

[12]  A. Chandrashekar,et al.  Influence of protein on starch gelatinization in sorghum. , 1988 .

[13]  B. Hamaker,et al.  Resistance of Sorghum .alpha.-, .beta.-, and .gamma.-Kafirins to Pepsin Digestion , 1995 .

[14]  B. Hamaker,et al.  Improving the in vitro protein digestibility of sorghum with reducing agents. , 1987, Proceedings of the National Academy of Sciences of the United States of America.

[15]  B. Hamaker,et al.  Effect of extrusion on sorghum kafirin solubility , 1994 .

[16]  I. Delgadillo,et al.  Effect of Grain Structure and Cooking on Sorghum and Maize in vitro Protein Digestibility , 2002 .

[17]  Donghai Wang,et al.  Effect of Decortication of Sorghum on Ethanol Production and Composition of DDGS , 2005 .

[18]  L. Rooney,et al.  Factors affecting starch digestibility with special emphasis on sorghum and corn. , 1986, Journal of animal science.

[19]  A. Curioni,et al.  Characterisation of Sorghum Kafirins in Relation to their Cross-linking Behaviour , 1998 .

[20]  B. Hamaker,et al.  In vitro protein digestibility of developing and mature sorghum grain in relation to α-, β-, and γ-kafirin disulfide crosslinking , 1995 .

[21]  B. Hamaker,et al.  Low α-amylase starch digestibility of cooked sorghum flours and the effect of protein , 1998 .

[22]  S. Bean,et al.  Investigation and optimization of the factors influencing sorghum protein extraction. , 2003, Journal of agricultural and food chemistry.

[23]  S. Bean,et al.  Faster capillary electrophoresis separation of wheat proteins through modifications to buffer composition and sample handling , 1998, Electrophoresis.

[24]  Andrew D. Jones,et al.  Supporting Online Material for: Ethanol Can Contribute To Energy and Environmental Goals , 2006 .