Análise e modelagem do processo de criocongelamento e crioconservação de sementes de amendoin, cunha e sorgo.

Abstract

The germplasm of plant species represents an important natural resource of high priority for the world, as it derives solutions for hunger, for the development of new drugs, in addition to feeding biotechnology and genetic engineering. Cryopreservation allows the conservation of biological materials for long periods of time, with a minimum of genetic erosion and becomes the basis for the development of new cultivars, allowing greater productivity in the agricultural and agro-industrial sectors. In this context, the objective of this research was to determine the freezing kinetics of peanut (Arachis hypogaea L.), sorghum (Sorghum bicolor L.) and cunhã (Clitoria ternatea L.) seeds at temperatures of -20oC, -50oC, - 100oC and - 150oC, as well as its cryopreservation at these same temperatures for a period of time (12 months), determining its physiological quality. To determine the freezing kinetics of seeds, a data acquisition system was developed, using microthermopares whose measurable temperature range was -170 to 180oC, with an accuracy of ± 0.5oC. The analysis of the experimental data was performed in the Matlab 7 software, using the Gauss-Newton nonlinear regression method, in mathematical models based on the Fourier heat transfer equation. From the kinetic behavior of the frozen seeds, it was possible to determine physical phenomena and thermodynamic parameters, such as effective thermal diffusivity, activation energy, entropy, enthalpy and Gibbs free energy. According to the results obtained, it appears that the Model II of Cavalcanti-Mata & Duarte is the one that best represents the kinetic behavior of the freezing of the seeds, in order to have the lowest relative average error P (%) for all temperatures, as well as the highest R2 determination coefficient. With the Fourier Model, using the first term of the series, and Cavalcanti Mata & Duarte's Model I, it was possible to determine the effective thermal diffusivity for peanut, wedge and sorghum seeds, and this diffusivity increases with decreasing temperatures studied. The activation energy was 1.04 kJmol-1 and 2.21 kJmol-1 for peanut seeds, respectively for the Fourier model and the Cavalcanti-Mata & Duarte model I; 6,353 kJ mol-1 and 2,789 kJmol-1, respectively, for the cunhã seed; and 6,671 kJmol-1 and 3,927 kJmol-1 respectively for sorghum seeds. Enthalpy and entropy increased with decreasing temperature and Gibbs free energy decreased with decreasing temperature, for all seeds under study. Regarding the physiological quality of the seeds, it was found that the germination and vigor of the seeds were not altered when stored at -150oC for a period of 12 months for the seeds of wedges and sorghum and 3 months for the peanut seeds, indicating that these seeds can be cryopreserved for an indefinite period of time.