Avaliação da preservação da atividade antioxidante de sementes de milho submetidas à secagem contínua e intermitente

Abstract

Brazil has high production in grains, with corn being the third most cultivated cereal in the country. Seed is harvested with a moisture percentage of 25¬28% on dry basis (d.b.) and must be at levels of 12.5¬14% (b.s.) to be stored, requiring the drying process. In this sense, the objective of this work was to study the intermittent and continuous drying in kiln, in order to preserve of antioxidant compounds. The influence of the solvent and extraction time on the antioxidant activity of the seeds was studied. Seeds in natura were extracted with the solvents methanol/water 70/30 (v/v), methanol/water 95/5 (v/v), ethanol/ water 70/30 (v/v) and ethanol/water 95/5 (v/v), during the times of 1, 4 and 24 hours, and evaluated for antioxidant activity by DPPH and ABTS radicals scavenging and Fe(II) chelation ability. Best results were obtained with extracts MeOH:H2O 70/30 prepared in 4 hours by DPPH and ABTS methods, and EtOH:H2O 70/30 prepared in 4 hours for the chelation ability method. Seeds were dried in continuous and intermittent drying at temperatures of 40°C, 55°C and 70°C and tempering times of 5 and 10 minutes. MeOH:H2O 70/30 4h extracts were prepared with the dehydrated samples and their antioxidant potential was evaluated by the DPPH and ABTS methods. EtOH:H2O 70/30 4 h extracts were evaluated for their chelation ability. A decrease in the antioxidant potential was observed in all extracts obtained after drying, with the lowest losses for the three tests for extracts obtained from intermittent drying of 5 and 10 minutes at a temperature of 40°C. In all studies, the high temperature of drying had a negative influence on the antioxidant activity of the seeds, which may be related to the decomposition of the bioactive compounds of corn, demonstrating that the employability of intermittent drying at low temperatures is an effective alternative in maintaining the compounds antioxidants in corn. Then, the DPPH and ABTS reaction kinetic models were adjusted, obtaining correlation coefficients of 0.993 and 0.977, respectively. Reaction orders were 4 and 5, respectively, with activation energy varying between 14.4 – 93.4 kJ mol-1 . In addition, global coefficients of heat and mass transfer by convection and energy consumption were determined, both for conventional and intermittent drying. Adequate adjustments were observed for the average heat transfer coefficient with na overall deviation of around 5.0% and the value of 13.696 W m¬2 °C¬1 , and for the global mass transfer coefficient, the linear type equation was better suited to the values obtained for intermitente drying of corn seeds with an overall deviation of 10.0%. In relation to energy consumption, with the employability of intermitente drying at a temperature of 40 C and tempering time of 10 minutes, the lowest energy expenditure was obtained, being the most economically viable condition.