No abstract

A method is described for the determination of sulfite levels in food products by flow injection analysis (FIA). The method is based on the decolorization of malachite green by S02, which is isolated from the flowing sample stream by means of a gas diffusion cell. The FIA method has a detection limit in food sample extracts of 0.1 ppm S02 (3 times peak height of blank), which corresponds to 1-10 ppm S02 in a food product, depending on the extraction procedure used. At the 5 ppm SO2 level in a food extract, the precision of replicate injections is ± 1-2%. The method was tested on a variety of both sulfite-treaied and untreated food products and the results compared favorably with those obtained by the Monier-Williams, colorimetric (pararosaniline), and enzymatic (sulfite oxidase) methods. The average differences from the FIA results were 19, 11, and 12%, respectively, for those samples (n = 12) above SO ppm S02. At lower levels the results were somewhat more erratic due to inaccuracies of the various methods at low concentrations.

An additional collaborative study on the identification of canned salmon species, based on the method and key published earlier, was conducted in 1971. All of the 8 collaborators were able to find usable and intact scales for mounting and identification. The overall percent correct identifications for 48 samples for the 8 collaborators was 79%. Three collaborators correctly identified all 6 samples and 3 more had only 1 of 6 samples incorrectly identified. Since the pink species was correctly identified in all cases and the chum species was correctly identified in 9 of 11 samples, the method has been adopted as official first action for the identification of these 2 species. Additional work will be done to eliminate the problems encountered with the sockeye, coho, and chinook species.

A key based on characteristic scale patterns has been developed to distinguish the five species of canned salmon. The scales are simply removed from the fish skin, examined under magnification, and keyed as to species. Nine of ten cans of unknown salmon were correctly identified by laboratory personnel unfamiliar with salmon species. The one error was due to inadequate explanation of terms used in the key. It is recommended that the amended key be subjected to collaborative study.

A modified method and key for the identification of canned salmon species have been subjected to an additional collaborative study. Of 54 samples examined, 11 collaborators accurately identified 10 of 10 samples (100%) of sockeye, 11 of 11 samples (100%) of chum, 11 of 11 samples (100%) of pink, 11 of 11 samples (100%) of coho, and 11 of 11 samples (100%) of chinook. Nine of 11 collaborators were able to find in all samples usable scales with intact clear areas for mounting and identification. Two of the 11 had a minor problem. The improved, modified method and key have been adopted as official first action for the identification of the sockeye, chum, pink, coho, and chinook salmon species to replace method 18.089.