Properties of Polyphenols and Xylooligosaccharides Obtained Biotechnologically from Processed Millets

Abstract

Introduction. Thousands of tons of millet grain are processed annually in the world. Husk is the main waste of millet processing and can produce biologically valuable components. The present research offers a new biotechnology for the production of biologically active substances (BAS), namely polyphenols and xylooligosaccharides (XOS), from millet husk.
 Study objects and methods. Millet husk was tested for the mass fraction of protein, moisture, starch, fiber, and reducing substances, as well as for antiradical activity, qualitative and quantitative composition of phenolic substances, fractional composition of carbohydrates, monosaccharide composition of polysaccharides, qualitative and quantitative compositions of XOS concentrates.
 Results and discussion. The obtained BAS concentrates contained 0.90% of protein and 91.50% of carbohydrates, including 68.50% of XOS with prebiotic properties and 6.30% of ash. The concentrate of polyphenols was represented to a greater extent by ferulic acid (33.47%) with antioxidant activity up to 74.0%. The process of enzymatic hydrolysis demonstrated a significant change in the fractional composition of the extracted oxycinnamic acids, which make up the polyphenolic compounds of millet husk. In the polyphenol concentrate, the yield of ferulic acid increased by 19%, and that of gallic acid – by 2.5%, whereas the yield of chlorogenic acid decreased by 13%. The XOS concentrate mainly consisted of XOS fragments with prebiotic properties – up to 78% in absolutely dry matter. The fractional composition of the XOS concentrate revealed the presence of di-, tri-, tetra-, and pentaxylo-oligosaccharides. Xylotriose and xylotetrose prevailed in the KOS concentrates: 15.83 and 16.23%, respectively. The waste of enzymatic husk processing proved to be a concentrate of valuable dietary fiber that can be used as an independent product in the technologies of balanced and dietary nutrition.
 Conclusion. Millet husk is an excellent source of polyphenolic compounds with antioxidant and prebiotic properties and can be used in functional food production.