Structural changes in kafirin extracted from a white type II tannin sorghum during germination

Kafirin proteins were extracted from a Sudanese cultivar of sorghum (Feterita). The extracted materials were characterized by SDS PAGE. Under non-reducing conditions as germination was progressing from 0 to 72 h, there was visually a decrease in β-kafirins whereas a small effect was observed on α-kafirins. The occurrence of interactions between tannins and kafirin might explain this behavior when compared to other cultivars. Thermogravimetric analysis (TGA) revealed that the first change in weight between room temperature and 100 °C was due to the loss of water. The protein extract started to degrade thereafter with the decomposition rate increasing with germination time. Fourier Transform Infrared (FT-IR) analysis showed that the secondary structure of kafirin was found to be mainly governed by α-helices with some β-sheets. Upon germination, there was a change in protein conformation, mainly an increase in α-helices. Scanning Electron Microscopy (SEM) showed that after extraction, kafirin proteins formed aggregated particles. This study is the first to show in the case of Feterita cultivar that upon germination, the physical properties of the kafirin proteins were significantly affected and relied on composition. This could shed some light on the effect of processing such as germination on sorghum kafirin proteins originated from Feterita.

► Kafirin has been extracted from sorghum grains germinated at 0, 24, 48 and 72 h.
► SDS PAGE confirmed the decrease in β-kafirin upon germination.
► The onset temperature of thermal degradation of kafirin decreased with germination time.
► The kafirin conformation was mainly governed by α-helices and its content increased upon germination.
► Scanning electron microscopy revealed that kafirin proteins appeared as aggregated particles irrespective of germination time.