Moisture sorption isotherms of sorghum malt at 40 and 50°C (original) (raw)
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Moisture sorption isotherms of sorghum malt at 40 and 50º C
The desorption and adsorption equilibrium moisture isotherms of sorghum malt at the temperatures of 40 and 50 1C, over the water activity range of 0.1–0.9, were determined using the static gravimetric method. A non-linear regression programme was used to fit five moisture sorption isotherm models [Modified Henderson, Modified Chung-Pfost, Modified Guggenheim–Anderson–de Boer (GAB), Modified Halsey and Modified Oswin] to the experimental data. The models were compared using the standard error of estimate, mean relative percentage deviation, fraction explained variation and residual plots. The Modified Chung-Pfost model was found to be the best for predicting the desorption equilibrium moisture content, while the adsorption equilibrium moisture content was best predicted by the Modified Oswin model. The desorption and adsorption water activities were found to be best fitted by the Modified Oswin model. The moisture sorption isotherms were sigmoidal in shape and showed a marked effect of temperature. The span of the moisture sorption hysteresis loop formed, decreased with increase in temperature, while the size increased with increase in temperature. r 2005 Elsevier Ltd. All rights reserved.
Mathematical Models for Moisture Sorption Isotherms of Barley and Wheat
Moisture sorption isotherms play an essential role in preservation and storage of dehydrated foods. To study the behavior of different cereals (wheat, barley), in a certain equilibrium static environment, gravimetric methods were applied for temperatures ranging between 16 and 25°C and water activities from 0.533 to 0.909. The moisture isotherms were sigmoid shaped and showed a clear temperature dependence of water activity (aw). GAB and a second order polynomial equation were used to model the experimental data.
Brazilian Journal of Food Technology
The saturated salt slurry method has been a standard method for many years, but there are several drawbacks, including long equilibration times, extensive labour and mould growth at high water activity (aw) values. The validity of the dynamic method (automated sorption instrument) was investigated by comparing it with the equilibrium isotherms obtained using the saturated salt slurry method for two food materials (whole sorghum raw flour and whole grain sorghum extrudates), as well as their diffusion coefficients. The sorption isotherms ranged between 11.3% and 84.3%. The equilibration time for the highest water activity (0.843) was about 30 days using the saturated salts method, considerably longer than using the dynamic method (300 min). For raw sorghum flour, the dynamic method values were consistent with the data obtained using the traditional method, which can be confirmed by the similar curves and monolayer values obtained (0.038 and 0.040 g water / g solids for the salt slurr...