Several variables have been studied in four factorial experiments in order to determine their influence on the rate of de-tinning of cans containing tomato products, as follows: net weight; filling temperature; initial nitrate content; Brix value; pH; tinplate steel annealing; body corrugations; exposed steel; and some anions.Nitrates and net weight (i.e. residual internal air) were found to be the major factors influencing de-tinning; also, their effects were found to be independent and additive. In 500 g cans stored at 20uC for 24 months, the increase of dissolved tin is proportional to nitrates and the net weight according to the estimated ratios:and Technological considerations about the importance of Brix are discussed, and the predicted distributions of dissolved tin after 24 months are calculated for a simulated batch of 100 000 cans. According this model, the levels of 150, 200, 250 mg kg 21 of tin content would be exceeded by 64%, 25%, and 4%, respectively, of cans filled with high Brix tomato products (6 . 5uBx); in the case of the less aggressive 'natural Brix' products (5 . 0uBx), the same levels of tin content would be exceeded by 42%, 6%, and 0 . 5% of the cans. CEST/2030
Ketchup flow properties were investigated with a concentric cylinder viscometer in the temperature range .from 30°C to 80°C. A partial characterization of the product viscoelastic behavior at 30°C was also made by "Strain test" and "Frequency test. " The Harper and El Sahrigi equation (7" = acJ eEdRT), as well as the equation that links the apparent viscosity of ketchups to the serum viscosity and to the pulp content (% = qserum +A(%PJB), do not describe adequately the ketchup flow behavior that we found to be highly affected by the production technology and by the raw materials used.
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.
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