It should be stressed that no amount of preclinical testing in experimental and farm animals can eliminate the possibility of intolerance when an SCP pro- duct is fed to human subjects. Animal trials can eliminate true toxicity and make human trials ethical, but they c a ~ o t predict the frequency of allergic reactions of a gastrointestinal or cutaneous nature at an unacceptably high level of frequency or severity. Even for subjects who have experienced an allergic reaction neither skin tests with extracts of the material fed nor the radio immune test (RIST) for circulating antibodies to the test material have not thus far yielded consistent or useful results. However, it has proved possible to screen processing variants by incubating extracts of them with cultures of lym- phocytes taken from in&viduals showing such allergic response to the original material. As mentioned above a Candida utilis grown on beet molasses and RNA reduced at €30'~ caused a h g h ffequency of s h n reactions of an apparently allergic nature in human subjects. Not only did an extract of this material stimulate the replication of lymphocytes from reacting individuals but also it was possible to fractionate the extract and demonstrate that the response was due to a protein with a molecular weight of approximately 55,000 Daltons. RNA reduction at 140' eliminated both the in vitro and in. vivo response. One limita- tion to this technique is that the responsiveness of the lymphocytes is gradually lost after a few months. Since then in & f r o lymphocyte response to the methanol grown yeast preparation mentioned previously was assessed by the lymphocyte transformation test ( L T ) . The test gave positive results in sensitive subjects, which were two or more-fold higher than those in age-matched control subjects. The effect was specific and reproducible provided the tests were con- ducted with (i) subjects who were sensitized not more than three months ago and (ii) control subjects did not have a positive LIT response to Moniha antigen, in whch case there would be a cross LTT response with the methanol-grown yeast. Because of its specficity, the L T can be considered a useful aid in diag- nosis of human allegic response to consumption of the methanol-grown yeast.
When applied to provide an in viho in&cation of potential allergenicity in industrially modified preparations of the methanol-grown yeast, the LTT success- fully identified heat shock at an acidic pH as a process that could attenuate the factor(s) responsible for gastrointestinal symptoms. We have since further refined this method and are applylng it to additional SCP products that have caused apparently allergic reactions.
In -F
Selected yeasts, bacteria and fillamentous microfungi can be used as significant protein sources in human diets but processing to reduce their RNA content is required when they are to be used in the quantities necessary for t h s purpos- Allergic responses have not been described with fillamentous micro- fungi but have proved common with yeasts and bacteria. Fortunately t h s prob- lem can usually be overcome by suitable processing. Although thus far experi- mental animals have proved of no value in detecting potential allergenicity for humans, lymphocytes of sensitized in&viduals can be used to screen processing
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USE OF NON-CONVENTIONAL PROTEIN IN FOOD PROCESSING