Retention of the quality of blackcurrant juice in lacquered tinplate cans

Authors

• Jarl Häggman The State Institute for Technical Research, Laboratory for Food Research and Technology, Helsinki
• Taina Kuusi The State Institute for Technical Research, Laboratory for Food Research and Technology, Helsinki

DOI: https://doi.org/10.23986/afsci.71597

Abstract

In planning the marketing of blackcurrant juice, a material which has been studied in our laboratory for years (cf. 7, 8, 9), it is important to find a favourable solution to the problems arising with respect to storage and transport containers. The materials most commonly used today for this purpose, glass and plastic, have certain disadvantages, viz. the fragility and weight of glass, and the aroma loss which often occurs in plastic containers. Particularly in cases of long-distance transport, such as in exportation, the question of the most suitable packaging of the juice still presents a problem. Experience of the tinplate can is very limited in this respect. Its mechanical properties are well suited for the purpose, but its chemical suitability is less certain. Tinplate, which is tinned steel plate, is corroded by acid products, especially in the presence of free oxygen, and this may have results which are fatal both to the quality of the product and to the can. Corrosion may be prevented by using cans coated inside with acid-fast lacquers, but in practice the product does, nevertheless, generally come into direct contact with the metal at the sites of scratches and pores in the lacquer film. In addition to acids, blackcurrant juice contains also an ample measure of colouring matters of the anthocyan type; these combine with tin ions, dissolved by the acids from the plate, forming unpleasant looking insoluble compounds. Iron dissolved in the content of the can may also induce colour changes in the anthocyans. The practical purpose of the present study is to settle the question of whether lacquered tinplate cans are suitable for the storage of blackcurrant juice, and to determine the importance of the effect of scratches in the lacquer film on the quality of the juice.