Gas Chromatography-Mass Spectrometry (GC-MS) Profiling of Hops and Some Nigerian Potential Hop Substitutes: Comparative Studies in Beer Brewing

Abstract

Isomerized hop extract and methanolic extracts of Azadirachta indica, Garcinia kola, Gongronema latifolium and Vernonia amygdalina were profiled by the application of Gas Chromatography-Mass Spectrometry (GC-MS). The isomerized hop extract and ethanolic extracts of the plant species were used to brew beers. The aim was to study the GC-MS profiles of all the extracts comparatively and to investigate some physicochemical properties of beers brewed with hop extracts and in comparison, with beers brewed with extracts from the four Nigerian plants. The profiling of the metabolites in hop extracts and those of the Nigerian plants was carried out using Gas Chromatography - Mass Spectrometer. The physicochemical properties of the finished beer products were also carried out using standard methods. Beers brewed with extracts from the Nigerian plants were statistically ranked by the application of Analysis of Variance (ANOVA) to ascertain their potentiality. The GCMS results showed that these plants contained metabolites comparable to those of hops, although some metabolites [dehydro-cohumulunic acid; 4,4-dimethyl- 2-buten-4-olide; 1,2-dimethyl-cyclopropane carboxylic acid; lupulone; 2,5-dimethyl-2-hexanol; 4,4,5,5-tetramethylbicyclo hexyl-6-ene-2,3-dione; octadecanoic acid, oxiranyl methyl ester and 1,2-benzenedicarboxylic, bis(-2-ethyl hexyl) ester] present in hops were absent in the Nigerian plants. Isomerized hop, hop leaf, G. kola and V. amygdalina extracts contained 14, 11, 12 and 9 metabolites respectively while those of A. indca and G. latifolium contained 10 metabolites each. The physicochemical properties of the brewed beers revealed that the alcohol content in all the beer samples ranged from 3.43-3.75%, total acidity (0.132-0.324%), pH (5.47-5.68), turbidity (5-125NTU), total solids (3.66- 8.16%) and bitterness level (25.38-39.62IBU). The concentration of arsenic in the beer samples ranged from 1.44- 1.77ppm, cadmium (0.00-0.97ppm) and copper (0.10-2.70ppm). Test of significant (p-value) in all the tested plants was greater than 0.05 at 95% confidence interval. Consequently, the extracts from tested Nigerian plants could be used as suitable substitutes for hops in beer brewing without alteration of physicochemical properties of beer, G. kola having the greatest potential as substitute for hops.