Alkaline fractionation and enzymatic saccharification of wheat dried distillers grains with solubles (DDGS)

Abstract

The complete utilisation of Dried Distillers Grains with Soluble (DDGS) requires effective pretreatment strategies aiming to increase the enzymatic digestibility of cellulose and improve its conversion to fermentable sugars. To this end, the effect of different NaOH concentrations (0-5%, w/v) and temperature (30-121 o C) on the fractionation of DDGS to its main components (cellulose, hemicellulose, proteins) was evaluated. As the NaOH concentration and temperature increased, the total sugar content of the pretreated DDGS solids progressively increased to a maximum of ~88%. At 121 o C and 5% NaOH, the DDGS solid residue consisted primarily of glucose (~53%), a 5-fold increase compared to the original DDGS, reflecting the presence of cellulose, and to a lesser extent by xylose (~25%) and arabinose (~10%) reflecting the presence of hemicellulose. Approximately 83% of the initial hemicellulose and 79% of the protein contents were removed into the liquid fraction during alkaline pretreatment. The enzymatic digestibility of the pretreated DDGS solids by the Accellerase® 1500 cellulase enzyme was significantly improved, resulting in a 3.6 fold increase in glucose yield compared to untreated DDGS. Mass balance analysis demonstrated that the proposed process scheme recovers the majority of the key DDGS components (cellulose, hemicellulose, proteins) in an efficient manner with relatively low losses, and provides a viable approach for the valorisation of DDGS.

Proteins in dried distillers' grains with solubles: A review of animal feed value and potential non‐food uses

“…First, DDGS is often subjected to hexane extraction to remove oil. After solid and liquid filtration, the residual DDGS is submerged into solvents aforementioned at certain temperatures for specific times, and then precipitation or centrifugation is conducted for protein recovery (Chatzifragkou et al, 2016; Gupta et al, 2016; Wang et al, 2009; Zaini et al, 2019). Gupta et al (2016) evaluated the differences in zein protein recovery using 13 different solvents (isopropanol, isoamyl alcohol, n‐butanol, isobutanol, 2,3‐butanediol, 1,4‐butanediol, tetrahydrofuran, 1,3‐dioxolane, 1,4‐dioxane, acetic acid, lactic acid, [emim]Ac, and [emim]Br) and found that isopropanol resulted in the highest extraction efficiency of 75%.…”

“…Moreover, the acetic acid extraction protocol led to 98.9% kafirin purity, which is significantly higher than HCl–ethanol and NaOH–ethanol treatments (Wang et al, 2009). In the case of wheat‐DDGS, approximately 79% of protein content has been extracted into the liquid fraction using 5% NaOH treatment (Zaini et al, 2019).…”

“…To extract and valorize the valuable protein fraction of DDGS, various physicochemical strategies have been proposed. The conventional method of alkaline pretreatment increased the enzymatic hydrolysis of cellulose with 79% protein extraction efficiency (Zaini et al, 2019). Compared with individual NaOH pretreatment, the ultrasound‐assisted process with NaOH resulted in more significant protein and essential AA contents in the extract (Gu et al, 2019).…”

Recovery of Nitrogen from Low-Cost Plant Feedstocks Used for Bioenergy: A Review of Availability and Process Order

“…Several protein extraction methodologies and conditions have been reported for integrated biorefineries. , Chemical methods include alkaline extraction, , aqueous ammonia (AFEX) extraction, , buffer extraction, organic solvent extraction, and combinations of these methods. , Alkaline extraction is commonly used for extracting proteins from agriculture residues, deoiled seedcakes, and DDGS with protein recoveries of 82–91.1%, 15–36%, and 60–79%, respectively. − The efficacy of protein extraction using chemical methods depends on the nature of the biomass, solid-to-solvent ratio, temperature, pH, and process time . A recent review by Kumar et al summarized the effects of the sample-to-solvent ratio, alkali concentration, time, and temperature for several protein extractions from plant .…”

“…A large amount of nonproteinaceous compounds are also present in the protein precipitate . Extraction of proteins from oilseed cakes has been done using hydrothermal and enzyme-assisted processes, followed by ultrafiltration and isoelectric precipitation, electrolyzed water treatment, alkaline precipitation, or acidic precipitation. ,, Extraction of proteins from DDGS and food wastes has been reported using alkaline, hydrothermal, and enzyme-assisted extraction, or coupling AFEX pretreatment and enzymatic extraction followed by acid precipitation …”