| Sulfites are commonly used as blanching agents and preservatives in the processing of foods. However, the ingestion of large amounts of sulfites can bring harmful reaction to human health and should be correctly and strictly controlled. The determination of sulfite is not an easy task because of its rapid oxidation to sulfate and different conditions existing in foods. In the present study, the development and validation of an reagent-free ion chromatography method and a capillary electrophoresis method for the determination of sulfites in aquatic products were described. Formaldehyde was chosen as the stabilizer to prevent the oxidation of sulfites. Meanwhile, in order to control the problem of excessive sulfites, we not only established the reliable detection methods, but also did some initial research on non-sulfur preservative additive. Specific results are as follows: 1、An reagent-free ion chromatography method was established for detection of sulfites. The chromatography separation was accomplished by Dionex ICS-1500with suppressed conductivity detector using an AS11-HC anion-exchanged column eluted with potassium hydroxide. The results of stability of sulfite in solution with different stabilizers showed that formaldehyde had the best stabilizing effect. The method validation provided excellent results. The target ion was separated within13minutes and the limit of detection was0.36mg/kg (expressed as SO32-). The method was linear for sulfite concentration ranging from0.2mg/L to40mg/L (correlation coefficient up to0.9997), and the average recoveries was from79.7%to83.5%in shrimp. The precision was satisfying the need of detection with the RSD less than4%.2、The method for the determination of sulfite by CZE-indirect UV detection with formaldehyde as stabilizer was described. Using an electrolyte system containing10mmol/L Tris as the carrier electrolyte,1.5mmol/L pyromellitic (PM) acid as UV-absorbing probe and1mmol/L diethylenetriamine (DETA) as electroosmotic flow modifier. Sulfite was separated within7minutes. The limit of detection of this method was0.55mg/L in solution and5.5mg/kg in sample. Good linearity of quantitative analysis was achieved within0.5-15mg/L. The recoveries from frozen shrimp were73.9%-79.2%. The precision was satisfactory with the RSD less than7%. 3、Ginger, ascorbic acid and phytic acid wre used to provide preservatives for inhibiting the darkening and microbiological growth of Chinese Shrimp(Fenneropenaeus chinensis). Chinese shrimps treated with blend of ginger, ascorbic acid and phytic acid were kept at4℃for7days and the polyphenol oxidase (PPO) activity, pH, total bacterial count (TBC) and sensory scores of the shrimps were periodically measured during storage. The results showed the effect of ascorbic acid was better than phytic acid for inhibiting PPO activity at the same concentration level. Three experimental groups provided active effects on inhibiting the decay of shrimps. Three ginger compounds were20%(w/v) ginger extraction+0.1%phytic acid,20%(w/v) ginger extraction+0.5%ascorbic acid and20%(w/v) ginger extraction+0.1%phytic acid+0.5%ascorbic acid. These three compounds provided a good inhibitory effect against the increasing of pH, prolong the time of reaching the acceptable TBC level by3days,2days and2days, respectively, and prolong the time of reaching the acceptable sensory scores by2days,3days and2days, respectively. In sensory scores aspect, compound containing0.5%ascorbic acid alone showed highest scores than the other two compounds. The results suggest that ginger compounds provide promising effects for delaying the darkening and microbiological growth of Chinese shrimps. |
PDF Full Text Request