Investigation of corrosion and container integrity in metal food containers using scanning electron microscopy-X-ray microanalysis

Scanning electron microscopy and x-ray microanalysis were used to investigate microleakage, two incidences of loss of coating integrity, filiform corrosion, and sulfide black corrosion in enamel-lined metal food containers. Microleakage developed in a canned cheese sauce at the side seam weld and was traced to a hot weld and a cold weld defect. An enamel-blistering problem developed in an aseptically processed milk-based product when the tinplate was heated above its melting point; the tin melted under the enamel coating, causing the blistering. An enamel-blistering problem, due to silicon contamination of the metal surface prior to enameling, developed on the bottom of a two-piece can that contained a chicken-based product. A sulfide black problem developed in canned clams, caused by scratches in the coating that were introduced during can manufacturing. A filiform corrosion problem developed on the outside of the easy score line of enameled tinplate lids with a light tin coating 0.08 microns thick.     

Investigation of foreign substances in food using scanning electron microscopy-x-ray microanalysis

Scanning electron microscopy (SEM) and x-ray microanalysis (EDS) were used to conduct forensic investigations on metal and glass foreign objects. SEM-EDS is an excellent method for identifying metal foreign objects in food, such as wire, dental fillings, bone, and metal packaging, based on their element composition. From a determination of the extent of corrosion of a metal foreign object using SEM-EDS, it is sometimes possible to determine whether the material has been processed with the food product. Case histories of processed aluminum, unprocessed nickel-coated steel, and corrosion resistant stainless steel foreign objects are discussed. A potential product-tampering problem involving a hole defect in a paperboard package was resolved using SEM-EDS. Blue fibers found in the hole were found to contain brass particles from a ball point pen rather than a syringe needle. SEM-EDS has been used to determine the elemental composition of glass foreign objects and is able to distinguish between many types of glass including container, electrical, and bakeware. A case history is presented to show that although container glasses cannot, in general, be distiguished from one another using SEM-ED S, they can be distinguished by trace element semiquantitative spectrograghic analysis. SEM-EDS can be used to distinguish glass-like foreign objects from glass. Case histories of struvite crystals found in salmon and cream of tartar crystals found in grape juice are discussed. Fourier transform infrared (FTIR) identified the cream of tartar crystal as calcium tartrate, and this complemented the calcium, carbon, and oxygen components of the compound found using SEM-EDS.