Comparison Between Water Vapor Sorption Isotherms Obtained Using The New Dynamic Dewpoint Isotherm Method and those Obtained Using The Standard Saturated Salt Slurry Method

Figures & data

Figure 1 Schematic diagram of the AquaSorp Isotherm Generator used to obtain Dynamic Dewpoint isotherms.

Table 1 Average “as is” moisture content and AquaLab measured a_w values and associated standard deviations at 25°C for the materials used in the DES and PEC and the DDI methods.* The average starting DDI a_w values for both adsorption and desorption parts of the working isotherm, estimated by the AquaSorp Isotherm Generator, and associated standard deviations are also listed. Visually observed mold growth for some of the materials in both the DES and PEC chambers is also indicated. No visual mold growth was observed in the DDI method

Material	MC (% wb)	AquaLab aw values (25°C)	Average starting DDI aw values (25°C)	Mold growth in DES and PEC chambers
Dent corn starch	9.2 ± 0.12	0.447 ± 0.001	0.484 ± 0.026	None
Isolated soy protein	3.8 ± 0.06	0.207 ± 0.001	0.290 ± 0.024	DES ≥ 0.843 aw PEC ≥ 0.903 aw
Microcrystalline cellulose	2.3 ± 0.01	0.408 ± 0.002	0.247 ± 0.039	None
Crystalline sucrose	0.04 ± 0.0003	0.290 ± 0.001	0.313 ± 0.202	PEC ≥ 0.903 aw
Corn flakes	3.0 ± 0.06	0.205 ± 0.004	0.376 ± 0.139	DES and PEC ≥ 0.843 aw
*DES method = saturated salt slurry isotherms obtained using desiccator chambers; PEC method = saturated salt slurry isotherms obtained using proximity equilibration cell (PEC) chambers; DDI method = dynamic dewpoint isotherms obtained using an AquaSorp Humidity Generator.

Figure 2 DES, PEC, and DDI isotherms for dent corn starch (color figure available online).

Figure 3 DES, PEC, and DDI isotherms for isolates soy protein. Mold growth a_w limits for DEC and PEC methods are given in Table 1 (color figure available online).

Figure 4 DES, PEC, and DDI isotherms for microcrystalline cellulose (color figure available online).

Figure 5 Informal statistical comparison of one of the working DDIs to the connected upper and lower 99% DES and PEC confidence limits (±0. 506 mc %db) (color figure available online).

Figure 6 DES, PEC, and DDI isotherms for crystalline sucrose. The deliquesce point and the literature saturated sucrose solution a_w (at 25°C from Salameh et al.[20]) and associated moisture content (at 25°C from Bubnick and Zadlec[21]) are indicated on the figure. Mold growth a_w limits for DEC and PEC methods are given in Table 1 (color figure available online).

Figure 7 DES, PEC, and DDI isotherms for corn flakes. Mold growth a_w limits for DEC and PEC methods are given in Table 1 (color figure available online).

Salameh , A.K. , Mauer , L.J. and Taylor , L.S. 2006 . Deliquescence lowering in food ingredient mixtures . Journal of Food Science , 71 ( 1 ) : E10 – E16 .

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Bubnik , Z. and Kadlec , P. 1995 . “ Sucrose solubility ” . In Sucrose Properties and Applications , Edited by: Mathlouthi , M. and Reiser , P. 107 Glasgow : Blackie Academic and Professional . 1995

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