Quantification of Wheat TAXI and XIP Type Xylanase Inhibitors: A Comparison of Analytical Techniques

To date, three different techniques are available for the quantification of TAXI and XIP type proteinaceous xylanase inhibitors in cereals. A first approach is based on the determination of the residual activities of xylanases (also referred to as endo-1,4-β-d-xylanases, EC 3.2.1.8), which are specifically inhibited by these inhibitors, after incubation with sample containing the inhibitors. The other two techniques are immunoblotting and ELISA which are based on recognition of TAXI and XIP proteins by specific antibodies. TAXI, as well as XIP, are easily extracted by aqueous buffers. Hence, the large difference in their concentrations (2-10 fold higher for XIP than for TAXI in whole meal) is not caused by differences in extractability. The repeatabilities of the three techniques are comparable. The intra-assay and inter-assay coefficients of variation were 6-7 and 10-14%, respectively, which is in the range of values described for methods to quantify other compounds in plant and animal tissues. The three methods give comparable results, suggesting they have similar accuracies. The choice of the technique to be used will depend not only on the sensitivity and dynamic range needed, but also on its technical simplicity and the need for high-throughput analysis.