A simple and fast procedure for protein determination in bran according to the Kjeldahl method, as described in the LFGB §64 L15.00-3 regulations, is introduced below. The sample is digested with sulfuric acid using the SpeedDigester K-436 or K-439, followed by distillation and titration with the Kjeldahl Sampler System K-370/K-371.
The samples, as noted above, require digestion with sulfuric acid to convert nitrogen into ammonium sulfate. After conversion to ammonia through the alkalinization with sodium hydroxide, the sample is distilled into a boric acid receiver by steam distillation, followed by a titration with sulfuric acid solution. The nitrogen content is multiplied by a sample-specific factor (5.7 for wheat and oat) to obtain the protein content.
The determination of protein contents in bran according to Kjeldahl using SpeedDigester K-436, K-439, and Kjeldahl Sampler System K-370/K-371 provides reliable and reproducible results that correspond to the labelled values and literature, included in the study, with low relative standard deviations. The total digestion time is approx. 85 min (K-439) or 100 min (K-436).