A study was designed to compare the Kjel-Foss automated macro-Kjeldahl method and a block digestion- steam distillation method. The official AOAC Kjeldahl method was used as a reference procedure. Six products with a crude protein range of 10-30% were analyzed by 23 laboratories. Five laboratories analyzed the samples by the official AOAC method, 8 laboratories used the automated Kjel-Foss method, and 11 laboratories used the block digestion with steam distillation method. Standard deviations for each product and each method for both repeatability and reproducibility are given. The block digestion- steam distillation method has been adopted official first action.
A study was undertaken to determine whether free chlorine or sulfide anions could yield positive results for the malachite green test in meat samples when sulfite was not present. Malachite green solution was added to a mechanically deboned poultry (MDP) sample spiked with either chlorine or sulfide ions. The presence of chlorine in MDP samples at any concentration tested did not yield a positive reaction for the malachite green test. When sulfide ions were introduced into MDP samples, positive results were observed at 40 μg sulfide ion/g MDP and above. Because aqueous solutions of sulfide at the levels mentioned have a relatively high pH, it was necessary to determine whether the pH or the presence of the sulfide ions had caused this positive reaction to the malachite green test. After a comparison of a solution of sulfide, and a solution of a matching pH, it was observed that the sulfide present caused the positive reaction to the malachite green test.
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