Cold Plasma-induced Changes in the Antinutritional, Nutritional, and Functional Properties of Air-classified Foxtail Millet (Setaria italica L.), Protein Fractions

Abstract

Foxtail millet is a nutritionally rich cereal with good adaptability to diverse agro-climatic conditions and was subjected to air classification to isolate a protein-rich fraction from the whole flour. Air classification using an air classifier (Hosokawa Alpine ATP 50; 5000 rpm; 0.3 kg h⁻¹) produced nutritionally distinct fractions. From 4.30 kg of feed, 2.470 kg of protein-rich fine fraction (approximately 57.44%) and 1.70 kg of starch-rich coarse fraction (approximately 39.53%) were recovered. Cold plasma (CP), a non-thermal method, was applied to the foxtail millet fine fraction at 20 kV for 10 min, resulting in greater reductions in antinutritional parameters. In the untreated and CP-treated foxtail millet protein fractions, respectively, tannins decreased from 19.49 ± 0.75 to 14.40 ± 0.83 mg TAE/100 g, phytates from 77.07 ± 0.99 to 64.65 ± 0.59 mg/100 g, oxalates from 8.32 ± 0.85 to 4.11 ± 0.97 mg/100 g, and saponins from 2.45 ± 0.90% to 1.71 ± 0.70%. Nutritional properties, bioactive compounds such as phenols and flavonoids, and functional and physical properties showed marginal increases after CP treatment. SEM images of the control whole foxtail millet flour, the foxtail millet protein fraction, and the CP-treated protein fraction showed morphological changes on the surface of the CP-treated flour. Principal component analysis of all measured attributes further confirmed that the three sample types formed distinct, non-overlapping multivariate clusters, verifying that air classification and cold plasma treatment produced reproducible, holistic changes rather than incidental variation. To our knowledge, this is the first study to combine dry (air-classification) fractionation with cold plasma treatment specifically for foxtail millet, and the resulting low-antinutrient, functionally enhanced protein fraction is a promising clean-label ingredient for gluten-free bakery products, extruded snacks, and other plant-protein-based product development.