Characterization and quantification of free and esterified 9- and 13-hydroxyoctadecadienoic acids (HODE) in barley, germinating barley, and finished malt.
The analysis of (R)-9- and (S)-9-hydroxy-10E,12Z-octadecadienoic acid as well as (R)-13- and (S)-13-hydroxy-9Z,11E-octadecadienoic acid (HODE) as free acids, esterified in triacylglycerols (storage lipids), and esterified in polar lipids (phospholipids, glycolipids, etc.) in barley, germinating barley, and finished malt was performed using [13-(18)O(1)]-(S)-13-HODE isotope dilution assays with GC-MS and straight- and chiral-phase HPLC. 9- and 13- HODE occur approximately racemically in barley, indicating an autoxidation. The enantiomeric excesses increase to 78% S for free 9-HODE and to 58% S for free 13-HODE in germinating barley as a result of lipoxygenase-2 (LOX-2) catalysis, but free HODEs are at low concentration. More than 90% of HODEs in barley and malt are esterified. In the storage lipids of green malt 53 mg/kg 9-HODE and 147 mg/kg 13-HODE were detected. This ratio of 30:70 reflects the regioselectivity of the LOX-2 enzyme in malt. In the polar lipids 45 mg/kg 9-HODE and 44 mg/kg 13-HODE were characterized. The latter indicate a hitherto unknown 9-lipoxygenase activity with polar lipids as substrates. During kilning the contents of most HODEs decreased significantly due to chemical and enzymatic degradation, whereas polar-esterified (R)-13-HODE increased (43%) in the finished malt.
Hübke
Holger
H
Institut für Biotechnologie, Molekularanalytik, Technische Universität Berlin, Seestrasse 13, D-13353 Berlin, Germany.
Garbe
Leif-Alexander
LA
Tressl
Roland
R
D002851:Chromatography, High Pressure Liquid; D002523:Edible Grain / Q000737:chemistry*; D004951:Esterification; D008401:Gas Chromatography-Mass Spectrometry; D018525:Germination; D001467:Hordeum / Q000737:chemistry*; D008041:Linoleic Acids / Q000032:analysis* / Q000737:chemistry; D044243:Linoleic Acids, Conjugated / Q000032:analysis* / Q000737:chemistry; D012639:Seeds / Q000737:chemistry*; D013237:Stereoisomerism
D008041:Linoleic Acids; D044243:Linoleic Acids, Conjugated; C024347:9-hydroxy-10,12-octadecadienoic acid; C024348:13-hydroxy-9,11-octadecadienoic acid