Faculty: Physical Sciences
Department: Pure And Industrial Chemistry
Okafor, V. N
The potential of four selected Nigerian plants namely Azadirachta indica (neem), Garcinia kola (bitter cola), Gongronema latifolium (heckel) and Vernonia amygdalina (bitter leaf) as substitutes for hops in beer brewing were evaluated in terms of methanolic and ethanolic extracts. The relative proportion of each constituent in hop extracts and those of the Nigerian plants were investigated using Gas Chromatography - Mass Spectrometer (GC-MS), phytochemical screening using standard methods and metal analysis using Atomic Absorption Spectrophotometer (AAS) of all the samples were carried out. The physicochemical properties of the finished beer products were also studied using standard methods. These Nigerian plants were statistically ranked by the application of Analysis of Variance (ANOVA). The GCMS results showed that these plants contained constituents comparable to those of hops, although some constituents [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-tetramethyl-bicyclo 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 contained a total number of 14, 11, 12 and 9 constituents respectively while A. indca and G. latifolium each contained a total number of 10 constituents. Phytochemical assay revealed that alkaloid content in all the extracts ranged between 3.2-4.8%; tannin ranged from 2.0-4.8%; saponin ranged between 0.80-5.20%; phytate ranged from 0.99-1.68%; trypsin inhibitors ranged from 2.80-17.30%; haemagglutini ranged from 3.879-7.240% and cardiac glycoside ranged from 3.5-6.0%. The concentration of oxalate ranged from 0.0405- 0.1020mg/100g, cyanogenic glycoside ranged from 0.216-0.810ppm and hydrogen cyanide ranged from 0.540-1.404ppm. The AAS results showed that the concentration of metals investigated in all the samples were calcium (16.300–33.145ppm), sodium (92.019–101ppm), potassium (8.297–206.838ppm), magnesium (19.331-22.188ppm), lead (Not detected), manganese (0.426-38.628ppm), cobalt (0.00–0.002ppm), zinc (0.963-17.944ppm), mercury (0.00–1.127ppm) and iron (0.159-8.614ppm). The physicochemical properties of the brewed beers revealed that the alcohol content in all the beer samples ranged between 3.43-3.75%, total acidity from 0.132-0.324%, pH (5.47-5.68), turbidity (5-125NTU), total solids ranged from 3.66-8.16% and bitterness level ranged from 25.38-39.62IBU. The concentration of arsenic in the beer samples ranged from 1.44-1.77ppm while that of metals were cadmium (0.00-0.97ppm) and copper (0.10-2.70ppm). It was established from ranking that the order of closeness of the vegetables investigated to isomerized hop extract was G. latifolium (0.971) > G. kola (0.860) > A. indica (0.751) > V. amygdalina (0.551) while that to hop leaf extract was V. amygdalina (0.958) > G. kola (0.686) > G. latifolium (0.578) > A. indica (0.347). Hence, the extracts from tested Nigerian plants could be used as suitable substitutes for hops in beer brewing without alteration of physicochemical properties of beer. Extract of G. latifolium had the greatest potential as substitute for isomerized hop extract and that of V. amygdalina was the closest substitute for hop leaf extract. Consequently, academic activity in the area of mixtures/blends of extract of plant species which mimic hop taste is strongly recommended.