Common-ion effects on the deliquescence lowering of crystalline ingredient blends

• Diminished deliquescence lowering occurs in ingredient blends with a common ion.
• The common-ion effect decreases ingredient solubility thereby increasing RH0mix.
• A modified Ross equation improves RH0mix predictions for blends with a common ion.

Deliquescence points (RH0, RH0mix) of ionic crystalline food ingredients and blends thereof were determined using water activity and moisture sorption techniques. Measured RH0mix values of ingredient blends with and without a common ion were compared to Ross equation predictions of deliquescence lowering. In binary blends with no common ion, measured RH0mix values ranged from 5% RH lower to 6% RH higher than predicted; however, when a common ion was present, the measured RH0mix was consistently 6–8% RH higher than predicted. In tertiary blends with a common ion, RH0mix values were 15–18% RH higher than predicted. The higher RH0mix in blends with a common ion is caused by counterion dissociation competition from the common ion. At equilibrium, these solutions will have fewer solutes and a greater vapor pressure than assumed by the Ross equation. A modified Ross equation was developed to compensate for the common-ion effect and improve RH0mix predictions.