CHARACTERIZATION AND APPLICATION OF PORCINE LIVER ALDEHYDE OXIDASE INTHE OFF-FLAVOR REDUCTION OF SOY PROTEINS

Two enzyme forms of porcine liver aldehyde oxidase (PAC-I and PAO-II) (aldehyde:oxygen oxidoreductase, EC 1.2.3.1) were purified to homogene ity by using affinity chromatography. Both enzyme forms, PAO-I and PAO -II, have similar pI values of 5.8 and molecular masses of 262000 and 25000 Da, respectively. Compared with PAC-II, PAC-I showed greater aff inity for the soy off-flavor-causing aldehydes n-pentanal and n-hexana l. Purified PAO-I was stable between pH 7.1 and 10.7 and at temperatur es up to 45 degrees C. Energy of denaturation for PAO-I (158.1 kJ/mol. K-1) was more than 3-fold higher than the energy of activation (47 kJ/ mol.K-1). Gas chromatography analysis showed that more headspace volat iles were present in the water extract of soy proteins at pH 7.0 than at pH 9.0. The incubation of a soy protein extract and PAO-I reduced t he pentanal and hexanal contents by as much as 90%. The sensory paneli sts perceived lower beany flavor (p < 0.01) of the enzyme-treated soy protein extract than the control.