High-throughput micro plate assays for screening flavonoid content and DPPH-scavenging activity in sorghum bran and flour.

BACKGROUND Sorghum possesses phenolic compounds that are health-promoting constituents of the grain. There are approximately 40 000 sorghum accessions, many of which have not been evaluated for the grain's health-promoting potential. Conventional methods for measuring total phenolic content, flavonoid content and 2,2-diphenyl-1-picrylhydrazyl (DPPH)-scavenging capacity are time-consuming and labour-intensive, resulting in low overall throughput. The objective of this study was to develop a high-throughput screening assay for large sorghum sample sets to determine flavonoid and phenolic content and to modify existing DPPH and total phenolic assays. RESULTS The 96-well assays exhibited a correlation of > 0.9 with the conventional assays. The 96-well assays allowed for up to 64 samples to be run per day compared with 20-24 samples (depending on the test) for the conventional methods. The 96-well assays had excellent accuracy (97.65-106.16% recovery), precision (1.06-8.28% coefficient of variation (CV)) and reproducibility (1.32-2.13% CV inter-day and 1.36-2.09% CV intra-day). CONCLUSION The high-throughput 96-well plate method proved to be as robust and reproducible as the conventional method for determining total phenolic content, flavonoid content and DPPH-scavenging capacity in either sorghum bran or flour.