Abstract
Water activity (aw) was measured for various two component aqueous solutions at various inter-solute interactions and the observed aw was compared with the theoretical prediction by Ross equation assuming no inter-solute interactions. For solutions with neutral components including electrolytes, sugars, and neutral amino acid, solute-solute interaction was weak so that no substantial deviation was observed for observed aw from that predicted by Ross equation. When acid and base were involved, the deviation between the two was large because of the neutralization. For a solution containing macromolecule, bovine serum albumin (BSA) and sucrose mixture showed a strong cooperative effect between solutes to reduce aw much smaller than the theoretical expectation. In a case with an amino-carbonyl reaction between glycine and ribose kept at 60℃, a drastic increase in optical absorbance at 327 nm was observed with time and aw increased accordingly because of the water liberation at the initial stage of the Schiff-base formation and the following complex Maillard reaction process to reduce the number of solute molecules in the system.
