Optimization and Characterization of Dried Distiller Grains With Solubles as a Sustainable Protein Isolate

The increasing demand for sustainable and high-quality protein sources has driven research into the efficient extraction and characterization of proteins from various plants and industrial by-products. Dried distillers grains with solubles (DDGS) is a rich source of protein with potential applications in food and animal feed; however, the structural and nutritional properties of DDGS require further elucidation compared with those of soy protein isolate (SPI).

Thus, this study aimed to optimize protein extraction from DDGS using response surface methodology, yielding a protein yield of approximately 23%. The extracted proteins were characterized by proximate analysis, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) to assess structural integrity, thermogravimetric analysis, differential scanning calorimetry, Fourier-transform infrared spectroscopy, and amino acid profiling. Comparative analyses with SPI were conducted to evaluate their structural, thermal, and nutritional differences.

The optimized extraction conditions included a 2-hour extraction time, a solid-to-liquid ratio of 1:10, 1 M sodium hydroxide (NaOH), and 60% ethanol. The crude protein content increased significantly from 24.94% in raw DDGS to 65.21% in the isolate. SDS-PAGE revealed intact globular protein bands in SPI, whereas DDGS proteins showed fragmentation, likely due to denaturation and interactions with fiber. Thermal analysis indicated that DDGS proteins possessed higher heat resistance and thermal stability than SPI. Amino acid analysis demonstrated the superior essential amino acid profile of SPI, which was rich in leucine, lysine, phenylalanine, and etc. In contrast, DDGS proteins contained valuable amino acids, including glutamic acid, aspartic acid, and branched-chain amino acids, making the DDGS proteins suitable for ruminant diets. These structural and compositional differences reflect the respective suitability of these sources for food versus feed applications.

This study highlights the effectiveness of optimized extraction techniques for isolating high-protein concentrates from DDGS and emphasizes the distinct characteristics of DDGS proteins compared with SPI. While SPI remains ideal for nutritional formulations requiring high purity and amino acid completeness, DDGS proteins offer a sustainable alternative for livestock nutrition, especially in ruminant diets. These findings support the broader utilization of DDGS as an economical and environmentally sustainable protein source.