Abstract
The global production of metal cans is more than 300 billion cans. Benefits of metal packaging consist mainly from the great strenght, excellent barrier properties and good thermal conductivity. The main problem of used metal packaging are the corrosion processes. The corrosion of metal container causes dissolution of tin which is used as a protective layer of the steel shell of the can and other metallic elements used in the manufacture of cans. In this work 31 samples of canned fruit was analysed and the concentration of tin, chromium, cadmium and lead was determined in fruit and in syrup using ICP-OES and ICP-MS techniques. The results showed no difference between the concentration of analysed elements in fruit and in syrup. In none of the analyzed samples the permitted maximum concentration of tin 200 mg.kg-1 was exceeded. Maximum concentration of tin was measured in canned grepfruit (59.8 ±1.9 mg.kg-1). The age of cans had no significant effect on the concentration of tin in canned fruit. The concentration of tin in fruit packaged in cans with protective layer of lacquer was significantly lower than the concentration of tin in fruit packaged in cans without protective layer of lacquer. Concentration of chromium, cadmium and lead in the analysed samples was very low at the natural levels of occurrence of these metals in fruit and it was impossible to determine unequivocally that the measured concentrations of these metals in canned fruit originate from the corrosion of can. The corrosion of the tinplate was studied using scanning electron microscopy with an energy dispersive spectrometer. By analyzing the SEM pictures and EDS spectra, critical areas of tin plate corrosion were observed. Based on the measured results it can be concluded that the consumption of fresh canned fruit is not a major problem for the inhabitants of the Czech Republic in terms of intake of potentially hazardous metals.
Highlights
Metals are one of the most important packaging materials in food industry besides of plastics and paper
Concentration of chromium, cadmium and lead in the analysed samples was very low at the natural levels of occurrence of these metals in fruit and it was impossible to determine unequivocally that the measured concentrations of these metals in canned fruit originate from the corrosion of can
The concentration of tin in fruit packaged in cans with a protective layer of lacquer was statistically significantly different in comparison to the fruit packaged in tinned cans without protective layer of lacquer (F = 37.696 >F c = 4.149)
Summary
Metals are one of the most important packaging materials in food industry besides of plastics and paper. The protective tin coating prevents damage to the packaging it causes dissolution of tin and other metallic elements such as zinc, chromium, lead and cadmium to the inner contents of cans. The increase of these metals content in canned food poses a hazard of a chemical type. From this reason, in the European Union a limit of 200 mg.kg-1 of tin in canned food must be followed by food manufacturers (Council Directive 1881/2006/EC, 2006) amended by Commission regulation 629/2008/EC, 2008). The maximum allowable concentration of cadmium in fruits and vegetables is 0.05 mg.kg-1
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