Methods to recover value-added coproducts from dry grind processing of grains into fuel ethanol

Nutritional value of high protein ingredients fed to growing pigs in comparison to commonly used protein sources in swine diets

Two experiments were conducted to test the hypothesis that two high protein dried distillers with solubles and yeast mass added (GDDY) products fed to growing pigs had comparable amino acid (AA) digestibility and metabolizable energy (ME) to feeds commonly used in swine diets. In experiment 1, seven barrows with an initial body weight (BW) of 25 ± 0.8 kg were fitted with a simple T-cannula at the distal ileum to allow for digesta collection. Experimental diets were N-free diets and six cornstarch-based diets containing six ingredients as the sole source of AA: spray dried GDDY, ring dried GDDY, corn distillers dried grains with solubles (DDGS), soybean meal (SBM), enzymatically treated soybean meal (ESBM), and fish meal (FM) provided at 4% of BW. The experiment was conducted as a 7 × 7 Latin square design with seven collection periods of 7 d (5 d adaptation and 2 d ileal digesta collection). In experiment 2, a total of 28 barrows (28.8 ± 1.4 kg BW) were used in a two-period switch-back design with seven diets and four replicate pigs in each period (n = 8 reps per diet). Experimental diets were a corn-based basal diet and six corn-based diets containing spray dried GDDY, ring dried GDDY, DDGS, SBM, ESBM, and FM. Fecal and urine samples were collected using the marker-to-marker approach for 5 d after 7 d of adaptation to determine ME concentration. Overall, standardized ileal digestibility (SID) values were within the mean ± SD of NRC (2012) values for all ingredients evaluated. The SID of AA was greater (P < 0.05) in ESBM than the other protein feedstuffs (90.09% vs. 78.71%-81.51%). There were no significant differences in SID of AA (P > 0.05) in SBM, FM, spray dried GDDY, and ring dried GDDY (81.49%, 78.71%, 81.52%, and 79.20%). With respect to the most common first limiting AA for swine, the SID of Lys was greater (P < 0.05) in spray dried GDDY than ring dried GDDY and DDGS (83.56% vs. 77.33% and 68.53%, respectively). There were no significant differences (P > 0.05) for ME in corn (3,313 kcal/kg), ESBM (3,323 kcal/kg), and FM (3,454 kcal/kg) when compared with spray dried GDDY and ring dried GDDY (3,995 and 3,442 kcal/kg respectively). However, spray dried GDDY had greater DE and ME when compared to SBM. Collectively, this study demonstrates that GDDY products have an AA profile and digestibility comparable to SBM; ME in GDDY products is not different from corn. Therefore, GDDY has the potential as a feed ingredient for pigs, which could provide an alternative source of protein and energy in swine diets.

Corn distillers solubles as a novel bioresource of bioactive peptides with ACE and DPP IV inhibition activity: characterization, in silico evaluation, and molecular docking

This study aimed to investigate the biological potential of underutilized and low-value corn distillers solubles, containing a unique unexplored blend of heat-treated corn and yeast proteins, from the bioethanol industries, by bioinformatic and biochemical approaches. Protein hydrolysates were produced by applying four commercially accessible proteases, among which alcalase provided the best results in terms of yield, degree of hydrolysis, molecular weight, number of proteins, bioactive peptides, and deactivation against anti-angiotensin I-converting enzyme (ACE) and anti-dipeptidyl peptidase IV (DPP IV). The optimal conditions to produce anti-ACE and anti-DPP IV peptides were using alcalase for 10.82 h and an enzyme : substrate ratio of 7.90 (%w/w), with inhibition values for ACE and DPP IV of 98.76 ± 1.28% and 34.99 ± 1.44%, respectively. Corn (α-zein) and yeast (glyceraldehyde-3-phosphate dehydrogenase) proteins were mainly suitable, upon enzymolysis, for the release of bioactive peptides. The peptides DPANLPWG, FDFFDNIN, WNGPPGVF, and TPPFHLPPP inhibited ACE more effectively as verified with binding energies of -11.3, -11.6, -10.5, and -11.6 kcal mol^-1, respectively, as compared to captopril (-6.38 kcal mol^-1). Compared with the binding energy of sitagliptin (-8.6 kcal mol^-1), WNGPPGVF (-9.6 kcal mol^-1), WPLPPFG (-9.8 kcal mol^-1), LPPYLPS (-9.7 kcal mol^-1), TPPFHLPPP (-10.1 kcal mol^-1), and DPANLPWG peptides (-10.1 kcal mol^-1) had greater inhibition potential against DPP IV. The peptides impeded ACE and DPP IV majorly via hydrophobic and hydrogen linkage interactions. The key amino acids TYR⁵²³, GLU³⁸⁴, and HIS³⁵³ were bound to the catalytic sites of ACE and GLN⁵⁵³, GLU²⁰⁶, PHE³⁶⁴, VAL³⁰³, and THR³⁰⁴ were bound to the DPP IV enzyme. The PHs can be used as ingredients in the feed or food industries with possible health advantages.

Changes in Bacterial Populations and Their Metabolism over 90 Sequential Cultures on Wheat-Based Thin Stillage

Wheat-based thin stillage (W-TS) is a liquid co-product of wheat fermentation for ethanol production, which typically contains substantial amounts of glycerol. Two-stage fermentation, via endemic microorganisms, can be used in processes to convert this compound to more valuable products and simplify the enrichment process through the clarification of the medium and concentration of particles as a protein-rich concentrate. We recultured bacteria 90 times (72 h at 37 °C) on fresh W-TS to determine the stability of the culture and metabolic processes. Next-generation sequencing of W-TS revealed the presence of a predominant Lactobacillus community that rapidly displaced competing microorganisms (e.g., Pediococcus) in subsequent fermentations. These organisms produced bacteriocins (e.g., helveticin J, interpreted through the presence of bacteriocin genes) and acidified the fermentation broth (through the production of succinic acid: 1.7 g/L, lactic acid: 1.8 g/L, and acetic acid: 4.1 g/L). Furthermore, the microbial community produced cobalamin (inferred through sequencing) and converted glycerol (10 g/L reduced to 3.5 g/L after 72 h) to 1,3-propanediol (6.1 g/L after 72 h). Altogether, Lactobacilli were identified as the predominant endemic microorganisms in W-TS after the first 10 cultures. The community was stable and provided a novel approach to increase the value of organic solutes in W-TS.

Production of Protein Concentrate and 1,3-Propanediol by Wheat-Based Thin Stillage Fermentation

Fermentation of wheat with yeast produces thin stillage (W-TS) and distiller's wet grains. A subsequent fermentation of W-TS (two-stage fermentation, TSF) with endemic bacteria at 25 and 37 °C decreased glycerol and lactic acid concentrations, while 1,3-propanediol (1,3-PD) and acetic acid accumulated with greater 1,3-PD and acetic acid produced at 37 °C. During TSF, W-TS colloids coagulated and floated in the fermentation medium producing separable liquid and slurry fractions. The predominant endemic bacteria in W-TS were Lactobacillus panis, L. gallinarum, and L. helveticus, and this makeup did not change substantially as fermentation progressed. As nutrients were exhausted, floating particles precipitated. Protein contents of slurry and clarified liquid increased and decreased, respectively, as TSF progressed. The liquid was easily filtered through an ultrafiltration membrane. These results suggested that TSF is a novel method for W-TS clarification and production of protein concentrates and 1,3-PD from W-TS.

Conversion of Thin Stillage Compounds Using Endemic Bacteria Augmented with Lactobacillus panis PM1B

A consortium of organisms, endemic in wheat-based thin stillage (W-TS), obtained from a commercial ethanol production converts glycerol to 1,3-propanediol (1,3-PD) and lactic acid to acetic acid. We sought to improve conditions for 1,3-PD and acetic acid production to be used in future studies of industrial isolation of these compounds from two-stage fermentation. Occasionally, stillage fermentation proceeded slowly, but an inoculum of Lactobacillus panis PM1B augmented both fermentation rate and extent. Fermentation rate and product yield were enhanced by adjusting pH to 5 daily and adding glucose and glycerol (molar ratio 0.1:1), freeze-dried W-TS, and vitamins (B₂, B₃, and B₁₂). 1,3-PD and 3-hydroxypropionaldehyde (3-HPA) did not inhibit 1,3-PD production during fermentation. Moreover, agitation did not improve fermentation rate or extent. Corn sugar was a suitable substitute for glucose. Fermentation was performed at both 20 and 150 L with 1,3-PD production of 2% (w/v, 20 g/L) being routinely achieved or exceeded.