Comparison of analytical methods for measuring protein content of whey protein products and investigation of influences on nitrogen conversion factors

Whey protein products are important ingredients that are used to improve and augment the nutritional and functional properties of a wide variety of foods including infant formula. Their protein contents are an intrinsic aspect of their value and how these are determined can be influenced by the type of method selected. The Kjeldahl method relies upon determination of the nitrogen content and then multiplication using a nitrogen conversion factor. An alternative technique is to measure the constituent amino acids and sum them. We show, for a representative selection of whey protein products, that the Kjeldahl and amino acid methods afford different results, and we explain these differences.