Cinética de secagem, propriedades físicas e higroscópicas dos frutos e caracterização do processo de torrefação dos grãos de Coffea canephora

• Ano de defesa: 2012
• Autor(a) principal: Botelho, Fernando Mendes
• Orientador(a): Correa, Paulo César
• Banca de defesa: Resende, Osvaldo , Donzeles, Sergio Mauricio Lopes , Lacerda Filho, Adílio Flauzino de
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de Viçosa
• Programa de Pós-Graduação: Doutorado em Engenharia Agrícola
• Departamento: Construções rurais e ambiência; Energia na agricultura; Mecanização agrícola; Processamento de produ
• País: BR
• Palavras-chave em Português: Processamento; Beneficiamento; Pós-colheita; Torrefação, Coffea Canephora
• Palavras-chave em Inglês: Processing; Coffea canephora; Post-harvest procedures; Roasting
• Área do conhecimento CNPq: CNPQ::CIENCIAS AGRARIAS::ENGENHARIA AGRICOLA
• Link de acesso: http://locus.ufv.br/handle/123456789/736

Traditionally, coffee is one of the most explored cultures in Brazil and the country owns the productive and processing technologies of this product. However, the producer s interest, the search of quality improvements and research support were historically on a secondary basis for Coffea canephora in comparison with Coffea arabica. This trend resulted in lack of information, mostly, of the post-harvest procedures of this specie. Thus, the objective of this work was to study the drying kinetics, the physical and hygroscopical properties of Coffea canephora fruits, and also to characterize the roasting procedure of the processed product. C. canephora fruits manually harvested at a commercial plantation at the Nova Santa Helena city (MT, Brazil) were used, while the processed product was acquired at Cooperativa dos Cafeicultores da Região de Lajinha (Cocafé), Lajinha (MG, Brazil). Hygroscopic and thermodynamic properties were obtained during water desorption and adsorption on coffee fruits in different psychometric air conditions. Kinetics and thermodynamic properties of the drying process at different air temperatures were acquired. Also, the main physical properties of fruits throughout the drying process (repose angle, bulk and real density, porosity, one thousand mass, sphericity, circularity, volume, area, equivalent diameter, characteristic dimensions, surface-volume relationship, real and bulk volumetric shrinkage) were attained. It was also evaluated, for the roasting process, which relationship among time and roasting temperature that resulted a better cup quality, in addition with the analysis of some physical characteristics of the grain (bulk volumetric expansion index, bulk density, moisture content and color) during roasting. The results allowed the following conclusions: a) as most of hygroscopic products, equilibrium moisture content of C. canephora fruits was directly proportional to the relative humidity and decreases with temperature increase at a constant value of relative humidity, being that the Sigma-Copace model the one that best fitted the experimental data. A reduction of moisture content lead to an increase of energy (isosteric heat of desorption) required to remove water from the product and increased the amount of energy release (isosteric heat of adsorption) by water adsorption of the product. Furthermore, to a constant value of moisture content, integral isosteric heat of desorption were higher than the values of adsorption. This trend is similar to the behavior presented by differential entropy; b) Physical properties studied were influenced by moisture content, being that, with the exception of surface-volume relationship, entire properties reduced their values throughout drying. A three degree polynomial equation was the one that best described bulk and real volumetric shrinkage of C. canephora fruits. c) Page and Midilli models best represented drying curves of C. canephora fruits. Effective diffusion coefficient increased with increment of drying air temperature, presenting values between 2.282 × 10-11 and 4.316 × 10-11 m2 s-1, to the temperature range of 40 to 60 ºC. Activation energy for diffusion process was 38.016 kJ mol-1 and thermodynamic properties (enthalpy, entropy and Gibbs free energy of activation) increased with drying air temperature increment. d) Grain mass temperature, roasting temperature, grain weight loss and time presented a linear dependence among each other and with roasting degree. C. canephora grain received higher points by cup test when they were roasted on the temperatures of 247, 274 and 296 ºC until average light roast degree and for average roast degree this trend occurred at the temperature of 247 ºC. Generally, coffee lost quality when it was roasted at higher temperature value (308 ºC) and with the increment of roast degree. Moisture content reduced continuously until average light roast degree, and, in general, there was a bulk density and color coordinates (L*, a* and b*) reduction, in addition with increase of grain volume, mostly at the end of roasting procedure at all roast temperatures analyzed. With the exception of bulk density, there was no correspondence between remaining physical properties and cup test evaluation.