Moisture sorption isotherms of raw and extruded wholemeal sorghum flours studied by the dynamic and salt slurry methods

Abstract

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 slurry and dynamic methods, respectively). For the sorghum extrudates, the equilibrium moisture values were higher using the dynamic method, which could be related to the low diffusion coefficient of the material (order of 10 -10). The authors suggest the use of the dynamic method as a better alternative to the saturated salt method in order to determine the sorption isotherms of whole grain sorghum-based food materials.

Moisture sorption behavior and thermodynamic properties of dry‐crystallizedPalada payasam(rice flakes milk pudding) mix determined using the dynamic vapor sorption method

“…Galdeano et al. (2018) studied the MSI of raw and extruded wholemeal sorghum flours by using both isopiestic and DVS methods and concluded very close agreement in the results obtained by both the methods for both the products. They reported that the experimentation time of 30 days in case of the static method was reduced to 30 hr using the DVS method.…”

Physical–chemical evaluation of flours from brewery and macauba residues and their uses in the elaboration of cookies

“…According to the European Pharmacopoeia classification, MC flour was categorized as a highly hygroscopic material due to its adsorption higher than 15% (w/w) at 25°C, meanwhile, MS and PM were considered as moderately hygroscopic as they reached adsorption values from 2% to 15% at a w = 0.80 at 25°C. due to its typical intermediate moisture (Brunauer et al, 1940;Chen et al, 2017;Galdeano et al, 2018) and is characteristic for nonporous materials or with pores that range from mesopores to macropores. The first inflection point of the isotherm, concave on the a w axis, represents the formation of the monolayer adsorbed on the surface, while the second point, convex on the a w axis, characterizes the adsorption of multiple layers on the surface (Gili et al, 2017;Rahman, 2009).…”

DESORPTION ISOTHERMS OF GRAIN SORGHUM (Sorghum bicolor [L.] Moench) FLOUR

“…The sorption isotherm describes the amount of water sorbed (adsorption or desorption) at equilibrium by a material with known water activity (Aw), constant temperature, and constant pressure (Galdeano et al, 2018).…”