NDMA (n-nitrosodimethylamine) in Malt/Beer
During the malting process, barley is forced to germinate, after which the grain is dried in kilns. This process freezes the sugar and flavour compounds for the brewing process. During the kiln drying process, nitrosamines may be formed in the grain, which could remain within the extract and still be present in the final brewed product. Many recently used techniques, minimise the formation of nitrosamines., However, low levels of these carcinogenic compounds still remain. Therefore, all malt used in the brewing process needs to be analysed for its nitrosamine content. It is important to monitor the final product as well as the malt, to help regulate the exposure of nitrosamines from the consumed liquid.
The Ellutia 200 Series Gas Chromatograph with an EL-WAX column was utilised alongside the 800 series Thermal Energy Analyser (TEA)
Samples were extracted in duplicate. Each replicate had 50 grams of malt ground up and had 100 ml deionised water added. The extract was filtered through a Whatman Grade 1 filter paper and 1 ml of 10 ppm NDPA (n-nitroso di propylamine) internal standard was added to one extract (this generates a 100 ppb NDPA spiked sample). The samples were then made up to 100 ml with deionized water volumetrically. To a vial, 10 ml of extract, 3 grams of sodium chloride and 10 ml of dichloromethane (DCM) was added and shaken for 5 minutes. Then the layers were left to separate for 15 minutes. The lower layer containing DCM was pipetted out into a clean vessel. 10 ml of DCM was added to the extract and the liquid/liquid extraction step was repeated. After this step, the DCM (final volume approx. 20 ml) was dried using 1 gram of sodium sulphate and then preconcentrated to 1 ml under a nitrogen flow of approx.1 l min-1. A 1 µl injection of the concentrated DCM was directly analysed.
The identity of the internal standard was confirmed against the 8 component nitrosamine mix standard. This shows that the NDPA internal standard used has the same retention time as the NDPA contained within the standard (figure 1).The peak areas for the spiked sample compared with the standard for NDPA showed good correlation, indicating a good recovery of the internal standard, and thusly, indicating very limited losses of any potential nitrosamines from within the sample during the pre-paration steps. The unspiked sample showed no peaks within the retention times of any of the nitrosamines in this standard mix. As such, this malt sample showed no observable response for NDMA or any other nitrosamines.
25 ml of lager was sonicated for 10 minutes to remove any dissolved gases. 10 ml was transferred to a centrifugal tube, 3 grams of sodium chloride was added, followed by 1 mL of DCM and the solution was shaken for 5 minutes. The sample was then left to separate out for 15 minutes. The DCM layer was pipetted into a new vial and 1 gram of sodium sulphate was added to capture any remaining aqueous solution. A 1 µl injection of the DCM solution was directly analysed.
NDMA detection limits for this instrument have recently been generated and show that <1 ppb NDMA can be seen. For the malt sample the results would be declared as none detected <1 ppb, the beer would also be declared as <1 ppb NDMA, however, there was a response found for NDBA (n-nitrosobutylamine) of 67 ppb.