Short Note #22: Protein Determination in Chocolate According to Kjeldahl Method

Milk and Dark ChocolateThis short note describes a simple and fast procedue for protein determination in chocolate according to the Kjeldahl method, as detailed in in the AOAC 970.22 regulations. Visit our Kjeldahl Applications section to download this short note and review all our other available application studies.

Introduction:
Protein determination is one of the key analyses performed in the food industry. The samples 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 (6.25 for chocolate) to obtain the protein content.

Instrumentation:
Buchi SpeedDigester K-436, K-439, Buchi Kjeldahl Sampler System K-370/K-371

Samples:
Milk chocolate and Dark chocolate, labelled protein contents 9% and 5%, respectively.

Conclusion:
The determination of protein contents in chocolate 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 [See Note for table Data References] with low relative standard deviations. The total digestion time is approximately 120 min.

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