Research On Polyphenol Antioxidant Activity Of The Proso Millet Pericarp

In this study, fifteen proso millet varieties with different colors of seed coat were employed to study phenolic compounds in their seed pericarp. Firstly, in the present study, base on emulsification-assistant extraction, single factors and response surface methodology trails were applied to optimizer conditions of polyphenol extract from proso millet pericarp. Secondly, based on the optimized conditions, I compare the antioxidant activities and phenolic compounds content of fifteen strains of proso millet pericarp, using radical DPPH scavenging activity method,β-carotene-linoleic acid method and radical ABTS scavenging activity method. Finaly, through high performance liquid chromatography, the phenolic acid and the flaconols compound extracted from proso millet pericarp were analyzed. The results are as follows:(1) The optimized conditions were as follows: acetone concentration 90%, sample-to-solvent ratio 1:30(g/mL)and extract times 5. In the optimized conditions, phenolic yield was 1.46%.(2) The darker the proso millet pericarp was, the higher the L* value was; The reder the proso millet pericarp was, the higher the a* value was. Total phenolic compounds contents in 100g whole pericarp flour ranged from 935.73 to 1909.29 mg gallic acid(3 to 6 times wheat bran), while most of the phenolic compounds in pericarp were in the bound form. Total flavonoid contents in 100g whole pericarp flour ranged from 24.79 to 68.24 mg rutin, while most of the flavonoid compounds in pericarp were in the free form. The darker the proso millet pericarp was, the higher the free phenolic contents and the free flavonoid contents were. The order of radical scavenging against DPPH?, radical scavenging against ABTS? and AAC value of proso millet varieties with different colors of seed coat is: brown varieties> red varieties> gray variety> white varieties; L* value, b* value, DPPH assay, ABTS assay had significant correlations with phenolic compounds content, which showed that phenolic compounds caused different colors of seed pericarp.(3)The nine phenolic compounds: gallic acid, catechin, p-coumaric acid, chlorogenic acid, ferulic acid, protocatechuic acid, rutin, quercetin and vanillic acid were identified in the free phenolic compound extractive. Gallic acid existed in the free form only. The catechin content was the highest in the free part(0.49~1.41mg/g). The ten phenolic compounds: catechin, p-coumaric acid, chlorogenic acid, ferulic acid, protocatechuic acid, rutin, quercetin, caffeic acid, syringic acid and vanillic acid were identified in the bound phenolic compound extractive. Caffeic acid existed in the bound form only. The main compounds in the bound part were catechin(0.38~1.50mg/g) and p-coumaric acid(0.02~1.20mg/g).