Corrosion Behaviour of Tinplate Cans in Contact with Tomato Purée and Protective (inhibiting) Substances

The dissolution of iron and tin from tinplate cans filled with tomato purée (pH 4.34) and dioctyl sebacate oil (DOS), essential onion oil (EOO) or potassium nitrate was studied using atomic absorption spectroscopy (AAS), while nitrate was determined using high-performance liquid chromatography (HPLC). The maximum values found in cans were up to 284 mg kg(-1) for tin and 513 mg kg(-1) for iron at elevated storage temperature. Results indicated that the addition of EOO to tomato purée prevents the corrosion process in the case of tin, where concentrations were lowered from 223 to 28 mg kg(-1) for cans with DOS oil and EOO at 20 degrees C, respectively (inhibition rate of 87%). On the other hand, the presence of EOO enhanced the corrosion process for iron increasing the concentration from 15 to 46 mg kg(-1) during 7 months of storage, although this value did not exceed maximum permitted value (50 mg kg(-1)). In cans with tomato purée and potassium nitrate, dissolution of tin started after 30 (36 degrees C) and 60 (20 degrees C) days of storage as a consequence of nitrate action, which act as a corrosion accelerator. Since the addition of EOO improves the taste of canned tomato purée, its potential use as a corrosion inhibitor would be of interest.