Structural characterization of intermediate wheatgrass (Thinopyrum intermedium) starch

Abstract

Background and objectives:Intermediate wheatgrass (Thinopyrum intermedium, IWG), a perennial, is currently being developed into a food crop that can be used in mainstream food systems. This study focused on characterizing starches extracted from IWG kernels harvested in Roseau (IWG-RS) and Rosemount (IWG-RM) in Minnesota, USA, and compared with starches from Jasmine rice (JR) and hard red wheat (HRW). Thermal properties, size distribution, granule size and morphology, and the unit and internal chain profile of extracted starches were evaluated. Findings: 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 λ max 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 β-limit dextrin and longer external chain. Unit and internal chain profiles of amylopectins between IWGs were similar. Conclusions: This study revealed that the properties of IWG starches were similar to those of wheat. Differences in some starch properties were also observed between the IWG grown at different locations. Significance and novelty: This is the first report on the unit and internal chain profile of IWG. Understanding the microstructure of starch from IWG can potentially optimize its chemical functionality. K E Y W O R D S intermediate wheatgrass, starch, starch gelatinization, unit and internal chain profile 928 | ZHONG et al.

Progress on breeding and food processing efforts to improve chemical composition and functionality of intermediate wheatgrass (Thinopyrum intermedium) for the food industry

“…Therefore, in this review, the term Cycle 1 (C1) refers to the UMN Cycle 1. (d) Cycle 2 IWG (C2)—these are varieties from the second cycle of the TLI breeding program harvested in 2015 at two locations in Minnesota (MN), Roseau, and Rosemount, (Banjade et al., 2019; Banjade et al., 2019; Mathiowetz, 2018; Zhong et al., 2019). Hayek (2020) and Luu (2020) also analyzed Cycle 2 IWG (C2) samples harvested in 2016 in Roseau, MN (Hayek, 2020; Luu, 2020).…”

“…Zhong et al. (2019a, 2019b) studied starch hydrolysis kinetics of IWG starch and flour from C2, harvested at two growing locations, and evaluated the structural characteristics of IWG starches and compared it to more commonly consumed cereals such as jasmine rice and HRW. In vitro studies on starch digestibility kinetics mimic the breakdown of starch into glucose by human digestive enzymes and classify starches into three categories: rapidly digestible starch corresponding to starch hydrolyzed within 20 min after consumption; slowly digestible starch, the amount of starch hydrolyzed between 20 and 120 min after consumption; resistant starch (RS) constituting starch not hydrolyzed after 2 hr.…”

“…With an increase in seed size, it is expected that there will be an increase in starch content, but a decrease in grain protein due to the natural trade‐off a plant makes in resource allocation (Lopez & Grabe, 1973). Starch content and pasting properties have been reported for bulk IWG (Marti et al., 2015), C1 (Rahardjo et al., 2018), IWG variety MN1503 which is part of UMN’s C1 and harvested in Becker, MN (Tyl et al., 2019), C2 (Banjade, Gajadeera, et al., 2019; Banjade, Tyl, et al., 2019; Hayek, 2020; Luu, 2020; Mathiowetz, 2018; Tyl & Ismail, 2019; Zhong et al., 2019), C3 (Tyl & Ismail, 2019), and C5 (Hayek, 2020; Luu, 2020). Table 2 lists starch contents for different IWG cycles.…”

“…Both IWG flours had significantly lower HI than HRW and jasmine rice flours. The gelatinization temperature of starches from the two IWG flours from different growing locations was relatively lower HRW and jasmine rice starches; however, the range of gelatinization among these starches was comparatively uniform (Zhong et al., 2019b). While none of the cooked flour samples differed in their slowly digestible starch contents, both IWG flours contained less rapidly digestible starch than jasmine rice flour.…”

“…IWG RS had significantly shorter average chain length than HRW, in line with Scanning Electron Microscopy results showing that its RS fractions experienced more hydrolysis than HRW RS. HRW RS had the lowest molar ratio of short to long chains and thus possessed the highest mole percent of long chains and lowest amount of glucose after debranching (Zhong et al., 2019).…”