Amino Acid Quantification in the Presence of Sugars using HPLC and Pre-Column Derivatization with 3-MPA/OPA and FMOC-Cl
Irena Kralj Cigić,1* Tatjana Vrščaj Vodošek,2 Tatjana Košmerl3 and Matija Strlič1
1 University of Ljubljana, Faculty of Chemistry and Chemical
Technology, Aškerčeva 5, SI-1000 Ljubljana, Slovenia
2 Vinakoper d.o.o. Wine Cellar, [marska cesta 1, SI-5000 Koper,
Slovenia
3 University of Ljubljana, Biotechnical Faculty, Department of Food
Science and Technology, Jamnikarjeva 101, SI-1000 Ljubljana, Slovenia
* Corresponding author: E-mail:
irena.kralj-cigic@fkkt.uni-lj.si
Abstract
Determination of free amino acids (AA) in musts and young wines using pre-column
derivatization with 3-MPA/OPA for primary AA and FMOC-Cl for secondary AA was
studied. As samples differ in their sugar content considerably, the influence of
sugars on derivatization was investigated using two internal standards: (i)
primary AA norvaline and (ii) secondary AA sarcosine, in real samples and in
model fructose and glucose solutions. A strong matrix effect was observed,
especially when concentrations of sugars exceeded 50 g/L. The influence of
sugars on derivatization of secondary AA sarcosine was more pronounced than on
the primary AA norvaline. For quantitative evaluation of AA in samples with
variable but high sugar content we propose to use external calibration in
combination with internal standard method, where the response factors for
individual AA are corrected with respect to that of internal standards.
Keywords: Amino acids, sugars, 3-MPA/OPA, FMOC-Cl, wine, must