The trypsin inhibitor activity of processed foods can be determined by measuring the loss of activity of added trypsin under standard conditions. Observed values are not usually independent of the degree of inhibition, and averaging over a range of inhibition levels or extrapolation to zero inhibition may not produce a more reliable value. A somewhat modified method is described which has been tested in two laboratories and used for large numbers of different samples on a routine basis; its application and limitations are discussed.

Classical immunoanalytical techniques are based on native antigens and their precipitation with specific antibodies: they are not very appropriate for the investigation of processed denatured mixtures. This report describes an immunoassay based on the more recent but well-established enzyme-linked immunosorbent assay (ELISA) procedure, which in this case is specific for soya proteins that have been solubilised in urea and then 'renatured' by removing or diluting the denaturant. Levels of soya protein 100 g-I total protein (nominally 100%) were determined with 34 commercial soya products, using a standard reference antigen. Normal expected levels were observed with flours (average 107 %) and isolates (108 %), while results with concentrates (82 " , ) and texturates (79 %) were somewhat lower. Some specialised products gave little or no response, presumably because they are hydrolysed. Meat, milk, egg, wheat and field bean proteins displayed negligible interference. These preliminary results suggest that the ELISA procedure will provide a convenient general method for the qualitative characterisation and quantitative estimation of individual proteins in food products even after severe processing; it seems more attractive than many other methods reported. Imrnunoassay is capable of large numbers of inexpensive but sophisticated determinations of specific food components. The food analyst should regard ELISA (for the determination in situ of specific antigens in mixtures) as a powerful technique complementary to classical chromatographic and electrophoretic methods which depend on separation before determination.

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Irradiated water and the headspace above it has been analysed using a novel hydrogen-specific electronic sensor, calibrated with standard hydrogen dilutions. The results demonstrate that this detector is well capable of distinguishing between irradiated and non-irradiated water through the quantitative determination of the hydrogen generated during irradiation. This hydrogen diffuses away within 12 h if the water is left in an open vessel. The potential application of the detector for monitoring irradiated food is therefore limited to packaged or solid foods which retain the characteristic hydrogen marker.

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