Enzymatic hydrogenation of trans-2-nonenal in barley.
Conversion of undesirable, taste-active compounds is crucial for using barley as a suitable raw material for beer production. Here, ALH1, a barley alkenal hydrogenase enzyme that reduced the alpha,beta-unsaturated double bond of aldehydes and ketones, was found to convert trans-2-nonenal (T2N), a major contributor to the cardboard-like flavor of aged beer. Although the physiological function of ALH1 in barley development remains elusive, it exhibited high specificity with NADPH as a cofactor in the conversion of several oxylipins-including T2N, trans-2-hexenal, traumatin, and 1-octen-3-one. ALH1 action represents a previously unknown mechanism for T2N conversion in barley. Additional experimental results resolved the genomic sequence for barley ALH1, as well as the identification of a paralog gene encoding ALH2. Interestingly, T2N was not converted by purified, recombinant ALH2. The possibility to enhance ALH1 activity in planta is discussed--not only with respect to the physiological consequences thereof--but also in relation to improved beer quality.
Hambraeus
Gustav
G
Carlsberg Research Center, Gamle Carlsberg Vej 10, DK-2500 Copenhagen, Denmark. gustav.hambraeus@crc.dk
Nyberg
Nils
N
D000447:Aldehydes / Q000378:metabolism*; D000595:Amino Acid Sequence; D001515:Beer / Q000032:analysis; D015870:Gene Expression; D001467:Hordeum / Q000201:enzymology*; D006865:Hydrogenation; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D010088:Oxidoreductases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins; D013379:Substrate Specificity
D000447:Aldehydes; D011994:Recombinant Proteins; C013166:2-nonenal; D010088:Oxidoreductases