The traditional Kjeldahl method and the combustion (Dumas) method have been widely used for measuring total protein content in foods and dietary supplements. However, these methods are not specific for protein since they rely on total nitrogen determination as a marker to estimate the amount of protein. The liquid chromatography with tandem mass spectrometry (LC-MS-MS), a powerful analytical technique that combines the separating power of liquid chromatography with the highly sensitive and selective mass analysis capability of triple quadrupole mass spectrometry, provides specific information of protein based on its unique peptides. In this presentation, the enzymatic digestion and LC/MS/MS technologies have been successfully adopted to identify different protein species including milk, pea, rice and soy. The specific protein of each protein species was selected based on SDS-PAGE technology, then the protein was enzymatically digested by trypsin into peptides. Three specific peptides were selected for each protein species based on its protein sequence, and these selected peptides were analyzed on LC/MS/MS. The blank, laboratory control sample (LCS) and minimal report limit sample (MRL sample at 2000 ppm) were used to determine the presence or non-presence of these protein species. This protein identification method has been successfully validated and applied to hundreds of samples over last 3 years.

Identification of milk, pea, rice and soy protein by liquid chromatography with tandem mass spectrometry (LC/MS/MS)

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

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