Chirality of amino acids of microorganisms used in food biotechnology

Abstract

Bacteria of the genera Acetobacter, Bifidobacterium, Brevibacterium, Lactobacillus, Micrococcus, Propionibacterium, and Streptococcus, which are used as so-called starter cultures for the large-scale production of fermented foods and beverages in food biotechnology, have been investigated for the chirality of their amino acids (AA) by gas chromatography (GC). Bacteria were grown in complex media, centrifuged, and washed with 0.85% aqueous NaCl. Aliquots were totally hydrolyzed (6 M HCl, 110 degrees C, 18 h), or extracted with 70% aqueous ethanol in order to isolated free AA. The AA were adsorbed on Dowex WX 8 cation-exchanger, eluted with 4 M ammonia and converted into their N(O)-trifluoro-acetyl(TFA) 2-propyl esters or TFA methyl esters. The AA derivatives were investigated by capillary GC using the chiral stationary phases Chirasil-L-Val, Chirasil-D-Val, and Lipodex E. Besides L-AA, in all bacteria D-amino acids (D-AA) were detected; those in the highest relative amounts were D-Ala and D-Asp (occurring in all bacteria) and, in several cases, D-Glu. Lower, but significant amounts of other D-AA such as D-Ser, D-Pro, D-Val, D-Thr. D-Ile, D-Leu, D-Met, D-Phe, D-Tyr, D-Orn, and D-Lys were also detected in certain bacteria. These findings explain the origin of D-AA found in all fermented foods and drinks produced with the aid of bacterial starter cultures.