MALDI-TOF MS analysis of isoflavones in soy products

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) is a new technique having a number of advantages for food analysis. This study is the first to demonstrate the use of MALDI-TOF MS to identify isoflavones in soy samples. 2',4',6'-Trihydroxyacetophenone (THAP) and 2,5-dihydroxybenzoic acid (DHB) were both good matrices for isoflavones, but DHB was chosen as the best because it worked well for sample extracts, with good spot-to-spot repeatability. Isoflavones were predominantly ionized in a protonated form with a very small amount of sodium or potassium adduct ions. Fragmentation occurred only through loss of glycosidic residues. Daidzin showed more than twice the response of genistin using MALDI-TOF MS. A simple solid phase extraction of isoflavones from soy samples was developed for MALDI-TOF MS analysis. MALDI-TOF MS can provide an isoflavone profile in 2 min and serves as a powerful tool to identify and study processing changes of isoflavones in soy products.