TIN BINDING IN CANNED GREEN BEANS

Tin distribution was studied in green beans from detinned cans and in tin-free green bean puree incubated, under nitrogen, with stannous citrate. Tin was determined by colorimetry of a phenylflurorone-Sn4+ complex. Canned beans were drained, homogenized, and centrifuged. Approximately 90% of the total tin remained in the drained beans. Ninety percent of this tin was recovered in the centrifugation sediment (up to 21 mg of tin/g dry weight) and could not be extracted from it by acid, alkaline, or saline solutions. Ethylenediaminetetraacetic (0.2 M) and 0.05 M cysteine solutions released respectively 39 and 30% of this bound tin. Pectinases plus cellulases, or α-amylase plus glucoamylase, released no tin; proteases released up to 13%. The model system yielded similar results. In both cases, stannous ions appear to be strongly bound to insoluble bean constituents otherwise than by electrostatic attraction or physical adsorption. Such bindings may account for the absence of toxicity of tin in solid canned foods. © 1979, American Chemical Society. All rights reserved.