Discussion summary: Papers by van Weerden, Shacklady, and Bressani

Asked about the meaning of the term "technological quality" of proteins, Dr. 8ressani replied that the phrase was used to indicate how amenable (or otherwise) protein preparations are to normal domestic or industrial processing. It was recommended that new preparations should be evaluated in terms of their replacement for other protein sources rather than in absolute terms. This is, in fact, the normal procedure when evaluating food mixtures for human consumption.

Senez, commenting upon van Weerden's paper, pointed out that the rations containing yeast in the experiments he described were generally supplemented with methionine. With regard to the apparent differences in species response to the fungus tested, he wished to stress that it related to only one out of several thousands of fungi that might be used. van Weerden agreed with both comments, but said that the latter served to underline his contention that we know very little about this very large subject.

Stanton commented upon the one in one million level of risk mentioned by Shacklady and said this was close to the natural frequency of mutation of many bacteria. He also suggested that Tetrahymena pyriformis could be a useful organism for field-workers comparing or evaluating potential feed ingredients. In reply, Shacklady said that the one in one million possibility of error referred, not to mutagenicity studies, but to lifespan feeding studies on experimental animals, and simply indicated the magnitude of the studies acceptable to the FDA Regarding T. pyriformis, this has been used by some workers as an index of protein quality, but it has a number of disadvantages, one being that it does not have an absolute requirement for lysine, frequently the first limiting amino acid in cereals. As far as Shacklady knows, it has not been used in mutagenicity studies, the most commonly used organisms being Salmonella typhimurium mutants along with those of Escherichia cold and Bacillus subtilis.