A voltammetric approach to an estimate of metal release from tinplate promoted by ligands present in canned vegetables

Abstract

A linear sweep voltammetric (LSV) approach is proposed for achieving rapid information on metal release from tinned containers into preserved vegetables. Chopped tomato and pea preserves were chosen as prototypes for acid and nearly neutral canned food, respectively. Metal release in these vegetables tinned into both bare and lacquered containers was compared with that found in synthetic samples containing some organic complexing agents (acetic, ascorbic, citric, malic, oxalic, pyroglutamic acids) present in the vegetables considered, thus showing that some of these components affected markedly the metal release in bare cans. These ligands were concomitantly found to also affect LSV profiles recorded in parallel at Sn and Fe electrodes in synthetic samples, causing the starting potential for their oxidation to be lower, the higher the ligand activity of the species considered. The data indicated that metal release and starting potentials for metal discharge are strictly related, so that LSV is able to provide rapid and useful information on the nature of the protective effect (electrochemical or physical) of tin on the steel underlayer, as well as on the extent of Sn and Fe release.

Migration of iron, lead, cadmium and tin from tinplate-coated cans into chickpeas

“…In terms of quality, related to the migration of metallic trace elements, it can be stated that cans of brand C seem to have the best quality followed by brands B and A. According to our observations, these differences can be related to three causes: the quality of the internal organic coating (the three types of cans have different types of internal coating with different thicknesses), the free internal volume (brand A > B > C) and the composition of the brine (brand A cans contain citric acid which enhances corrosion; Toniolo et al 2009). …”

“…The similarity in the evolution between cans stored at RT, refrigerated and in the oven shows that temperature has a small effect on the release of Fe. In fact, the release of Fe may be due to the fact that chickpeas have a slightly acidic pH (5.08 ± 0.02) which promotes the release of the considered metal (Toniolo et al 2009). …”

New Ultrasound-Assisted Extraction Sample Preparation Procedure for the Fast Determination of Total Sn in Canned Tomatoes by HG-ICP OES

“…Therefore, the resin/polymer coating (lacquering) of the inside of the tinplate of the can is now a common way to protect food from metal contact and to prevent corrosion, especially the subsequent release of Sn from cans and the contamination of the canned food [2,9,10]. In practice, the tinplate deterioration processes are complex and different parameters affect the internal corrosion rate, e.g., thermal treatment, tinplate variables (impurities and surface defects), the acidity of food, the contact time between the food and the packaging, the food water content, the presence of additives or oxidizing reagents, the presence of air (oxygen) in the headspace, and the storage conditions (time and temperature) [6,[10][11][12][13]. Despite these considerations, it can be said that human exposure to Sn has a dietary origin, particularly from the consumption of canned food [14,15].…”

Polarity Reversal of Iron and Tin in Aqueous Malic Acid

“…Polarity reversal occurs in the presence of organic acids (carboxylic) which form stable complexes (SnL) with Sn 2+ and/or Sn 4+ ions (3) causing the dissolution of tin, referred to as detinning. The sacrificial dissolution of tin from plain cans is important in protecting the underlying steel from anodic attack and penetration (4). It also allows the cathodic 'scavenging' of oxygen from the can contents without the appearance of iron corrosion products and/or discolored fruit and vegetables.…”