Comparative analysis of the physicochemical characteristics of kafirin proteins extracted from various grain sorghums and their distillers’ grains

Abstract: Sorghum is a globally significant cereal crop that can be a potential source of innovative plant proteins. The primary storage protein in grain sorghum is kafirin. This study aims to conduct a comparative analysis of the physicochemical and functional properties of kafirin proteins extracted from different types of sorghums, as well as their dried distillers’ grains (DDG), in order to understand the effect of sorghum type and fermentation process on protein properties.

Seven different types of whole grain sorghum, including white, red, black, and waxy varieties were sourced from a commercial supplier. A portion of each type of sorghum was used to produce Chinese baijiu, and the resulting DDG were collected. Both the original grains and DDG were ground into fine flours, and kafirin protein was extracted using the glacial acetic acid method. The protein content, SDS-PAGE profiles, molecular size distributions, secondary structure composition, surface hydrophobicity, in vitro protein digestibility, and functionality of the extracted proteins were characterized.

The extracted kafirins had protein content ranging between 75-85%. SDS-PAGE results showed that the kafirins from different types of sorghums had similar band profiles, but new bands in the range of 10-15 kDa were observed for the kafirins from DDG. The surface hydrophobicity of the kafirins from different types varied between 50-60 µg SDS/mg protein, and the fermentation process further altered the surface hydrophobicity to some extent. The kafirin from black sorghum DDG had slightly lower in vitro protein digestibility (around 74%) compared to that of other sorghum DDG (75-79%), which may be due to the much higher tannin content in the black variety.

This study provides fundamental knowledge of the protein properties associated with different sorghum genotypes and their distillers’ grains, which will aid in the future production and wider applications of sorghum proteins.