Copper, zinc, tin and lead in canned evaporated milk, produced in Lithuania: the initial content and its change at storage

Abstract

The study has been carried out to elucidate what contents of heavy metals were typical for canned milk products—evaporated (TS 25.5–28.5%) sterilized milk and condensed sweetened milk, produced in Lithuania in the period 1983–1997. The influence of storage time upon the level of Sn, Pb, Cu and Zn in the products has also been determined. The results show that the most considerable changes occurred in Cu concentration, which gradually decreased from the maximum level in 1983–1985 (2.23±0.18mg/kg) to the minimum level in the latest years (0.44±0.01 mg/kg). Such variation of copper content in canned milks can be closely connected with its changes in raw milk. Zinc content in canned milk products also was in good agreement with raw milk. The content of tin and lead in the canned products many times exceeded their concentration in raw milk and ranged from 28±2 and 0.093±0.005 to 114±4 and 0.29±0.01 mg/kg, respectively. It has been determined that the dependence of the concentration of tin and lead on the storage time of concentrated (or evaporated) sterilized milk is nearest to the parabolic, and in sweetened condensed milk to the exponential function, whereas the small increase of copper and zinc concentrations can be described by straight-line function. The functional dependence obtained enables one to predict the Sn and Pb level in canned evaporated milk products after storage and to foresee the safe initial concentration of these metals in freshly produced evaporated milk, assigned for storage.