かん詰の内面腐食に関する研究

III. ミカンかん詰のスズ溶出量に及ぼす硝酸イオンの影響

抄録

Further studies were made on effects of nitrate on dissolving of tin from an internal surface of can containing acid products.
In order to investigate the behavior of nitrate contained in syrup for use in canned fruits, a canning experiment test of mandarin orange was conducted, using syrups containing various amounts of nitrate. Syrups in general for use in canned fruits contain rather a small amount of water (18%), so-called preparing water, in comparison with syrups intended for use in canned soft drinks. In this case, they contain water at the mate of 63%.
With the increase of the amount of nitrate added to the syrup, the rate of detinning increased in the early stage of its storage (within 3 months). No significant changes regarding vacuum level, pH, organoleptic quality, etc. were found in the samples containing nitrate, indicating that nitrate attacked the metal directly without accompanying any reaction with the content.
Water samples from wells of canning plants in a certain district of Japan were found to contain significant amounts of nitrate. It is recommended from the above results that the preparing water ought to be checked as for its nitrate content, and that water containing less than 5ppm of nitrate-nitrogen can be used for preparing the syrups.