Comparison of glutelins characteristics among foxtail millet varieties: Functional, physico-chemical, and structural modifications induced by hydrothermal treatment

This research evaluated the functional, physico-chemical and structural characteristics of glutelin, a major storage protein, extracted from four Chinese foxtail millet (Setaria italica) varieties (ZZ10, Y18, CH8 and CH6) under raw (GR) and hydrothermally treated (GB) (boiled at 95-100 °C for 15 min) conditions. The purity of glutelin fractions ranged from 76.01 % to 77.56 %, with significant varietal differences in amino acid composition, thermal stability, solubility and surface properties. Glutamic acid was the predominant amino acid, and hydrothermal treatment enhanced the availability of key amino acids, particularly glutamic acid, leucine and alanine. The GB treatment reduced solubility, zeta potential, and water absorption capacity while increasing particle size and disulfide bond content, reflecting heat-induced denaturation and aggregation. Fourier-transform infrared spectroscopy (FTIR) analysis revealed reduced α-helical content and increased β-sheet structures, indicating structural rearrangements. Scanning electron microscopy (SEM) showed compact, aggregated glutelin structures in GB samples, with CH6 and CH8 being most affected. ZZ10 maintained superior solubility, thermal stability, and structural integrity while CH6 and CH8 were highly susceptible to heat-induced changes. X-ray diffraction (XRD) and intrinsic fluorescence confirmed glutelin unfolding, reduced crystallinity, and exposure of hydrophobic residues post-boiling. These findings demonstrate that ZZ10 exhibits superior thermal stability and functional properties, making it suitable for thermally processed foods, while CH6 and CH8 are more susceptible to heat-induced structural changes, limiting their functionality in such applications. The study provides crucial insights for optimizing millet-based foods through varietal-specific protein behavior.