Rheological Hardness Index for Assessing Hardness of Hexaploids and Durums

Abstract

Cereal Chem. 90(5):430-438Kernel hardness of cereal grains is a fundamental phenotype, and various protocols for its characterization have been proposed. Although, from different perspectives, each has proved useful, these methods do not directly address the rheological (fracturing) response of a grain when subjected to compression. Such information is hidden in the individual crush response profiles (iCRPs) obtained by measuring the response of individual grains to crushing on an SKCS 4100 device. Here, the appropriateness and utility of rheological phenotypes, based on single-kernel measurements, are demonstrated by proposing and validating a new wheat grain hardness phenotype, the rheological hardness index (RHI). It is defined in terms of the rheological phenotype phases (RPPs) of the averaged CRPs (aCRPs) obtained by averaging a large number of iCRPs. The utility of RHI is illustrated by showing how it provides improved insight about the differences in brittleness and compactness of grains from different wheat varieties. This investigation highlights the opportunity that the RPP of the aCRPs represent for obtaining specific quantitative phenotypes for the study of hardness in cereal grains. In particular, successful plant breeding relies on segregating a breeding population into appropriate end-use categories, for which RHI has a potential role to play.

Using Rheological Phenotype Phases to Predict Rheological Features of Wheat Hardness and Milling Potential of Durum Wheat

“…This overlap suggests that using SKCS HI to classify wheats into separate quality categories, with respect to some chosen rheological property, could lead to nonoptimal breeding outcomes. More energy is required to fragment the shells of the hard wheats and durums compared with soft wheats, and this was also observed in a smaller set of samples (Haraszi et al 2013). The elastic response (SR/SC, where SC is shell collapse) versus RHI scatter plot (Fig.…”

“…There is an initial resistance of the husk during which the force increases, followed by kernel fragmentation, which creates fractures and lowers the resistance. Arbitrary hardness classes are based on RHI following the ranges defined by Haraszi et al (2013) with some modification. The RHIs derived from the aCRPs for each of the varieties and the SKCS HI values are shown in Table I.…”

“…During further crushing, this material presents further resistance (viscoelastic response) until final collapse of the granular kernel, after which the force declines rapidly to zero. It was suggested by Haraszi et al (2013) that the proposed hardness classes based on RHI may be further subcategorized. Arbitrary hardness classes are based on RHI following the ranges defined by Haraszi et al (2013) with some modification.…”

“…Osborne and Anderssen (2003) introduced the concept of rheological phenotype phases (RPPs) to characterize the different rheological features highlighted in an aCRP. Subsequently, Haraszi et al (2013) examined the use of combinations of RPPs (cRPPs) to improve on the characterization of grain hardness and specifically introduced and examined a new cRPP, the rheological hardness index (RHI) (the ratio of the endosperm response [EndoR] divided by the time to endosperm collapse [EndoC]). The utility of these observations was confirmed in a series of papers by Edwards and coworkers (e.g., Edwards et al 2007;Edwards 2010).…”

“…They observed that combinations of those features could be utilized to recover higher level rheological properties such as shell elasticity and illustrated that scatter plots of different RPPs had the potential to separate wheat into different hardness classes (clusters). They established that, compared with using scatter plots of RPPs alone, improved separation of the different wheat hardness classes was achieved with scatter plots in which RHI was the independent variable compared with using SKCS HI (Haraszi et al 2013). Subsequently, Haraszi et al (2013) examined the use of combinations of RPPs (cRPPs) to improve on the characterization of grain hardness and specifically introduced and examined a new cRPP, the rheological hardness index (RHI) (the ratio of the endosperm response [EndoR] divided by the time to endosperm collapse [EndoC]).…”