Abstract
It is well known that canned asparagus dissolves tin from uncoated inner surface of the can in the short term of storage after manufactured, however the cause of this phenomenon has not been known. The present paper deals with the internal corrosion of canned asparagus and its correlation to the tin dissolving activity of cystine, cysteine and asparagus.
Extract of asparagus freeze-dried and stored at room temperature for 0-3 years was subjected to the test packing in baby-food cans. Closed cans were sterilized at 120°C for 20 minutes and stored at 38°C.
The corrosion factors were easily extracted with boiling methanol. They are inactive against cation exchange resin and stable in the acid medium but considerably unstable against alkaline solution. Thus, the action of detinning of four sulfur containing amino acids and relative substance were examined. When more than 500ppm of cystine is contained in the packed can, severe corrosion and sulfur stain was accelerated. Dried asparagus contained more than 15000ppm of cystine+cysteine.
The influence of oxygen or nitrogen substitution in the reaction medium were studied in the conection with the detinning action of cystine and cysteine. Cystine accelerated severe corrosion in the absence of oxygen, but cysteine promoted severe corrosion only at the presence of oxygen. Cystine and cysteine are assumed to be the factors which play one of the main roles in the proceeding of the corrosion in canned asparagus.
