Wort Free Amino Nitrogen Analysis Adapted to a Microplate Format

The standard method for determining wort free amino nitrogen content is a long-established but now relatively outdated procedure, calling for the use of test tubes, marbles, several water baths (boiling and 20°C), manual sample transfers, and a conventional spectrophotometer. Currently, many malting quality laboratories avoid use of this cumbersome manual system by adopting automated chemistry analysis systems as their in-house standard method for wort free amino nitrogen analysis. Several recent papers have taken a somewhat different approach to measuring malting quality by adapting the basic analytical method to microtiter plates, microplate readers, and related instrumentation. This streamlines sample handling and increases sample capacity. However, results from the several free amino nitrogen methods published previously have not been directly compared. In this study, we analyzed several malts using the standard ASBC Wort-12 method, our standard Skalar segmented flow analysis chemistry system, and several variations of those two chemistries in microplate formats to compare the results obtained by the different analysis systems. Among these methods, the results from the manual ASBC Wort-12, the automated Skalar system, and a microplate-format assay based on the Skalar reagents agreed well. Surprisingly, however, direct adaptation of the Wort-12 reagents, times, and temperatures to the microplate format yielded inconsistent results. We examined a number of parameters in the microplate-format Wort-12 implementation but were unable to identify a single factor responsible for the divergence of results. From these results, we recommend adapting the chemistry from the Skalar segmented flow analysis system to a microplate format for analysis of wort free amino nitrogen content.