Sorption isotherms and thermodynamic properties of wheat malt under storage conditions

Abstract

The growing use of wheat malt in food applications has boosted studies regarding suitable conditions for processing and storage. Because water sorption during storage may affect the malt functionality, sorption isotherms of wheat malt were determined aiming at covering a wide range of temperatures (10–40°C) and relative humidity (5.80–98.18%). Different theoretical models were fitted to the experimental data. Thermodynamic properties as heat of sorption, enthalpy, entropy, and Gibbs free energy were evaluated. Equilibrium moisture content tended to increase with increasing water activity and decreasing temperature. Henderson and GAB models showed the best fit for wheat malt isotherms. Isosteric heat of sorption increased as the moisture content decreased. Differential enthalpy (−1,071.82 to −36.95 kJ/kg) and entropy (2.29 to 0.12 kJ/k/K) values were linearly dependent, meeting the requirements to confirm the compensation theory. Water adsorption of wheat malt was considered as an enthalpy‐driven (ΔH < 0) and spontaneous process (−324.13 kJ/kg< ΔG < −0.13 kJ/kg). Reported data can be useful for designing adequate storage conditions of wheat malt. Practical Applications Wheat malt has been widely used together with or in replacement of barley malt in many food applications, from brewing to ingredient industries. As a consequence of the seasonality, wheat malt should be stored for long periods to ensure the supply chain over the year. As seen as the storage conditions may affect the quality and shelf‐life of wheat malt, this work aimed at: reporting experimental conditions to better preserve the malt quality and make viable its long‐term usage in different food applications; determining and evaluating its water sorption properties in a range of temperatures and relative humidity; providing mathematical models and thermodynamic analysis for designing adequate storage conditions.

Biodegradation, Water Sorption Isotherms and Thermodynamic Properties of Extruded Packaging Composed of Cassava Starch With Tomato Peel

“…Thus, the value of (∆Hdiff) at low moisture contents indicates the presence of more active sorption sites, that is, a greater interaction of polymer-water bonds. This behavior has also been described in other materials, such as wheat malt [47], papaya seeds [13] and a bionanocomposite produced from pectin and pracaxi oil [48]. The differential enthalpy curves tended towards higher values as the moisture content increased until they reached a maximum value and stabilized, indicating that the heat of evaporation at this time was the same as the latent heat of vaporization of pure water [49].…”

Moisture sorption isotherms and thermodynamic properties of cowpea (Vigna unguiculate L. Walp) stored in a chamber under controlled humidity and temperature

“…If the Gibbs free energy (ΔG) described as the measurement of the sorbent affinity of water during the sorption process is positive, the energy supply from the environment for the occurrence of the reactions is necessary (McMinn et al, 2005). The phenomenon occurs spontaneously if the Gibbs free energy is negative (Kaleemullah & Kailappan, 2007; Silva et al, 2021). ΔG change with EMC is shown for 35°C during adsorption and desorption (Figure 8).…”

Moisture sorption isotherms of reduced‐sugar confectionery coatings elaborated with stevia: Mathematical modeling and thermodynamic analysis

“…These parameters can be found by fitting Equation ( 7) to the data obtained from Equations ( 4) and ( 6). The validity of Equation ( 7) can be verified by comparing the value of T β to the harmonic mean temperature calculated as T hm ¼ n= In that case, it could be inferred that the adsorption process is driven by ΔH s when T β > T hm and driven by ΔS s when T β < T hm (Silva et al, 2021). The application and validity of the enthalpy-entropy compensation theory was tested by fitting Equation ( 7) to the calculated values of ΔH s and ΔS s from the experimental adsorption isotherms.…”

“…The , henceforth called sorption entropy, can be related to the number of available adsorption sites and calculated from through the following expression (Silva et al, 2021): …”

“…Then, the ΔH s crosses zero, indicating that the condensation heat of adsorbed water (Q s ) is similar to the condensation heat of pure water (ΔH v ). In this zone, the water molecules in the material behave as the molecules in the liquid state (Silva et al, 2021).…”