Measuring the Deliquescence Point of Crystalline Sucrose as a Function of Temperature Using a New Automatic Isotherm Generator

Figures & data

Figure 1 Schematic diagram of the interaction of a crystalline solid, such as sucrose, with water vapor in the atmosphere at various relative humility values, where RH_E = environmental relative humidity and RH_o = critical relative humidity. Stages A through D are explained in the text (color figure available online).

Figure 2 Gibbs free energy of a solid and its aqueous solution as a function of %RH. The %RH at which the solid and the solution Gibbs free energies become equal is the deliquescence point (DRH or RH_o ) (excerpted from reference 2).

Table 1 Saturation solubility data for sucrose in water in both g sucrose per g water and %MC (dry basis) units as a function of temperature from Bubník and Kadlec.[28]

Temperature (°C)	Sucrose (g) per water (g)	%MC (db)
15	1.9443	51.432
20	2.0047	49.883
25	2.0741	48.214
30	2.1535	46.436
35	2.2435	44.573

Figure 3 Crystalline sucrose DDIs obtained using a 300 mL/min flow rate and saturated sucrose solution values (moisture content values from Table 1 and a_w values from this study [Table 2]) at 15, 25, and 35°C.

Table 2 Saturated sucrose solution a _w and deliquescence point (RH _o ) values of crystalline sucrose at 15, 25, and 35°C

		RHo values for four methods				Literature values
Temp. (°C)	aw  × 100	Linear extrapolation	RH after the MC step change	Savitzky-Golay	Yuan and others	aw  × 100	RHo	References
15	86.2 ± 0.20^a	85.9 ± 0.40^a	86.3 ± 0.10^a	86.3 ± 0.00^a	86.3 ± 0.20^a
25	84.8 ± 0.80^a	85.7 ± 0.10^a	85.8 ± 0.00^a	85.6 ± 0.07^a	85.9 ± 0.10^a	85.0	85.0	Salameh and others[8]
						84.3		Van Campen and others[29]
							84.4	Rüegg and Blanc[30]
35	84.4 ± 0.20^a	84.0 ± 0.10^b	84.0 ± 0.10^b	84.0 ± 0.07^b	84.0 ± 0.10^b
The RHo values were obtained using four different methods as explained in the Materials and Methods section.
Means with the same letter within a row (difference among measurement methods and the saturated solution aw at a given temperature) are not significantly different at p = 0.05.

Table 3 Calculated RH_o values at 15 and 35°C using Eq. (2) compared to extrapolated RH_o values (Table 2). The solubility of sucrose in mol/mol (n) was calculated using the solubility data in Table 1

Temperature (°C)	Solubility of sucrose, n (mol/mol)	Linear extrapolation RHo	Calculated RHo
15	0.10233	85.9	86.5
25	0.10916	85.7 ^a	—
35	0.11334	84.0	84.9
^aValue used to calculate RHo values at 15 and 35°C.

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