Recent case histories of food product -metal container interactions using scanning electron microscopy-x-ray microanalysis

Abstract

Scanning electron microscopy (SEM) and x-ray microanalysis (EDS) were used to investigate stress corrosion cracking (SCC) in plain tinplate food cans, product discoloration, filiform corrosion, pitting/perforation corrosion, and loss of coating adhesion in enameled food cans. Intergranular SCC of uncoated tinplate occurred in canned pineapple juice. This is a rare occurrence in acid food products. The fracture developed in the can headspace only at the product line/metal interface by an interaction of the detinned metal surface with stress-inducing compounds in the product. Black discoloration of rice granules in the can headspace of a chicken and rice product was caused by the formation of metal sulfides. The source of the metal contamination was traced to metallic dirt in the coating on the tin- free steel end. Blackening of light tan-colored olives and brine occurred after 1 year of storage in enameled tinplate containers as a result of pitting corrosion at the side seam weld. The cause of the pitting was a defective side seam stripe which failed to protect the weld. A perforation problem occurred at the score line of aluminum-tinplate bimetallic cans. The failure was caused by the high chloride content of the fruit product Filiform corrosion resulted in perforations that occurred on the outside surfaces of two-piece tin-free steel cans packed with tuna. The cause of the corrosion was related to scratch defects in the exterior coating and the presence of chloride and sulfate cannery residues in the corroded areas. An enamel adhesion failure developed inside two-piece tin-free steel cans that contained mushrooms. Wrinkles in the coating which were introduced during can manufacture were cracked. The fractures were pathways for product-steel interaction which resulted in container failure.