Katarina Berković

Corrosion inhibition with different protective layers in tinplate cans for food preservation.

BACKGROUND In this work the influence of essential onion oil (EOO) on the protection of tinplates was compared with dioctyl sebacate oil (DOS) and epoxy phenolic lacquers, which are frequently used in the food canning industry. RESULTS When EOO as the protective layer instead of DOS oil was used, tinplate porosity, measured electrochemically (7.58 ± 1.97 µA cm(-2) and 23.0 ± 1.3 µA cm(-2), respectively), and iron coating mass, calculated from AAS data (1.52 ± 0.15 mg m(-2) and 3.14 ± 0.42, respectively), was much lower indicating better corrosion protection. At higher storing temperature (36 °C) the addition of EOO to canned tomato purée enhanced the formation of hydrogen with time. The increasing volume fraction of H(2) (from 34.0 to 90.9% for cans without nitrates, and from 33.8 to 89.2% for cans with nitrates) is an indicator that corrosion takes place. CONCLUSION As the use of EOO improves the protection of tinplate compared with DOS oil, and is almost as effective as epoxy phenolic lacquer, the addition of EOO can be recommended due to lower cost of canned food production and enhanced organoleptic properties, but the storage temperature has to be lower then 36 °C.

Reduction mechanism of 3-hydroxy-4-hydroxyiminomethyl-5-hydroxymethyl-1,2-dimethylpyridinium iodide in an acidic medium

The reduction mechanism of the selected oxime, 3-hydroxy-4-hydroxyiminomethyl-5-hydroxymethyl-1,2-dimethylpyridinium iodide (HS10), has been studied by normal pulse polarography (NPP) from a Britton—Robinson buffer of pH 2.6, predominantly on a static mercury drop electrode (SMDE). At pH 2.6, 99% of HS10 is present in the undissociated hydrophobic form. The limiting reduction current is diffusion controlled (diffusion coefficient D = 1.5 × 10 −6 cm2/s; half-wave potential E12 = −0.355 V vs. Ag/AgCl/KCl(sat) reference electrode). The NPP wave of HS10 at pH 2.6 has the characteristic features of a reduction complicated by reactant adsorption. The reduction process is totally irreversible; the average an = 0.975. Considering the uptake of 4e− during the reductive cleavage of the azomethine group (CN) the estimated cathodic transfer coefficient a = 0.234. During the prepulse period t0 the reactant adsorbs at the mercury electrode, following the linear Henry type of isotherm. For 1.01, 4.05 and 8.10 × 10−5 mol 1−1 bulk concentrations of HS10, the surface excesses. Γ0 on SMDE at t = t0 are 0.5, 2.1 and 5.8 × 10−11 mol cm−2 respectively. For the same concentrations of HS10, according to the Henry isotherm the adsorption constant K has been calculated as 4.9, 5.2 and 7.2 × 10−4 cm, which indicates weak reactant adsorption during the pre-pulse period t0.