An experimental study on the scavenging effect of ascorbic acid on iodate ions in simulated gastric juice

Abstract

Objective To explore the conversion rate of iodate ions (IO3-) being reduced to iodide ions (I-) by ascorbic acid (C6H8O6, VC) in simulated human gastric juice, and to provide references for further safety evaluation of edible salt iodized with potassium iodate. Methods An ion chromatography method was developed to detect iodide ions in simulated gastric juice. The conversion rate of iodate ions being reduced to iodide ions was used as the index for scavenging rate of iodate ions. In simulated gastric juice in vitro and in 37 ℃ water bath, the scavenging effects of VC on iodate ions were determined in simulated gastric juice with different VC concentrations and simulated gastric juice acidities, as well as for different reaction time. Ion chromatography column: Dionex IonPac AS19 (250 mm × 4.0 mm); eluent: KOH 30 mmol/L (online produced), isocratic eluting, flow rate 1.0 ml/min, injection volume 100 μl, and detected by a conductivity detector. Results Performance of the method: within the range of 0-5 000 μg/L, iodide ions concentration and the chromatographic peak area had a good linearity (correlation coefficient r= 0.999 7), and the detection limit of iodide ions was 20 μg/L. For quantification of iodide ions in simulated gastric juice, the relative standard deviation (RSD) of repeated measure for 6 times was < 2.0%, the standard addition recovery rate was 97.6%-102.4%, and the overall average recovery rate was 99.4%. In the simulated gastric juice with a pH of 1.4 containing 5 mg/L and ≥10 mg/L VC, the reaction time to achieve 100% conversion rate of iodate ions being reduced to iodide ions was 5 min and 2 min, respectively. In the simulated gastric juice with a pH of 3 containing 10 mg/L ascorbic acid, the reaction time to achieve 100% conversion rate was 15 min. VC quantitatively reduced iodate ions to iodide ions by the stoichiometric relationship between reactants of the reduction reaction equation, and every 100 μg VC quantitatively reduced 24.0 μg of iodine in iodate to iodide ions. Conclusions In simulated gastric juice, the reaction of iodate ions being reduced to iodide ions by VC is a stoichiometric reaction with relatively fast reaction rate, the scavenging rate of iodate ions by VC within the concentration level in human gastric juice can reach 100%. The results prompt that the iodate ions from edible salt iodized with potassium iodate in daily diet are reduced to iodide ions mainly in the human stomach. Key words: Gastric juice; Iodine; Salts; Iodate ions; Ascorbic acid; Conversion rate; Scavenging rate