• deliquescence;
  • critical relative humidity;
  • water activity;
  • sorption;
  • mixtures

ABSTRACT Many common food ingredients (crystalline sugars, inorganic salts, and organic acids) exhibit deliquescence, a moisture-induced solid to solution phase transition that occurs at a characteristic relative humidity, RH0. An automated gravimetric water vapor sorption balance was used to measure RH0, and a water activity (aW) meter was used to measure aW of saturated solutions to characterize deliquescence of individual food ingredients and their mixtures. Measured RH0 and aW values were similar (P > 0.01), except for ingredients that form hydrates (confirmed by FT-Raman spectroscopy) and for mixtures containing more than 2 ingredients. A significantly lower (P < 0.01) RH0 was obtained for all mixtures compared with individual ingredients, and optical microscopy images demonstrated the impact of ingredient contact on RH0 lowering. Increasing temperature significantly decreased RH0 (P < 0.01). Results demonstrate that deliquescence lowering in ingredient mixtures has the potential to impact both chemical (for example, sucrose and citric acid mixtures) and physical stability (caking) of powdered ingredient mixtures.