Absorção de água por grãos de milho com diferentes níveis de danificação mecânica

• Autor(a) principal: Botelho, Fernando Mendes
• Data de Publicação: 2009
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/3536
• topic: Maceração; Propriedades físicas; Propriedades mecânicas; Maceration; Physical properties; Mechanical properties; CNPQ::CIENCIAS AGRARIAS::ENGENHARIA AGRICOLA

The aim of this work was to evaluate and model the water absorption process of corn grain submitted to soaking process at different levels of mechanical damage at different temperatures, as well to determinate and model its mechanical behavior during the process. Behavior of some physical properties was investigated in function of moisture content. Corn grain of AG 1510 variety were utilized, with initial moisture content of 0.142 (decimal d.b.) obtained at a small producer from Viçosa (MG) city area. Different mechanical damage levels were induced at grains, correlating with electrical conductivity. At soaking process, solution of 0.2 % of sulfur dioxide (SO2 ) and 0.55 % of lactic acid (C3H6O3) in distilled water were used, referring to wet milling conventional process of corn grain, at temperatures of (40, 50, 60 and 70) ºC and mechanical damage levels analyzed indirectly through electrical conductivity of (2.847, 14.077, 22.261, 29.194 and 32.971) μS cm-1 g-1. Soaking process modeling was performed by Peleg s model. Effective diffusivity coefficient to hydration process of corn grain was obtained through observed data adjustment of liquid diffusivity model based on Fick s second law, and its relationship with temperature was described by Arrhenius equation. Bulk and real densities, porosity, circularity, sphericity and volumetric expansion were evaluated to corn grain without induced mechanical damage (witness) in function of moisture content. Mechanical properties were also determined: force to a specific deformation of 0.001 m, proportional deformity modulus, deformation energy and resilient modulus, evaluating the force-deformation curve, to different moisture content and physical damage levels. Was concluded, according to obtained results: (a) structural alterations caused by induced mechanical damage at corn grain altered product water absorption rates; (b) Peleg s model adequately adjusted to observed data to entire conditions utilized; (c) effective diffusivity coefficients values increased with temperature and damage level increase, presenting magnitudes between (2.403 × 10-10 and 19.220 × 10-10) m2 s-1; (d) activation energy referred to water diffusivity of corn grain varied from (14.533 to 28.366) kJ mol-1, being that higher values is correlated to higher product physical integrity; (e) porosity increased linearly until achieve a certain level, and its behavior was described by a bi-segmented model. Bulk and real densities varied by a quadratic relation, where by values decreased until attain a minimal value, increasing afterwards. Circularity and sphericity of corn grain didn t varied with moisture content; (f) Unit volumetric expansion was best represented by Rahman s model. None of the conventional models used to predict volumetric variation of agricultural products adjusted satisfactorily to apparent volumetric expansion observed data of corn grain, therefore a new model was proposed; (g) The mechanical properties evaluated decreased significantly only with regard to moisture content variation. Force, proportional deformity modulus, energy and resilient modulus values acquired varied respectively between (446.1 and 144.60) N; (532.76 and 165.9) MPa; (279.32 and 36,24) mJ, and (1.4687 and 0.1923) mJ mm-3, with the moisture content ranging from (0.2585 to 0.5878) (decimal d.b.) and mechanical damage level obtained indirectly through electrical conductivity between (2.8466 and 32.971) μS cm-1 g-1; (h) sigmoid model, expressed by Taylor series, satisfactorily described the force-deformation relationship data displayed by corn grain with a moisture content below 0.57 (decimal d.b.).