Basic Principles of Corrosion of Food Metal Packaging

Abstract

The corrosion of metal packs is of major importance for health reasons and with reference to the possible reduction of shelf-life values. Basically, main failures of metal packages can be excessive metal amounts in food products, hydrogen swelling, perforation, lacquer blistering or delaminating, and modification of sensorial properties. Therefore, the possibility of minimising corrosion phenomena is of great concern depending on the exact knowledge of chemical and physical factors and causes. This chapter examines the thermodynamic and kinetic aspects of the corrosion mechanisms of tinplate, tin-free steel (TFS) and aluminium with a brief introduction to corrosion theory. In detail, a description of main anodic, cathodic and galvanic coupling prevailing reactions is provided in this chapter with particular reference to preserved foods and possible consequences (aggressiveness). The following factors with some correlation with corrosive phenomena are considered: chemistry of the metallic material, food formulation, packaging process, properties of the organic coating, and shape and capacity of the container. In particular, the role of oxygen is discussed. In addition, the description of the corrosion morphology is shown along with some practical examples with reference to failures such as detinning and pitting.

Criteria and methodologies for determining the causes of swelling of canned tomatoes in tinplate containers

“…The more or less conspicuous swelling of tomato cans, which is an index of the product alteration, may usually depend on physical–chemical phenomena of de‐tinning corrosion of the container with the development of hydrogen and swelling of the can (Barbieri et al., 1971; Benitez et al., 2006; Dhuey, 2019; Montanari, 2015; Palmieri et al., 2002; 2004; Sherlock & Britton, 1973). The alteration of canned tomatoes is indeed one of the main causes of litigation among industries that produce the tinplate containers and those that produce canned food starting from raw material.…”

“…The study of the mechanisms involved is therefore of considerable practical interest. When canned in uncoated tinplate containers, the tomato derivatives create an environment that determines the inversion of the electric tin reduction potential standards of the Sn/Fe pair (Montanari, 2015), thus corroding, albeit slowly, the tin of the metal base. Corrosion begins only when the tin has almost completely oxidized in the product.…”

“…and high aggressiveness (sauerkraut, asparagus). This is due to the presence of sulfur compounds, some of which, such as the amino acid cysteine, are also present in tomatoes (Chang et al., 2022), or of sulfoprotein compounds such as those present in fish products, meats, legumes, and also in corn to mask the marbling that forms on traditional tinplate (Barbieri & Rosso, 1990; Montanari, 2015). For these reasons, the use of coated cans has been continuously increasing.…”

“…In coated cans, the protection is given, firstly, by the coating (organic protection) and, secondly, by the underlying tin covering, which provides further physical protection by separating the tinplate from the product through an electrochemical protection for corrosion. In these cans, corrosion develops from under‐film de‐wetting, limited to points where the porosity of the coating allows direct contact between the product and the metal ending with the oxidation of the iron which begins when the steel is no longer protected (Montanari, 2015; Simal ‐ Gándara, 1999).…”

Food‐packaging interactions investigated by electrochemical impedance spectroscopy

“…Metallic packages are an impermeable barrier for light and oxygen, preventing the degradation of the food product. However, due to metals susceptibility to corrosion, metallic packages are internally coated with a polymeric film whose main aim is to protect both metal and food product by their mutual attack (Abramowicz et al, ; Magami, Oldring, Castle, & Guthrie, ; Montanari, ). Most metallic packages are coated on both sides, the external coating being necessary to provide protection from the environmental factors and to offer the support for decoration and consumer information (Oldring & Nehring, ; Salas, Wiener, Stoytcheva, Zlatev, & Beltran, ).…”