Impact of germination on barley protein, transformations and microstructural alterations

This study evaluates the morphological and structural changes in barley protein during germination. Ungerminated grains exhibited a well-defined structural organization, with intact pericarp, aleurone layer, and protein bodies, showing no evidence of hydrolysis. Starch granules were embedded in a compact protein matrix. After germination, cell gaps appeared, the pericarp partially disintegrated, and inner layers were exposed. The CIE Lab analysis revealed a progressive degradation and spatial redistribution of the protein matrix during germination. The structures became less compact, and the aleurone layer began to break down. Protein content significantly decreased, from 10.41% in ungerminated grains to 7.33% after 6 days of germination. The area of the protein matrix of the ungerminated sample was 12.44% greater than after 3 and 6 days of germination. The electrophoretic profile and the densitometry revealed progressive degradation of D-hordeins, C-hordeins, and γ-hordeins, although this degradation was not reflected in the amino acid content; most amino acids showed no significant changes during germination. However, methionine and tyrosine significantly increased, while proline decreased after 6 days of germination. Germinated samples contained essential amino acids, mostly meeting FAO/WHO/UNU standards, except for methionine and lysine. Fourier Transform Infrared Spectroscopy (FTIR) analysis indicated a decrease in transmittance as germination progressed. The proportion of β-turns significantly decreased from 36.24% to 29.18%, while α-helix content fluctuated, initially decreasing and then increasing. The proportions of β-sheets and random coils increased in 6-day germinated samples, reaching maximum values of 27.99% and 22.63%, respectively. Barley germination induces significant transformations in protein structure. These changes could influence the functional properties of germinated barley, opening new possibilities for its use in the food industry and other applications. • Protein content in barley significantly decreased from 10.41% to 7.33% after 6 days of germination • D-hordeins, C-hordeins, and γ-hordeins showing progressive degradation with germination time. • Germination caused cell gaps, pericarp disintegration, and aleurone layer rupture. • Methionine and tyrosine levels increased with germination, while proline decreased. • Germination altered protein structures: β-turns decreased, while β-sheets and coils increased.