Comparative evaluation of physicochemical and fermentative responses of three sorghum varieties from dryland and irrigated land and properties of proteins from distillers’ grains

Authors: ZHAO, JIKAI - Kansas State University; WEISS, THOMAS - Kansas State University; DU, ZHENJIAO - Kansas State University; HONG, SHAN - Kansas State University; Bean, Scott; LI, YONGHUI - Kansas State University; WANG, DONGHAI - Kansas State University

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Review Article
Publication Acceptance Date: 1/26/2022
Publication Date: 1/29/2022
Citation: Zhao, J., Weiss, T., Du, Z., Hong, S., Bean, S.R., Li, Y., Wang, D. 2022. Comparative evaluation of physicochemical and fermentative responses of three sorghum varieties from dryland and irrigated land and properties of proteins from distillers’ grains. Journal of Agricultural and Food Chemistry. 104. Article 103432. https://doi.org/10.1016/j.jcs.2022.103432.
DOI: https://doi.org/10.1016/j.jcs.2022.103432

Interpretive Summary: Grain sorghum is a versatile, starch-rich, and drought-resistant crop and is primarily grown in semiarid and arid regions. Although sorghum has a comparable chemical composition to corn, it is often recognized as an underutilized ethanol feedstock. The compositional profile (starch, proteins, free amino nitrogen, and tannin) of sorghum is an important factor related to ethanol fermentation quality. Therefore, the objective of this research was to provide data on chemical composition and fermentation quality of sorghum varieties with different traits grown under dryland and irrigated conditions. The sorghum grown under dryland conditions displayed higher ethanol yield than that grown under irrigation, despite having slightly higher total protein and reduced total starch content. Composition of the residue left after fermentation was influenced by both sorghum variety and irrigation treatment. Thus the conditions that sorghum is grown under (irrigated or non-irrigated) influenced the production of ethanol, while both the variety and growing conditions influenced the composition of the fermentation residue. Growing conditions and sorghum variety need to be considered when breeding and selecting sorghum for the ethanol industry.

Technical Abstract: Three sorghum varieties [waxy sorghum (WS), high protein sorghum (HPS), and normal sorghum (NS)] from dryland and irrigated land were evaluated for physicochemical properties and ethanol fermentation performance. The kafirin proteins were extracted from distillers’ grains with solubles and characterized in terms of purity, digestibility, banding patterns, and molecular size distribution. Starch, crude protein, crude fat, and fiber contents of the sorghums ranged from 64.16 to 68.05%, 11.49 to 13.54%, 2.45 to 2.98%, and 1.62 to1.80%, respectively. For the same variety, the sorghum from dryland had higher protein content (0.33-0.91%) and lower starch content (0.74-1.72%) compared with those from irrigated land. The highest ethanol concentration (85.15 g/L) and yield (87.28%) were obtained in the NS from dryland. Sorghum from dryland displayed 0.94-2.88% of ethanol yield higher than those from irrigated land. Protein (40.21-45.13%), crude fat (11.54 to 13.95%), and crude fiber (7.13-9.29%) content in distillers’ grains with solubles were significantly increased compared to the raw sorghum flour. Although proteins derived from different sorghum sources presented comparable banding patterns, their purity and digestibility ranged from 88.82 to 94.22% and 33.35 to 37.29%, respectively. All the proteins showed a major peak around 670 kDa marker from size-exclusion chromatography. In addition, the effects of sorghum variety, treatment (dryland and irrigated land), and their interaction on the chemical composition of sorghum and distillers’ grains with solubles, ethanol concentration and yield, as well as protein purity and digestibility were elucidated with a set of correlation coefficients among parameters associated with sorghum.