Secagem e armazenamento de grãos de milho do centro e das extremidades da espiga: efeitos sobre as propriedades físico-químicas dos grãos e do amido isolado

Abstract

Most corn cultivars have an insertion of grains with different dimensions along a corncob, with the grains from the extremities with a spherical shape and the grains from the center with higher length and lower thickness. These differences in grain dimensions can affect corn properties, as drying kinetics may be different between grains from the center and extremities. In addition, the consistency of the corn endosperm may be different, where the corn from the extremities has a higher presence of vitreous endosperm, which can modify the drying parameters and the effects of the operation on the quality of the grains. These differences can affect drying conditions, which can lead to latent effects of this operation during corn storage. Thus, the objective was to evaluate the effects of drying and storage conditions of corn from the center and extremities of the corncob on the physicochemical and technological properties of the grains and isolated starch. The effects of drying temperature (60, 80, and 100 ºC) on the quality of corn grains and isolated starch, and the effects of storage temperature (15 and 25 ºC) and storage time (0, 3, and 6 months) on the quality of corn from the center and extremities, separated before and after the post-harvest stages were evaluated. Drying kinetics were quantified by drying time, drying rate, and effective moisture diffusivity. Grain quality was measured by grain classification and evaluation of corn starch, protein, and lipid properties. At higher drying temperatures (80 and 100 ºC), the drying rate and the effective moisture diffusivity of the grains from the center were higher concerning the grains from the extremities. Significant changes were observed in the protein properties of the grains, mainly the reduction of the solubility and inactivation of the lipase enzyme, and the reduction of the lutein and β-carotene contents in the grains from the center, separated after drying. The increase in drying temperature resulted in a reduction in the yield and purity of the extraction and increased the thermal resistance of the starch. The results showed that industrial separation of grains with different dimensions can increase the starch extraction yield by 35 – 40%. The separation of grains from the center and extremities of the corncob during the post-harvest phases can increase the amount of not defective grains by more than 2% after 6 months of storage at 25 °C. After this study, some research gaps were found: a) breeding studies to search for new genotypes with higher uniformity of grains along the corncob, and b) addition of a stage of separation of corn grains with different dimensions before drying/storage.