Amylose content of sorghum starches as measured by four different methods in relation to molecular structures of sorghum amylose and amylopectin

Authors: LI, DONGXING - Kansas State University; Wu, Xiaorong; Bean, Scott; SHI, YONG-CHENG - Kansas State University

Submitted to: Carbohydrate Polymers
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/23/2025
Publication Date: 11/29/2025
Citation: Li, D., Wu, X., Bean, S.R., Shi, Y. 2025. Amylose content of sorghum starches as measured by four different methods in relation to molecular structures of sorghum amylose and amylopectin. Carbohydrate Polymers. https://doi.org/10.1016/j.carbpol.2025.124741.
DOI: https://doi.org/10.1016/j.carbpol.2025.124741

Interpretive Summary: Amylose content significantly affects functional quality and nutritional properties of a starch or cereal grain, yet different measuring methods often give different values for the same cereal or starch sample. The objectives of this study were to compare the amylose measuring methods and understand possible causes for the differences among the methods. A colorimetric method (starch-iodine complex based), differential scanning colorimetry (DSC) based method, a commonly used commercial method (Concanavalin A: Con A based), and gel permeation chromatography (GPC) method were compared. The amylose measurements obtained from the GPC procedure were ~ 1–2% higher than those from the iodine-complexing based colorimetric method and the DSC method. The commercial procedure underestimated the amylose content by about 7% compared with the other methods, possibly due to how chemicals in the commercial method interacted with the starch components during measurement. These results will benefit researchers studying starch composition and the cereal and grain industry by demonstrating how different methods can impact measurement of starch composition, knowledge which is important for understanding product quality, functionality and specifications.

Technical Abstract: Amylose content plays important roles in functional and nutritional properties of a starch, yet different amylose contents are often obtained by different methods even for the same cereal or starch sample. Thus, the objectives of this study were to compare the amylose content of sorghum starches and flours measured by four different methods and understand the differences between the methods. The amylose contents of diverse sorghum flours measured by a colorimetric method based on starch-iodine complex and amylose measured using differential scanning colorimetry (DSC) method based on the enthalpy change of starch-lipid complex showed highly repeatable results. The results from these two methods were also close with the amylose contents of the respective starches measured by gel permeation chromatography (GPC) method. A reliable and feasible method for isolating amylose/amylopectin of sorghum starches was developed based on the binding capacity of starch molecules with 1-butanol/iso-amyl alcohol. According to the structures of the isolated amylose/amylopectin, the true amylose contents were calculated and where ~ 1–2% higher than the results obtained from by colorimetric and DSC methods. The small differences reflected the sufficient accuracy of those two measurements. Comparing to the DSC method, the colorimetric method is more time efficient. Amylose/amylopectin of sorghum starches were also isolated with Concanavalin A (Con A). By comparing the molecular size distributions of amylose/amylopectin fractionated by 1-butanol/iso-amyl alcohol and amylose/amylopectin separated from Con A, we estimated that ~ 7% of amylose fractions was precipitated out in the amylopectin fraction in the Con A method, resulting in significantly lower amylose content of sorghum starches/flours compared to the results from the other methods. The Con A method measures linear and less branched amylose in sorghum starch.