Investigation of folic acid stability in fortified instant Asian noodles by use of capillary electrophoresis

A simple, rapid procedure, using capillary zone electrophoresis (CZE), that can efficiently measure added folic acid in fortified instant fried noodles has been developed and validated. Optimum separation of folic acid was obtained on a 72 cm × 75 μm capillary using 8 mM phosphate-12 mM borate run buffer with 5% MeOH at pH 9.5, temperature of 30 °C and voltage of 28 kV. The extracts were introduced into the capillary via electrokinetic injection and the folic acid monitored at 214 nm. For quantification purposes, nicotinic acid was added as internal standard to all samples. Under these conditions the analysis required approximately 12 min. Good results were obtained for different analytical parameters including linearity, accuracy and precision. The limit of detection was calculated to be 5.3 mg/L. Prior to CZE determination, noodle samples were homogenized in the buffer solution for 1 h followed by treatment with α-amylase solution for 1 h at 65 °C or protease solution for 4 h at 37 °C. The enzyme solution was added at a concentration of 25 mg/L and then adjusted to pH 7.0. Using standard addition to eliminate the effect of sample matrix interference, results showed that a higher and more efficient recovery of added folic acid could be obtained when using α-amylase. During the four main stages of instant fried noodle manufacturing (dough crumbs, cut sheets, steaming and frying) folic acid was found to be stable with recoveries of 96–103%.