Abstract
The effects of drying conditions on the shrinkage of Coffea Arabica L., cultivar Catuaí Vermelho, were studied. An exponential model derived from the kinetic model was used to describe the shrinkage kinetics. In addition, an equation was proposed to describe the relationship between the superficial areas and weights of the coffee berries. Coffee berries were dried at temperatures (T) of 35, 45, 55 and 65ºC and at relative humidities (φ) of 25, 35, 45 and 55%, forming 16 different sets of conditions, with an initial moisture content for all conditions of 2.27 dry basis (d.b.), dried until 0.11 d.b. Changes in the product dimensions were measured continuously during drying. Surface area-to-volume ratio values increased with moisture content decrease. The model was suitable for representing the shrinkage kinetics, as well the empirical equation for predicting surface area. Temperature had a greater influence over the constant rate of change of the characteristic dimension (k values) than φ. Activation energies were also determined to have magnitudes of 39.31, 37.32, 36.28 and 36.22 kJ mol-1 for relative humidities of 25, 35, 45 and 55%, respectively.
Highlights
The drying or dehydration of foods is one of the most common methods for assuring the quality and stability of agricultural products, decreasing the water activity of the material, reducing the biological activity, and reducing the chemical and physical changes of the material during storage
The constant rate values (k) for Catuaí Vermelho cultivar in each T and φ combination are shown in Table 1, in which k values were analyzed varying along with T and φ (Figure 2) in order to assess which factor had the highest influence over k
Krokida et al (2000) considered that the temperature is the parameter with the most influence over food drying kinetics, and Afonso Júnior et al (2004) observed this trend for coffee berries
Summary
The drying or dehydration of foods is one of the most common methods for assuring the quality and stability of agricultural products, decreasing the water activity of the material, reducing the biological activity, and reducing the chemical and physical changes of the material during storage. The volumetric behavior of a grain or fruit, during the drying process, is important to estimate tension levels that the product is submitted, as well when developing equipment, processes and simulation models. This behavior is dependent of temperature and humidity gradients. 423-428, 2011 the superficial area, shape and dimensions of an agricultural product are crucial data for mass and heat transfer studies as well as for airflow within a granular mass of the product These parameters and additional information, such as moisture content, are used for predicting storage and drying conditions of grain and cereals and quality losses during the post-harvest period
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