Urea-cysteine based extraction of densely crosslinked proteins from sorghum distillers grains with high yield and quality

Abstract

A urea-cysteine based system is developed to extract densely crosslinked sorghum proteins from sorghum distillers grains with high efficiency and quality. Due to the high crosslinking degrees, sorghum proteins are expected to possess better tensile properties and aqueous stabilities than common proteins, thus become a promising candidate to replace the unsustainable petroleum products. However, due to the long-standing difficulty in dissolution of densely crosslinked proteins, to extract sorghum proteins with high efficiency and quality for satisfactory properties in end products has not been achieved by previous methods In this paper, a urea-cysteine based system is used to replace the most widely used ethanol based system. The urea-cysteine based system endows sorghum proteins with high purity and yield, which are 14% and 42% higher than those from the ethanol based system. Based on amine and thiol group analysis, the urea-cysteine based system provides sorghum proteins with preserved peptide backbones, full breakage of disulfide bonds for linear structures and sufficient thiol groups for re-oxidation. Due to such unique structures and thus regular arrangement of protein molecules during film casting, sorghum protein films from the urea-cysteine based system have crystallinity 21% higher than those from the ethanol based system. Tensile properties and water-vapor-barrier properties of sorghum protein films are improved by 27% and 28% compared to the ethanol based system. Sorghum protein films derived from sorghum distillers grains are first reported and their tensile properties are better than those of all sorghum protein films developed previously. Quantified effects of preservation of protein peptide backbones and recovery of disulfide bonds on tensile strength are also compared. With the unique structures, sorghum proteins from the urea-cysteine based system have great potential to achieve excellent properties in various applications, such as films and fibers, which account for a total market share of over $100 billion worldwide.