Structural Characterization and Glycemic Attributes of Intermediate Wheatgrass (Thinopyrum intermedium) Flour and Extracted Starch

Abstract

Intermediate wheatgrass (IWG) is an environmentally sustainable perennial crop with potential food applications. This study investigated the starch hydrolysis kinetics of IWG grown in Roseau (IWG-RS) and Rosemount (IWG-RM), Minnesota, USA and the molecular structure of their residual (resistant) starch after 2 hr hydrolysis. Hard red wheat (HRW) and Jasmine rice (JR) were compared to the IWG samples. Molecular size distribution and unit chain profiles of the RS fraction of raw starches after enzymatic hydrolysis were determined with gel permeation chromatography and high-performance anion-exchange chromatography respectively. Moreover, thermal properties, size distribution, granule size and morphology, as well as the unit and internal chain profile of extracted starches were evaluated. IWG flour had significantly lower total starch, lower RDS and higher lipid and protein contents compared to JR and HRW. JR flour had the highest eGI (49.2), with IWG-RM recording the lowest (40.6). Significant differences were observed in the glucan chain lengths of the RS fraction. JR had the shortest average chain length (DP=4.75) compared to HRW (DP=7.46), IWG-RS (DP=5.72) and IWG-RM (DP=4.85). IWG flour had slower starch hydrolysis kinetics compared to JR and HRW flour. The RS fraction of the samples consisted mostly of short chains. The glucan chain length of IWG RS fraction was also significantly affected by location. The amylose contents of IWG-RS and IWG-RM were 30.7% and 30.4%, respectively. IWG starches had the lowest gelatinization temperatures. Enthalpy of gelatinization (ΔH) of HRW was similar to that of IWG-RM. The λmax of the starches suggests that the amylose chains and internal chains of the IWG starches were longer than those of HRW and JR. IWG-RM has the least beta-limit dextrin and longer external chain. Unit and internal chain profiles of amylopectins between IWGs were similar. This study revealed that IWG could potentially be exploited for the preparation of foods with lower glycemic responses. IWG starches properties were similar to those of wheat. Differences in some starch properties were also observed between the IWG grown at different locations. Understanding the microstructure of starch from Intermediate wheatgrass can potentially optimize its chemical functionality.