Removal of soy protein (SP)-bound 2-nonanone by b-cyclodextrin (bCD) was studied using an equilibrium dialysis technique. It was observed that in the presence of bCD, a significant (p \ 0.05) amount of SP-bound 2-nonanone could be removed in a concentration-dependent manner. Up to 94% of SP-bound 2-nonanone was stripped from SP when 6 mM bCD was present in the system. However, in thermodynamic terms, the net standard free energy change for transfer of 2-nonanone from SP to bCD, i.e., DDG SP!bCD , was essentially zero, implying that the apparent equilibrium binding constant for the formation of bCD-2-nonanone complex was essentially same as that for the SP-2-nonanone complex formation in the ternary system. This indicated that stripping-off of 2-nonanone from SP by bCD was driven by the mass action ratio. Based on these results, it is shown that bCD can be used effectively for removing SP-bound off-flavor carbonyl compounds.