CHANGE OF STRESS CRACK IN CORN KERNEL DURING ITS PREPARATION FOR PROCESSING
Authors: Rybchynskyi R. 
Published: July 2020

The article presents the results of the study of the influence of stress crack in corn kernel on the change of its mechanical properties, namely, on the strength of kernel and its ability to grind during the technological process of preparation for processing. The research was conducted at the Dnipro Food Concentrates Plant. It is established that percentage of damage, i.e. grain impurities and foreign material (impurities), when receiving grain at the production elevator is within the norms of State standards of Ukraine (DSTU 4525:2006) – up to 7 % and not more than 1.0 %, respectively. But in the process of grain transportation this index is increasing. The maximum level of grain impurities (9.1 %) in corn grain can be observed before its preliminary cleaning on the separator BSH-100, then this indicator decreases significantly to 1.8 % in the cleaned grain, but then increases again in the technological process. Moreover, before sending grain into the degerminator the level totals 4.8 % - almost as much as when receiving grain from vehicles. One can say the same regarding the level of foreign material. Its minimum amount in the grain after pre-cleaning (0.5 %), and the maximum – at the end of the cleaning stage (7.4 %), which is much more than when receiving grain. The increase in the amount of broken grain (including that relating to impurities) in the technological process is accompanied by higher number of stress cracks in the corn kernel. During receiving, the studied grain has already had a high stress crack – 68 %. At the same time, there was more corn kernel with one crack (41 %). After transportation by a belt conveyor and the main high-performance bucket elevator, although the total stress crack increased not significantly – up to 75 %, but there were changes in the number of cracks: the number of kernels with one crack decreased to 22 %, but the number of kernels with many (three or more) cracks increased from 8 to 33 %, respectively. During further transportation and processing of corn kernel, the stress crack increased to a maximum value of 78 % (before separation on SAD-10-01), and then decreased to 72 % in the grain entering the degerminator. It is established that the decrease in corn kernel strength is influenced by both the total stress crack and its nature, i.e. the number of stress cracks in each kernel. The maximum required force for the corn kernel damage was observed exactly for grain entering the intake pit – 3.6 kg / 50 kernels. Here you can find more corn kernels stressed by only one crack (single) – 41 % or without cracks – 32 %. And the minimum effort – 3,0 kg / 50 kernels - for cleaned grain after conveyor and elevator No. 1, where the share of kernels with multiple stress crack (3 or more cracks) totaled 43 % (only 22 % of kernels were without cracks). A high inverse correlation of -0.84 was established between the number of stressed kernels with three or more cracks and the effort to break corn kernel. Based on research, it is recommended to use the index of stress crack in corn kernel to assess its quality when accepted for further processing, as this indicator is directly related to the yield of finished products. Key