Antioxidant capacity and phytochemical content of 16 sources of corn distillers dried grains with solubles (DDGS)

Corn distillers dried grains with solubles (DDGS) is a co-product of the fuel ethanol industry that is an excellent source of energy, digestible amino acids, and digestible phosphorus. However, the antioxidant capacity and phytochemical content of DDGS and how it is influenced by production parameters is unknown. Therefore, 16 DDGS samples obtained from different ethanol production plants in the U.S. were characterized for antioxidant capacity, vitamin E, xanthophylls, and ferulic acid content and compared with corn. The antioxidant capacity of DDGS samples, measured using the 2,2-diphenyl-l-picrylhydrazyl (DPPH) assay, varied almost 2 folds among samples, but in all cases was more than 3 times that of corn. All DDGS samples had a considerably greater concentration of tocopherols and tocotrienols (lipid-soluble antioxidants) than corn. However, the relative concentrations among the tocopherols and tocotrienols tended to be similar to corn. The xanthophyll lutein was present in all DDGS samples and in all cases exceeded the content in corn. Zeaxanthin was detected in most samples. The total ferulic acid content of the DDGS samples was almost 3-fold greater than corn, but, as in corn, almost all was present in a bound form. However, the concentration of unbound (free) ferulic acid was more than 3 times the concentration found in the corn sample. Thus, DDGS is a rich source of phytochemical compounds and may provide antioxidant and health benefits beyond its macronutrient composition. However, differences in processing can greatly influence the phytochemical content and quality of DDGS. In particular, thermal abuse due to excessive heat used in drying may lead to lipid oxidation products that may have deleterious effects when incorporated into feeds.

Development of an in vitro protein digestibility assay mimicking the chicken digestive tract

It is difficult to obtain in vivo digestion kinetics data of high protein ingredients using chickens. Collecting kinetics data requires repeated sampling of digesta from the small intestine during the digestion process, which is not easily accomplished due to the anatomical structure of chicken digestive tract. An in vitro technique is proposed for measuring the digestion kinetics of protein sources fed to chickens. The method has a 30 min gastric and 3 h intestinal phase. Five hundred milligram crude protein (CP) equivalent of each meal sample (CP = % N × 6.25) was digested with pepsin (28,260 units) in 50 mL polyethylene centrifuge tubes for 30 min in a shaking water bath (150 strokes/min; 30 mm stroke length) at 41 °C. The 6.5 mL pancreatin was selected as the enzyme concentration for the intestinal phase, during which time 500 μL aliquots were collected at 0, 15, 30, 45, 60, 90, 120, 150, 180 and 240 min. Samples were diluted 1:820 with HCl and sodium acetate buffer, and then mixed with ninhydrin reagent (2:1) at 100 ± 2 °C for 15 min and spectrometric readings taken at 568 nm. To validate the assay, 5 replications of soybean meal (SBM), corn gluten meal (CGM), corn distillers dried grains with solubles (CDDGS), porcine meal (PCM), fish meal (FM) and casein (CA) were digested. The digestion data were modeled with PROC NLIN procedure, and the intra coefficient of variation (CV) assessed using PROC MEANS of SAS 9.4. The digestion values at 180 min were SBM 95 ± 4, FM 93 ± 3, PCM 68 ± 4, CGM 82 ± 3 and CDDGS 70 ± 2. Intra CV for SBM, CGM, CDDGS, PCM and FM were 5%, 5%, 12%, 10% and 2%, respectively. The estimated fractional digestion rates for SBM, CGM, CDDGS, FM and PCM were 0.023, 0.013, 0.009, 0.024 and 0.013, respectively. In conclusion, the proposed in vitro technique estimated the rate and extent of the digestion of CP for the meals with low intra CV.