EFFECT OF MALTING ON FLAVONOID COMPOUNDS AND ANTIOXIDANT ACTIVITY IN FOUR AUSTRALIAN SORGHUMS
A. KHODDAMI (1), M. A. Wilkes (1), T. H. Roberts (1). (1) Department of Plant and Food Science, Faculty of Agriculture and Environment, University of Sydney, Sydney, Australia
Research on the complement of secondary metabolites in sorghum grain is well advanced but less is known about the effects of malting on these compounds. Grains of four Australian sorghum cultivars were studied to determine the effects of malting on (i) flavonoid compounds and (ii) antioxidant activity by applying the 2,2'-Azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) and 1,1-Diphenyl-2-picrylhydrazyl (DPPH) methods. The sorghum grain (harvested in 2011) was analysed for concentrations of total phenolics, flavonoids, condensed tannin, flavan-4-ol, as well as for antioxidant activity. Eriodictyol, naringenin, apigenin and luteolin were identified in all unmalted and malted samples, with naringenin being dominant. Among the grain samples, malting reduced the content of total phenolics and concentrations of flavonoids, with the exception of apigenin. None of the grain samples had a pigmented testa, indicating a lack of condensed tannin. For the unmalted and malted sorghums, respectively, the following mean concentrations for each assay (averages of four cultivars) were obtained: 3.09 and 2.57 mg GAE/g for total phenolics; 21.02 and 19.60 umol TE/g for radical scavenging activity (ABTS), 9.73 and 6.64 umol TE/g for radical scavenging activity (DPPH); 9.1 and 9.66 ug/g for flavones (apigenin and luteolin); and 97.64 and 62.45 ug/g for flavonones (eriodictyol and naringenin). For each assay, unmalted and malted samples for specific varieties were significantly different in some cases but not others. In conclusion, malting appears to affects the concentrations of secondary products in sorghum, knowledge of which is important in assessing the quality of sorghum malt for food.
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