The Effect of Wheat Moisture and Hardness on the Parameters of the Peleg and Normand Model during Relaxation of Single Kernels at Variable Initial Loading

Abstract

The aim of the study was to examine the Peleg and Normand model to characterize the overall stress relaxation behavior of wheat kernel at varying load conditions. The relaxation experiments were made with the help of the universal testing machine, Zwick Z020, by subjecting the samples to compression at four distinct initial load levels, i.e., 20 N, 30 N, 40 N, and 50 N. The measurements were made for four wheat varieties (two soft and two hard-type endosperms) and seven levels of moisture content. Relaxation characteristics were approximated with the help of the Peleg and Normand equation. An interactive influence of the load level, moisture, and wheat hardness on the Peleg and Normand constants has been confirmed. For moist kernels, a higher amount of absorbed compression energy was released, since less energy was required to keep the deformation at a constant level. The constants differed depending on wheat hardness. Higher values of k 1 revealed that the initial force decay was slower for hard varieties. This is more characteristic of elastic behavior. Similarly, higher values of k 2 pointed to a larger amount of elastic (recoverable) energy at the end of the relaxation. The initial loading level had no or only a slight effect on the model coefficients (Y(t), k 1 , and k 2 ). The parameters of the Peleg and Normand model decreased with an increase in the water content in the kernels.Sustainability 2019, 11, 7100 2 of 18 simply defined, since it changes depending on the farmer, grain dealer, seed company, milling industry, pasta industry, and consumer. For the farmers it can be yield or resistance to disease, for miller's protein content, hardness, or many others. By knowing the quality, processors can avoid purchasing grain that does not meet their needs. There are a lot of methods used to determine the technological quality of kernels. A number of these are time consuming and expensive (farinograph, alveograph), and hence are often impractical to use as the way to pay producers premiums based on kernel quality expectations. Finding measures of wheat which can be conducted quickly and less expensively gives the opportunity to develop new approaches to predict kernel or dough behavior. Between them, the research on mechanical properties of kernels continues to expand.Mechanical properties of wheat kernels are naturally associated with the conditions of mechanical separation of the endosperm and the outer bran layer, the breaking resistance of the bran or the breaking susceptibility of the endosperm itself, or starch and proteins. Khazaei and Mann [1] stated that the relaxation data could be useful in estimating the susceptibility of materials to damage. Ponce-García et al. [2] successfully applied rheological measurements to distinguish among wheat classes, varieties, and different moisture contents. The test on intact kernels was used by Figueroa et al. [3,4] to establish relationships among protein composition, viscoelasticity of dough, and baking outcomes. However, there are many different conclusions and o...

Examination of the Peleg and Normand equation during relaxation of wheat: The effect of holding time

“…Thus, the study is a continuation of previously published works on the impact of the initial load level on model coefficients (Al Aridhee et al, 2019; Łysiak, Kulig, & Wójcik, 2019). Herein, we analyzed the variability of the coefficients of the Peleg and Normand model and its accuracy for the relaxation experiments differed in holding time duration.…”

“…Practically, a viscoelastic solid deformed at slow strain rate relax during the deformation stage. In previous studies, no clear influence of the deformation level on the parameters of the Peleg and Normand model was observed (Al Aridhee et al, 2019). With regard to the deformation rate, it can be assumed that this effect may be particularly noticeable for kernels with higher moisture.…”

“…With regard to the deformation rate, it can be assumed that this effect may be particularly noticeable for kernels with higher moisture. Their relaxation profiles are more liquid like, for which both higher relaxation during the first phase of the test and higher decay are observed (Al Aridhee et al, 2019; Łysiak, 2007). Hence, it may be stated that due to the strain rate effect an additional correction of the parameters may be necessary.…”

“…The measurements were made for intact wheat kernels with seven levels of moisture content with the procedures similar to those applied in (Al Aridhee et al, 2019). Prior to the loading mass and basic dimensions (thickness, width and length) of each single kernels were determined with a caliper.…”

“…Out of these models those of Maxwell, Maxwell‐Wiechert, standard linear solid (SLS), Burgers or Kelvin‐Voigt in the case of creep, or the equation of Peleg and Normand are most frequently used. Brief summary of research in this area has been included in the previous authors' work of Al Aridhee, Łysiak, Kulig, Wójcik, and Panasiewicz (2019), in which the effect of initial load on the Peleg and Normand model was verified. Therefore, we present here briefly the studies of the Peleg and Normand equation and of the impact of the duration of the relaxation experiments on some relaxation results.…”