Water sorption characteristics of six row barley malt ( Hordeum vulgare)

Abstract

The water sorption isotherms of six-row Belgian barley malt (Plaisant) were determined for a temperature range between 15°C and 35°C. The results obtained showed that for water activity ( a w) values below 0.5 the effect of temperature on the sorption isotherms was negligible. For a w values above 0.5, an increase of the equilibrium moisture content with temperature at a given a w was observed, as reported by other authors in products rich in sugars. Due to the malting process, barley malt presents a higher simple sugar content than nonmalted barley. The experimental data was fit to various sorption models. The constants obtained for each equation and the correlation coefficients were presented. From these, it was found that the Brunauer–Emmett–Teller (BET) and Kuhn models showed the highest correlation coefficients for a w below 0.50. For a w values above 0.50, the best fitting was obtained for the models of Harkins–Jura, Smith and Henderson, although other models such as Freundlich, Chung–Pfost and Guggenheim–Anderson–De Boer (GAB) also showed good fitting. Due to the fact that the practical storage moisture content of barley malt is below 60 g/kg, the BET model (suitable for a w<0.50) would represent the best model to apply for this product. The monolayer water content calculated from the BET and GAB equations ranged between 42.5 and 43.9 g/kg (dry basis), and 46.0 and 51.0 g/kg (d.b.), respectively, for the range of temperature considered in this work (15–35°C). These values corresponded to a w values ranging from 0.16 to 0.19, according to the BET equation and from 0.19 to 0.21 using the GAB equation. The average sorption enthalpy ( Q s) and the total heat requirement (Δ H T) of this process (15–35°C) showed values of 7.787±0.262 and 51.834±0.275 kJ/gmol, respectively.