202 Acta Technologica Agriculturae 4/2021 Ľubomír Kubík, Monika Božiková, Viera Kažimírová Wheat is exploited mainly for mill-bakery processes. The endosperm of wheat grain comprises approx. 83% of the kernel weight and is a source of white four. The endosperm contains the greatest share of protein, carbohydrates, iron and major B vitamins, such as ribofavin, niacin and thiamine. The endosperm is also a source of soluble fbre. Bran makes up approx. 14.5% of the kernel weight. It contains a small amount of protein, large quantities of the three major B vitamins, trace minerals and dietary fbre – primarily insoluble (Flour.com, 2020). Thermophysical parameters are signifcant characteristics that can be used for improvement of technological processes. If the basic thermal parameters are known, it is possible to determine optimal storage conditions (Božiková et al., 2015). Raw wheat is irreplaceable in production of raised bakery products. Furthermore, it is also used to produce diferent sorts of bakery products, breakfast cereals, pastries, etc. Wheat utilization is also increased due to food purposes. Wheat grain becomes inseparable component of the feedstufs; it is used for production of the starch and ethanol (Kulp and Ponte, 2000). Triticum aestivum L. is the most important bread plant. Physical and mechanical properties of grains are necessary for designing the facility of storage, handling and processing of agricultural products (Seif and Alimardani, 2010). Knowledge of apparent elastic properties such as Poisson’s ratio and elastic modulus of agricultural seeds is important for the prediction of their load-deformation behaviour and design of their processing machines. The risk of damaging and cracking the seeds during harvesting, conveying and processing is high. Therefore, to analyse the efect of cracking on deterioration of seed resistance to fracture, it is necessary to determine the fracture characteristics. There is a simple relationship between fracture characteristics and modulus of elasticity. The modulus of elasticity can be determined using diferent techniques, determination of fracture characteristics is the main beneft of applying fracture method (Khodabakhshian and Emadi, 2011). The mechanical properties of wheat grains have been considered both as single grains, with multiple grains together, and as individual bran layers through multiple approaches. Turnbull and Rahman (2002) studied the complex properties of the wheat texture of endosperm. Compression of the wheat endosperm was studied by Budny et al. (2016) and Dobraszczyk et al. (2002). Tensile loading was applied to whole grains or bran layers (Antoine et al., 2003). Hemery et al. (2010) investigated the fracture mechanics of grains. The aim of paper was to determine the mechanical properties of winter wheat grains Triticum aestivum L. The properties are relevant in terms of mechanical condition evaluation of grains. The grains were submitted the compression between two parallel steel plates. The stress- strain loading curves were plotted and the failure strengths of grain bran and of whole grain were determined. Moduli of elasticity of grains and the apparent energy densities at failure strength of bran and on the level of grain failure strength were determined. The bran border structure of central inner part of grains was studied on microscope sections of the longitudinal cuts of the grains using image computer processing. The presence area of starch in bran border of the grain central section was selected by the computer image processing. The area proportion of the Acta Technologica Agriculturae 4 Nitra, Slovaca Universitas Agriculturae Nitriae, 2021, pp. 202–208 MECHANICAL PROPERTIES OF WHEAT GRAINS AT COMPRESSION Ľubomír KUBÍK, Monika BOŽIKOVÁ*, Viera KAŽIMÍROVÁ Slovak University of Agriculture in Nitra, Slovak Republic Hook’s law for evaluation of the modulus of elasticity of wheat grains and its general behaviour under compressive loads were studied. Whole specimens were subjected to compressive loading between metal parallel plates. The mechanical properties of grains were determined in terms of average failure strengths of grain bran and whole grain; deformation; and modulus of elasticity. The mechanical properties of very dry grains of the winter wheat Triticum aestivum L. with the moisture content of 10.3% were studied. The failure strength of grain bran was 4.43 MPa at the deformation of 10.7%, and the failure strength of whole grains was 4.88 MPa at the deformation of 13.5%. The modulus of elasticity of grains was 43.67 MPa. The apparent energy density at bran failure strength was 0.261 MJ·m -3 , and 0.470 MJ·m -3 on the level of grain failure strength of the whole grain. The bran border structure of central inner part of grains was studied using microscope digital sections of longitudinal cuts of the grains using the image computer processing method. The area proportion of starch and pericarp of the border parts of grains was studied to describe the border texture of central sections of grains. Keywords: wheat; modulus of elasticity; failure strength; apparent energy density; structure DOI: 10.2478/ata-2021-0033 Contact address: Monika Božiková, Slovak University of Agriculture in Nitra, Faculty of Engineering, Institute of Electrical Engineering, Automation, Informatics and Physics, Tr. Andreja Hlinku 2, 949 76 Nitra, Slovak Republic; e-mail: monika.božikova@uniag.sk