Non-destructive determination of nitrogen in malting barleys by instrumental photon activation analysis and its comparison with the Dumas method

Abstract

Instrumental photon activation analysis (IPAA) was used to measure the nitrogen content of malting barleys used in brewing and breeding in the Czech Republic. The study compares the fast and non‐destructive IPAA method with the classical Dumas method requiring combustion of the sample. The IPAA procedure for nitrogen assay is based on measuring the positron–electron annihilation γ line at 511 keV from the photoactivation product 13N, which is interfered with by other positron emitting nuclides. Interference from 15O can be eliminated by counting after a sufficient decay time. Interferences from 34mCl and 38K can be corrected via measuring their specific γ lines at 146.4 and 2167.7 keV, respectively. The IPAA procedure has been verified by analysis of several biological reference materials and is suitable for nitrogen measurement in cereals and other plant materials with a detection limit down to 10−2 wt%. Nitrogen contents in malting barleys ranged from 1.4 to 2.2 wt% and were dependent on the cereal variety and growth conditions (fertilizer use and chemical protection). Copyright © 2018 The Institute of Brewing & Distilling

Comparison between barley malt protein quantification methods

“…In combustion, nitrogen is converted into NO x , then reduced and measured as N 2 , which overestimates the protein content (Garcia et al, 2015); the same applies to CHN. On the other hand, Kjeldahl does not measure inorganic nitrogen, so its results tend to be lower than combustion ones (Krausová et al, 2018). Therefore, the lower results obtained by digestion methods was caused by the fewer inorganic compounds measured; although they can be quantified if the reduction step is not adequate during digestion, which might be the case for FIA (Jung et al, 2003).…”

“…The Dumas method or nitrogen combustion method was created in 1831 and avoids the use of corrosive chemical products; but it does not only quantify protein, it also considers inorganic nitrogen including nitrate, nitrite, and some other organic ones, as nucleic acids. This causes the protein content to be overestimated (Jung et al, 2003;Garcia et al, 2015;Krausová et al,2018). The Kjeldahl method was created in 1833 and meant for the brewing industry, as it can be used to measure the differences in protein content in grains throughout the malting and fermentation processes (Kjeldahl, 1883;Sáez-Plaza et al, 2013a).…”