Cascade extraction of sorghum proteins from distillers grains for high-quality biobased materials

Abstract

Sorghum distillers grains contain enriched proteins, which offer potential applications beyond traditional livestock feed. For the first time, major proteins from sorghum distillers grains were individually extracted and transformed into high-quality protein films via an aqueous system. Sorghum distillers grains are by-products of bioethanol production from sorghum grain. However, extracting sorghum proteins from distillers grains poses challenges due to protein densification and denaturation during ethanol production's distillation and drying phases. The increased non-covalent interactions among protein molecules further complicate their extraction. Moreover, previously, only the kafirin part, accounting for 55 % of sorghum proteins, was extracted while the glutelin, which has a higher molecular weight than kafirin and accounts for about 35 % of sorghum proteins, was left in distillers grains. Kafirin and glutelin from sorghum distillers grains were successfully extracted with a high yield in this work. The extraction technology individually separated kafirin and glutelin from sorghum distillers grains, providing a high extraction yield of up to 83 % and protein purity of 93 %. Besides, more kafirin subunits rich in cysteine were obtained by incorporating the oxidation step. An aqueous system was also developed to regenerate proteins and fully stretch both kafirin and glutelin simultaneously, improving interactions between protein molecules, enhancing molecular entanglement, and inducing ordered protein structures. As a result of protein extraction and dissolution techniques, tough and flexible protein films were developed from sorghum distillers grains.