Normalisation of data from allergens proficiency tests.

The problem of allergen analysis using ELISA kits from different commercial products giving significantly different results is widely acknowledged. The effect on proficiency testing results is that different assigned values have to be generated for the different kits used. Some experimental Food Analysis Performance Assessment Scheme (FAPAS) proficiency tests aimed to establish whether the use of a standardised calibrant could be used to normalise the complete data set without recourse to differentiation. Three recent FAPAS proficiency tests (2776 peanut, 2778 soya and 2781 gluten) sent out a second spiked sample, in addition to the usual spiked and unspiked samples. Further analysis of the data was undertaken after the completion of the tests. The ratio of the submitted results for the two spiked samples yielded complete data sets which could be tested for normality of the distribution. Where the raw data for each individual test sample was clearly non-normal and multi-modal, the ratio data yielded a much more normal and symmetrical distribution. The use of one of the test samples as a single-point calibrant has some limitations but the principle of applying a standardisation clearly works. The development of internationally recognised sets of certified reference calibration standards for use by allergens testing laboratories would greatly benefit the analysis.

Detection of sugar syrups in apple juice by delta(2)H per thousand and delta(13)C per thousand analysis of hexamethylenetetramine prepared from fructose.

An improved procedure for determining (13)C and (2)H isotope ratios, using gas chromatography-isotope ratio mass spectrometry (GC-IRMS), has been developed for identifying the addition of low cost commercial sugar syrups to apple juices and related products. Isotopic techniques are commonly used to identify the addition of low cost sugars to fruit juices and are difficult to circumvent as it is not economically viable to change the isotopic ratios of the sugars. The procedure utilizes the derivative hexamethylenetetramine, which is produced through chemical transformation of a sugar degradation product and provides position-specific (13)C and (2)H ratios that relate to the parent sugar molecule. The new procedure has advantages over methods using nitro-sugar derivatives in terms of analysis time and sensitivity. The differences between the delta(2)H per thousand and delta(13)C per thousand values of the 100 authentic apple juices and beet and cane commercial sugar syrups permit their addition to be reliably detected.