Development and characterization of air-classified plasma-treated foxtail millet starch fractions as an alternative to native starch binder in biodegradable products.

Air classification, a dry fractionation method, is used to obtain starch fractions from foxtail millet. The obtained fractions were exposed to atmospheric cold plasma and used as raw material for biodegradable spoon production, replacing the conventional binder, corn starch. Different physicochemical, structural, rheological, and functional characteristics of starch fractions were assessed. The starch fractions were treated at 20 and 30 kV for 10 and 20 min. Plasma treatment at 30 kV for 20 min increased the apparent amylose content by 17%. It increased water absorption capacity by 15.1%, as shown by a stronger FTIR absorption band at 3310 cm-1, indicating greater hydrophilicity. All plasma-treated samples exhibited shear-thinning behavior. X-ray diffraction confirmed retention of the native A-type crystalline pattern, with decreased relative crystallinity after plasma exposure. Surface erosion and morphological alterations of starch granules were observed by scanning electron microscopy. Incorporation of plasma-treated starch fractions into biodegradable spoons significantly improved tensile strength (3.26 MPa) and elongation at break (8.77%) compared with the untreated control (1.67 MPa and 5.77%, respectively). The contact angle decreased from 79° to 49.5°, indicating improved surface wettability, and spoons prepared entirely from plasma-treated starch fractions degraded rapidly in soil within 10 days. FTIR spectra indicated that the native starch structure remained intact while stronger interactions developed between starch and protein components during spoon formation. The developed starch fractions exhibit considerable promise for manufacturing biodegradable cutlery, offering an environmentally sustainable alternative to conventional starch binders and expanding the industrial applications of value-added millet ingredients.