Protein on the Nutrition Label
The protein analysis for measuring nitrogen content on food labels is performed by either the Kjeldahl or Dumes method. According to Dr. Sam K.C. Chang, Department of Cereal and Food Science, North Dakota State University, the Dumas method is used more frequently in nutrition labeling since it is faster. Both methods include measurement of melamine, a toxic protein adulterant, in the total nitrogen content when declaring protein analysis results . The 2008 Chinese melamine scandal brings this concept into focus. It is called “protein spiking” so that the protein content is inflated. There is no easy way to detect the nitrogen bound proteins from other sources added to protein powders and supplements as adulterants. Free amino acid products are the only way to know the protein levels that are bioavailable .
The Nutrition Labeling and Education Act (NLEA) requires percent daily value, which is determined using the Protein Digestibility- Corrected Amino Acid Score (PDCAAS), to be used on the label. Dr. Denise Smith states in Food Analysis that time and cost associated with the PDCAAS method, result in the label only expressing the protein amount and not the protein efficiency ratio (PER) . Consequently, using the nutrition label on protein enriched products to assess protein quality and quantity is inaccurate and inadequate for bariatric nutrition needs.
Sarwar and McDonough refute the PER as a better means of protein quality evaluation . They recommend an amino acid score corrected for true digestibility as the most suitable method for predicting protein quality in foods for humans. A detailed method was provided in their analytical chemistry article but no current use of this method has been identified.