Sorption isotherms of Brazil nuts

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.).

Comparison between desorption isotherm curves of ryegrass (Lolium multiflorum L.) and flax (Linum usitatissimum L.) seeds

“…Figure 4 confirms the temperature influence over the desorption isotherms of ryegrass and flax seeds. At a constant water activity, the equilibrium moisture content diminishes with increasing temperatures, a trend that is reported for most agricultural products (Goneli et al, 2010;Corrêa et al, 2016;Goneli et al, 2018;Botelho et al, 2019;Zeymer et al, 2019). According to McLaughlin and Magee (1998), this trend is explained by the molecules' excitation state.…”

“…According to Sheskin (2004), R 2 defines the model success, as it evaluates the experimental data variation. However, this statistical parameter is not a reliable decision-making tool for nonlinear models, being an indicative index of the best model (Botelho et al, 2019). A model adequately represents experimental data when the MRE is less than 10% (Costa et al, 2015) and when SEE values are lower (Draper;Smith, 1998).…”

Drying in Brazil Nut Processing as Tool for Prevention of Contamination by Aflatoxins

“…Costa et al (2017) found that this system reduced the moisture content of the nuts by 78.2% after 150 days, however this reduction was not fast enough to avoid contamination completely, and potentially produced filamentous AFL fungi .The Aw of nuts ranged from 0.99-0.52, showing a trend of reduction over storage time. According to Botelho et al (2019), to reduce the risk of fungal development, the Brazil nut must be stored at temperatures <55 °C and the mc content must be <8.2%. In our study, at the plant where the dried samples were collected, the average drying temperature in the oven at the end of the process is 70 º C, but the storage of the finished product is between 25-30 º C. Therefore, it is essential that the study uses the study of Brazil nut sorption isotherms as tested by Chisté et al (2007), in which it was observed that to ensure microbiological stability (Aw <0.6), the nut moisture content should not be greater than 1.62 g%.…”

USE OF AIC AND BIC IN DESORPTION ISOTHERMS OF TAMARIND SEEDS (Tamarindus indica L.)

“…The desorption isotherm curves estimated by the model (Figure 1) showed that, for the same range of moisture content, water activity values increase as the temperature increases. It is a response found in the isotherms of various plant products in the literature, such as yellow mombin (Spondias mombin L.) pulp in foam (Cavalcante et al, 2018), sunflower seeds (Helianthus annuus L.) (Campos et al, 2019), and brazilnuts (Bertholletia excelsa H. B. K.) (Botelho et al, 2019).…”