HPAEC analysis of amino acids in sugar beet samples: Method development and application

Among the various nitrogenous compounds in sugar beet, the amino acids are the most important as far as the technological quality of the beets is concerned. This so-called "harmful nitrogen" takes part in Maillard reaction in the presence of reducing saccharides (e.g. invert sugar), and this is responsible for the undesirable formation of colorants in sugar manufacture. Additionally, from the amide part of the amino acids, ammonia is liberated during juice purification and evaporated. The ammonia finds its way back into the condensate, which must be purified by (expensive) biological treatment before it can be discharged. Usually, the alpha-amino-nitrogen (alpha-NH2-N) content of sugar beets is analyzed, however this total figure does not give any information on the composition of the amino acids, e.g. the amide content. The occasionally observed large difference in the amide/alpha-NH2-N ratio. as well as the absolute level of alpha-NH2-N in sugar beets has caught the attention and has encouraged us to investigate the origin of this phenomenon. For that pur-pose a high-performance anion exchange chromatography (HPAEC) method has been developed in order to separate the amino acids, using integrated amperometry as the electrochemical detection. Sample preparation (solid phase extraction) is necessary to remove the surplus of sucrose, which otherwise exhibits too much interference in the analysis. An outline will be presented of the method development, including a comparison between the use of different columns for the chromatographic separation. The method has been applied for the screening of the amino acid composition in beet brei samples of different origin. A brief report of this preliminary study will be given.