Abstract
ABSTRACT Knowledge of the water sorption phenomenon in Brazil nut seeds will allow proper handling of this product, especially with regard to adequate conditions for safe storage. Thus, the present study aimed to determine the sorption isotherms (desorption and adsorption) of Brazil nuts, fitting different mathematical models to the experimental data, as well as to examine the hysteresis effect. To obtain the sorption isotherms, the static method was employed at temperatures of 25, 35, 45 and 55 °C and air relative humidities varying from 10 to 80%. The psychrometric conditions of the air were acquired with the aid of acid solutions and specific saturated saline left inside desiccators with the samples. It was verified that for a given isotherm, the equilibrium moisture content of Brazil nuts increases with water activity increment. In addition, at a constant water activity, equilibrium moisture content decreases with temperature increase. The Copace, Henderson and Oswin are the models that best describe the hygroscopicity of the Brazil nut seed for both the adsorption and desorption processes. Hysteresis was more pronounced at lower temperatures and higher values of water activity. The moisture content value for storage at temperatures less than 55 °C, without the risk of fungal development, must be lower than 8.2% (d.b.).
Highlights
The Brazil nut tree (Bertholletia excelsa) is a species that occurs in highlands across the Amazon Basin
Some of the Brazil nut seeds with the initial moisture content were used for the desorption process, and the remaining seeds were dried at 60 °C and 8% air relative humidity to a moisture content of 2.0% (d.b.) for the adsorption process
While the mean relative error indicates the percentage of the average error present in the model, the standard error (SE) indicates the average error of the model at the same physical units of the variable used in the study; in this case, moisture content
Summary
The Brazil nut tree (Bertholletia excelsa) is a species that occurs in highlands across the Amazon Basin. Bolivia is the leading exporter of Brazil nuts, which are the dehulled product with the highest market value, corresponding to approximately 60.4% of the world market share, while Brazil is responsible for 4.5% (FAO, 2017). In 2009, Brazil was responsible for 64.1% of worldwide exportation of Brazil nuts in their integral form (with the hull), while Bolivia was the main buyer. This difference in products exported with and without the hull is due to the low technology involved in the production chain in Brazil and lack of information regarding post-harvest procedures for this product, including conservation. Variables that assure the correct conservation of a grain or seed (moisture content, for instance) are determined using knowledge of the relationship between the product, the temperature, and the water activity of the product or the relative humidity of the air at equilibrium (Corrêa et al, 2014, 2015)
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