Chemical profile, antioxidant activities and allelopathic potential of liquid waste from germinated brown rice

We examined the liquid waste of germinated brown rice (Oryza sativa L.) (GBR) for total phenols, flavonoids and antioxidant and allelopathic activities. The butanol extract showed the strongest antioxidant activity, while the ethyl acetate extract exhibited maximal inhibition on germination and growth of radish (Raphanus sativus L.). Total flavonoid content was reversely proportional to allelopathic level (r(2)=0.63), whilst antioxidant activities showed negligible coefficient correlations. Analysis of GC-MS (gas chromatography mass spectrometry) revealed the presence of many putative constituents, of which 1-propene-1,2,3-tricarboxylic acid, tributyl ester was the principal compound in butanol, acetate and hexane extracts. There were 18, 6, 12 and 3 compounds putatively identified in butanol, ethyl acetate, hexane and aqueous extracts, respectively. In the butanol extract, 2,3-dihydro-benzofuran, phenyl ester carbamic acid, 2-methoxy-phenol, 3,4-diol-1,5-heptadiene, 1-(2-hydroxy-5-methylphenyl)-ethanone and methyl ester-3-(4-hydroxyphenyl)-2-propenoic acid were the predominant substances. In the ethyl acetate extract, methyl ester-hexadecanoic acid and methyl ester-9-octadecenoic acid and bis (2-ethylhexyl) ester-hexanedioic acid were the dominant compounds. In the hexane extract, methyl ester-hexadecanoic, n-hexadecanoic acid, methyl ester-9-octadecenoic acid, 10-hydroxy-methyl ester-hexadecanoic acid and E-2-((hex-3-enyloxy) carbonyl) benzoic acid podocarpan-12 beta-ol were the major constituents. There were three key substances observed in the aqueous extract, including acoradien, beta-cis-caryophyllene and monoethanoamine. The compounds identified in the liquid waste of GBR production might be potential for weed management.