HPLC determination of stability and distribution of added folic acid and some endogenous folates during breadmaking

Bread flour was spiked with folic acid (1.40 mg/Ib or 3.08 mug/g of flour) and processed into bread by the sponge and dough method. Changes that occurred to added folic acid and endogenous folate contents through different processing stages, including sponge formation, proofing, and baking, were assessed by reversed-phase ion-pair HPLC combined with UV and fluorometric detection. Sample extraction required alpha -amylase and rat plasma deconjugase digestion, and sample preparation required purification by solid-phase extraction. Added folic acid was measured by monitoring UV absorption at 280 nm. Four selected forms of endogenous folates including tetrahydrofolate (THF), 5-formyl-THF, 10-formylfolate, and 5-methyl-THF were identified and quantified throughout the bread processing using a fluorescence excitation wavelength of 290 nm and emission wavelength of 350 or 450 nm. Data indicate a relatively good stability of added folic acid and native folates to the baking process, and increased endogenous folate contents in dough and bread as compared with the flour from which they were made.