Assessment of granular starch hydrolysis enzyme on ethanol yield from partially swollen sorghum starch and analysis of extracted protein properties

Authors: WEISS, THOMAS - Kansas State University; HONG, SHAN - Kansas State University; XIAO, RUOSHI - Kansas State University; Wu, Xiaorong; LI, YONGHUI - Kansas State University; Tilley, Michael; WANG, DONGHAI - Kansas State University

Submitted to: Journal of Agriculture and Food Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/27/2024
Publication Date: 3/3/2025
Citation: Weiss, T., Hong, S., Xiao, R., Wu, X., Li, Y., Tilley, M., Wang, D. 2025. Assessment of granular starch hydrolysis enzyme on ethanol yield from partially swollen sorghum starch and analysis of extracted protein properties. Journal of Agriculture and Food Sciences. https://doi.org/10.1016/j.jafr.2024.101621.
DOI: https://doi.org/10.1016/j.jafr.2024.101621

Interpretive Summary: Conventional bioethanol production from starch-based crops involves high-temperature cooking, an energy-intensive process that degrades the protein quality of distiller's grains (DG), a valuable co-product. This study investigated the impact of sorghum variety, partial starch swelling treatments, and the use of granular starch hydrolyzing enzyme (GSHE) on ethanol yield and properties of protein extracted from distiller's grains. Results showed that optimal starch swelling conditions (70°C for 30 min) improved the ethanol yield without compromising protein quality in wet distiller’s grains in terms of in vitro protein digestibility. Overall, this research highlights the potential of optimized starch swelling conditions to improve ethanol yield and retain the quality of protein in distiller’s grains, which presents a viable approach for enhancing the sustainability and efficiency of bioethanol production.

Technical Abstract: Conventional bioethanol production from starch-based crops involves high-temperature cooking, which is energy-intensive and degrades the protein quality of distiller's grains (DG), a valuable co-product. This study addresses the critical gap of reducing the energy demand and protein degradation by comparing conventional high-temperature processing with granular starch hydrolyzing enzyme (GSHE) fermentation at low temperatures. Specifically, the novelty lies in optimizing partial starch swelling treatments (50 °C, 60 °C, 70 °C) to enhance ethanol yields while preserving DG protein quality. Using sorghum varieties (normal and waxy) as a model system, we conducted experiments combining low-temperature starch swelling and GSHE fermentation to evaluate their impacts on ethanol yield and protein properties. Waxy sorghum exhibited higher ethanol fermentation efficiency than normal sorghum. Partial starch swelling significantly improved ethanol yield without compromising DG protein quality. GSHE fermentation with starch swelling at 70 °C for 30 min achieved the highest ethanol concentration (12.02 % v/v) and yield (92.74 %) for waxy sorghum. Protein digestibility remained high for both waxy (85.39 %) and normal sorghum (85.21 %) even at higher swelling temperatures. Surface hydrophobicity of DG proteins increased with temperature, particularly at 95 °C during conventional processing. Notably, partial starch swelling improved the lightness (L* values) of sorghum proteins, indicating better quality. Molecular characterization further revealed the specific effects of processing on protein properties. This research highlights the potential of low-temperature starch swelling combined with GSHE fermentation to enhance ethanol production efficiency and protein quality in DG, offering a sustainable alternative to conventional bioethanol processes.