Impact of Moisture Content and Loading Rate on Kernel Damage and Mechanical Properties of Bread and Feed Wheat Kernels

Compression tests are widely used to characterize cereal kernels, yet the loading rate is often treated as a secondary methodological factor, despite the fact that the ASAE S368.4 procedure recommends a low crosshead speed, whereas industrial size-reduction operations involve much faster and more complex loading conditions. This mismatch limits the direct transfer of laboratory data to milling practice and makes it difficult to compare results obtained under different test settings. The aim of this study was therefore to determine how grain moisture content and loading rate (crosshead speed) affect kernel damage and selected mechanical properties of bread wheat cultivars (Bataja and Tytanika) and feed wheat cultivars classified in the Polish C quality group (Lawina and Sikorka). Before the analyses, kernels were adjusted to five moisture levels: 10%, 12%, 14%, 16%, and 18% on a wet basis (w.b.). Compression tests were conducted at six crosshead speeds: 1, 3, 5, 10, 30, and 50 mm min−1. The conversion ratio of mechanical properties determined relative to 1 mm min−1 and 10% moisture content ranged from 0.46 to 2.59, confirming that both factors markedly changed kernel response. Rupture force generally decreased with increasing moisture content, whereas longitudinal strain, relative strain and rupture energy increased. A distinct decrease in all mechanical parameters was observed at 10 mm min−1, and this effect became more pronounced at higher moisture contents. The results indicate that the loading rate should be reported and controlled in wheat kernel compression tests and should be considered when laboratory measurements are used to support milling optimization. However, the proposed value of 10 mm min−1 should be interpreted as a promising laboratory reference point rather than as a direct industrial operating standard.