Analysis of Kafirin Content in Sorghum Sprouts Cultivated in a Temperate Climate

Previous studies on kafirins in sorghum (Sorghum bicolor Moench) have focused mainly on grain and sprouts grown under tropical and subtropical climate conditions, while data on the content and fractional composition of kafirins in sorghum sprouts cultivated in temperate climates are scarce. In particular, the influence of the northern growing conditions, characteristic of Central Europe, on sorghum storage proteins has not yet been described, despite the fact that sorghum is currently cultivated in Poland. This study aimed to determine the total kafirin content and the distribution of α-, β-, and γ-kafirin fractions in sprouts of white and red sorghum grown under temperate climate conditions in Poland. Six-day-old sprouts were freeze-dried and extracted using a Tris-HCl/SDS/β-mercaptoethanol buffer. Kafirin content was quantified using the Bradford assay, SDS-PAGE, and HPLC, with method validation performed for accuracy, precision, and linearity. Total kafirin content ranged from 5.5 to 7.0 g/100 g dry matter (DM), with α-kafirin as the predominant fraction (4.2–5.0 g/100 g DM), followed by β-kafirin (0.5–1.0 g/100 g DM) and γ-kafirin (0.2–0.6 g/100 g DM). Sprouts of red sorghum varieties showed significantly higher total kafirin levels and a greater proportion of the γ-fraction, which may be associated with differences in protein structural properties and could suggest potential bioactivity, as indicated by previous literature. However, no direct functional or bioactivity assays were performed in this study. Statistical analysis revealed significant differences among selected sorghum varieties in total kafirin content and the proportion of the γ fraction (p < 0.05), with α being the dominant fraction in all tested samples. These results provide, for the first time, detailed data on the kafirin composition of sorghum sprouts grown in a temperate climate and address a key gap in the literature concerning the effect of environmental conditions on sorghum storage proteins. The findings support further research on the use of sorghum sprouts as a raw material for functional foods, protein-enriched products, and animal feed under European growing conditions.