The Effects of Processing and Extraction Conditions on Content, Profile, and Stability of Isoflavones in a Soymilk System

The effect of processing temperature and pH as well as enzyme-assisted extraction on the content and profile of isoflavones in a soymilk system was investigated. Isoflavone content in thermally treated soymilk at pH 7 and pH 9 was determined following a standard solvent extraction or an enzyme-assisted extraction protocol. Upon thermal processing, at both pH 7 and pH 9, significant interconversions were noted, indicated by the observed decrease in malonylglucosides with the concurrent increase in beta-glucosides. Enzyme-assisted extraction resulted in enhanced isoflavone extraction efficiency and revealed significant loss in total isoflavone content upon processing. This observation suggested that protein-isoflavone interactions, which are dependent on the protein structure and isoflavone form, affect isoflavone extractability, leading to underestimation of any loss that might have occurred in previously reported thermal studies. Accurate isoflavone measurements are essential to determine the processing conditions that result in the least loss of the biologically relevant isoflavone content.