Air classification as a useful technology to obtain phenolics-enriched buckwheat flour fractions

Air classification is a valuable process to obtain flours enriched in phenolic compounds. In this study, dehulled buckwheat grain flour was micronized and air classified obtaining two couple of fractions with different yields (fine fraction 70% and coarse fraction 30%, and fine fraction of 80% and coarse fraction 20%). The total content of phenolic compounds (by HPLC-MS) in coarse fractions increased 1.7-2.1 times compared to fine fractions. In addition, coarse fractions have shown a total phenolic content of 1.4-1.7 times more than dehulled buckwheat flour. Moreover, the antioxidant activity was evaluated using two different assays: FRAP (The ferric reducing antioxidant power) and DPPH (2,2-diphenyl-1-picrylhydrazyl radical). Coarse fractions have shown FRAP values 1.2-1.3 times higher than fine fractions, whereas the DPPH showed a slight increase in coarse fractions in comparison with buckwheat flour and fine fractions. In addition, FRAP and DPPH have exhibited a significative positive correlation with the flavonoids, phenolic acid derivatives and total phenolic content. These results have shown that air classification is an effective technique in order to obtain coarse flour fractions enriched in phenolic compounds such as swertimacroside, (epi)-afzelchin-(epi)-catechin-O-dimethyl gallate, rutin and caffeic acid hexose, among others.