Efeito do tratamento térmico nas propriedades físico-químicas, reológicas e térmicas no processamento de milho

Abstract

Zea mays is produced in every continent of the world and used in food production in various forms for direct consumption by humans and indirectly by ingestion of animal products where it is used as one of the feed ingredients. The physical characteristics of the corn kernels may vary within the lot, genotype and culture site. The grains also vary its characteristics due to infestation by insects, fungi proliferation, physical integrity, storage and processing conditions. The thermal treatment temperature can increase the percentage of broken grains, weight loss and susceptibility to defects, resulting in a reduction in the values of metabolizable energy and changes in thermal properties and processed corn paste. The objective of this study was to study the effect of heat treatment, performed at different temperatures, on the physical, chemical, rheological and thermal properties of degerminated maize grains. The work was carried out using two cultivars of maize, harvested 2017, harvested with high moisture content and submitted to the thermal treatment at temperatures of 45 ºC, 90 ºC and 180 ºC until storage humidity. There were performed in the maize samples, chemical characterization, germination, milling and laboratory analysis. The results were submitted to analysis of variance (ANOVA) at the 5% level of significance and, in the significant models, the means were compared by the Tukey test at 95% confidence interval. The results showed that the controlled application of heat and humidity modifies the physical, chemical, rheological and thermal properties of maize, promoting changes in the gelatinization temperatures of the starch, gel hardness, swelling power and solubility. The heat treatment temperatures altered the corn starch morphology, observed by scanning electron microscopy, showing differences in dispersion and size of granules. In grain pathology, the effects of temperature were favorable, reducing fungi in grains submitted to higher temperatures. In the analysis of thermal properties of the product was verified adverse effects on the texture profile due to the conditions of temperarature of heat treatment. The heat treatment temperature that best preserved the technological characteristics of the corn was 45 ° C, evaluated through the analysis of physical-chemical properties and processed corn paste. With the elevation of the heat treatment temperature, losses of technological quality were observed, which are irreversible and require care and controls in the conditions used to reduce the moisture content in corn grains.