Nutritional Characteristics of Corn Distillers Dried Grains with Solubles ...

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sion-fed cecectomized rooster assay (Parsons et al., 1992). For the rooster digestibility assay, 30 g of the DDGS and grains samples were tube-fed to 4 roosters, ...
Nutritional Characteristics of Corn Distillers Dried Grains with Solubles as Affected by the Amounts of Grains Versus Solubles and Different Processing Techniques C. Martinez-Amezcua,* C. M. Parsons,*1 V. Singh,† R. Srinivasan,† and G. S. Murthy† *Department of Animal Sciences, and †Department of Agricultural Engineering, University of Illinois, Urbana 61801 ABSTRACT Experiments were conducted to evaluate the nutritional value of corn distillers dried grains with solubles (DDGS) and its components of grains and solubles, the effect on amino acid digestibility of autoclaving DDGS with different proportions of wet grains:solubles, and the effect of several new processing technologies on the nutritional value of DDGS for poultry. In the latter experiments, corn was processed under laboratory conditions to produce ethanol and DDGS by using the conventional dry-grind process and compared with 2 modified dry-grind corn processes. Modified dry-grind corn processes consisted of wet quick germ, quick fiber (QGQF process) and dry degerm defiber (3D process) fractionation of corn to recover the germ and pericarp fiber prior to fermentation. In another process, a commercial DDGS sample was subjected to an Elusieve method to remove fiber and increase the protein content. Freeze-dried solu-

bles were higher in total P but lower in CP than in the grains and DDGS. Digestibilities of several amino acids in the freeze-dried grains and solubles were higher than those for DDGS, particularly for Lys. Autoclaving reduced the digestibility of amino acids in DDGS, and this effect was not influenced by the proportion of grains:solubles. The QGQF and 3D processes increased the protein and reduced the fat and total dietary fiber content in DDGS. Total P was increased by the QGQF process, but was reduced by the 3D process. The Elusieve process increased the protein, amino acids, and fat, and decreased the total dietary fiber content of DDGS from 34.5 to 19.7% on a DM basis. None of the processing technologies had a significant effect on DDGS amino acid digestibility. The results of this study indicated that the nutritional value of DDGS can be influenced greatly by the proportion of grains vs. solubles and by processing technologies.

Key words: distillers dried grains with solubles, processing method, poultry 2007 Poultry Science 86:2624–2630 doi:10.3382/ps.2007-00137

INTRODUCTION Dry-grind ethanol production is growing in the United States and is expected to continue to increase for several years (Renewable Fuels Association, 2006). Most of this increase in ethanol production capacity is expected to come from new dry-grind corn plants. In the dry-grind process, corn is ground and mixed with water to form a slurry. The slurry is then cooked and starch in the slurry is liquefied, saccharified (hydrolyzed), and fermented to produce ethanol. Nonfermentable components in corn (germ, fiber, protein) are recovered at the end of the process as distillers dried grains with solubles (DDGS). Because of its high fiber content, DDGS has traditionally been fed primarily to ruminants. Because of the large increase in DDGS production, there is an interest in feeding more DDGS to poultry, in developing new processing

©2007 Poultry Science Association Inc. Received March 30, 2007. Accepted August 7, 2007. 1 Corresponding author: [email protected]

technologies for DDGS to increase its nutritional value for nonruminant animals, and in producing new products for market diversification. New processing and fractionation technologies are being developed for DDGS to recover nonfermentables (germ and fiber) prior to the dry-grind process. These technologies include the quick germ, quick fiber method (QGQF; Singh et al., 1999) and the dry degerm defiber method (3D; Murthy et al., 2006), which recover germ and pericarp fiber at the beginning of the dry-grind process prior to fermentation. The QGQF method involves fractionation of corn in an aqueous medium (Singh et al., 1999), and the 3D method involves dry fractionation of corn (Murthy et al., 2006). Another technology, called Elusieve, which removes fiber from DDGS, has recently been developed (Srinivasan et al., 2005). The Elusieve process includes fractionation of DDGS to remove fiber by sieving and air classification. The nutritional value of DDGS can be influenced by many factors. For example, the type of drying conditions can affect P bioavailability and amino acid digestibility, particularly Lys digestibility (Martinez Amezcua et al.,

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2007). The amounts of grains vs. solubles in DDGS could also possibly affect its nutritional value for poultry. In addition, the new technologies mentioned could have an effect on the nutritional value of the DDGS produced. The first objective of this study was to determine the nutrient composition and digestibility of amino acids in DDGS and its components of grains and solubles. In addition, the effect of autoclaving DDGS containing different amounts or proportions of grains and solubles was evaluated. The second objective was to determine the nutrient composition and digestibility of amino acids for several DDGS samples produced by using these new processing technologies.

MATERIALS AND METHODS General Procedures All sample analyses were performed on a thoroughly mixed batch of each feed ingredient. Samples were analyzed for DM (method 930.15; AOAC International, 2006), ash (method 942.05; AOAC International 2006), CP (method 990.03; AOAC International, 2006), crude fat (method 920.39; AOAC International, 2006), and total P (methods 965.17 and 985.01 modified; AOAC International, 2006). The CP analyses were performed by the University of Missouri Experiment Station Laboratories (Columbia, MO). The total P and crude fat analyses were performed by Eurofins Scientific Inc. (Des Moines, IA). Total dietary fiber was analyzed according to the method proposed by Prosky et al. (1984), and the soluble and insoluble fractions of total dietary fiber were analyzed by the method of Prosky et al. (1988). True amino acid digestibility was determined for DDGS samples by using the precision-fed cecectomized rooster assay (Parsons et al., 1992). The DDGS samples and excreta were analyzed for amino acids at the University of Missouri Experiment Station Laboratories [method 982.30 E (a, b, c); AOAC International, 2006]. Fatty acids in feed, including conjugated linoleic acid (CLA), were analyzed by using the method of Sukhija and Palmquist (1988).

Experiment 1: Composition and Amino Acid Digestibility of Commercial Samples of DDGS and Grains and Solubles Fractions Samples of commercial DDGS, wet grains (no solubles), and solubles were obtained from the same commercial ethanol plant. The DDGS sample was analyzed as received, and the grains and solubles fractions were freezedried prior to analysis. The DDGS, grains, and solubles fractions were analyzed for DM, and all the samples were analyzed for gross energy, crude fat, CP, ash, P, and total amino acids as described previously. Digestibility of amino acids was also determined by using the precision-fed cecectomized rooster assay (Parsons et al., 1992). For the rooster digestibility assay, 30 g of the DDGS and

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grains samples were tube-fed to 4 roosters, and for the freeze-dried solubles, 15 g of mixed with corn (50:50 ratio) was fed to 4 roosters to facilitate the tube-feeding.

Experiment 2: Effect of the Grains: Solubles Ratio and Autoclaving This experiment was conducted to evaluate the effect of different proportions of grains:solubles on the amino acid digestibility of DDGS and the susceptibility of the protein, particularly Lys, to heat damage from autoclaving. The solubles contained a large amount of reducing sugars and could increase the susceptibility of the DDGS to Maillard reactions during the drying process. Freezedried grains and solubles were mixed together in ratios of 62:38, 67:33, and 72:28 and 30 g of each was tube-fed to 5 different individually caged cecectomized roosters. In addition, each of the mixtures was autoclaved at 121°C and 105 kPa for 45 min, and 30 g of each sample was tube-fed to 5 cecectomized roosters. The normal ratio of grains to solubles in commercial DDGS is approximately 67:33. The amino acid digestibility of the 6 DDGS samples was determined according to Parsons et al. (1992).

Experiment 3: Nutrient Composition and Amino Acid Digestibility of DDGS Samples Processed Under Different Conditions For this experiment, corn was processed by using the conventional dry-grind, QGQF, 3D, and Elusieve processes. For the conventional dry-grind, QGQF and 3D processes, a yellow dent corn hybrid grown at the Agricultural Engineering Research Farm, University of Illinois at Urbana-Champaign, was used. The hybrid was field-dried for this study to approximately 15% moisture content and combine harvested. Corn samples were handcleaned to remove broken corn and foreign material, packaged in plastic bags, and stored at 4°C until processing. Whole-kernel moisture content was measured by using a 103°C conventional oven method (AACC, 2000; method 44-15A). Enzymes α-amylase (9000-85-5) and amyloglucosidase (9032-08-0) were obtained from SigmaAldrich Co. (St. Louis, MO). For the Elusieve process, commercial DDGS samples were obtained from a Midwestern dry-grind corn plant. Conventional Dry-Grind Process. Conventional drygrind processing was done as described by Murthy et al. (2006). Corn (1,000 g) was milled at 500 rpm in a crossbeater mill (model MHM4, Glen Mills Inc., Clifton, NJ) equipped with a 2-mm round-holed sieve. Moisture content of the milled corn was analyzed by using a 2-stage conventional oven method (AACC, 2002), and milled corn (500 g, DM basis) was mixed with water at 60°C to form a 25% solids mash. The mash was liquefied with 2.8 mL of α-amylase for 90 min in a water bath maintained at 90°C. After adjusting the mash pH to 4.2 by using 1.0 N sulfuric acid, the mash was subjected to simultaneous saccharification and fermentation as described in the section below. Liquefied mash was cooled to 30°C and ad-

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justed to 4.2 pH by using 1.0 N sulfuric acid. The mash was saccharified by adding 2.8 mL glucoamylase. Simultaneously, mash was inoculated with 0.022 g of active dry yeast/g of dry solids (Fleischmann’s Yeast, Fenton, MO). The (NH4)2SO4 was added to provide 500 mg/kg of free amino nitrogen. Simultaneous saccharification and fermentation were performed at 30°C for 60 h with continuous agitation at 50 rpm. 3D Process. A 1,000-g sample of corn was tempered to a moisture content of 22.5% for 18 to 20 min. The tempered corn was passed through a horizontal drum degerminator, which impacts and abrades the corn, resulting in partial separation of germ and fiber from the endosperm. The product was then dried for 2 h at 49°C to approximately 15% moisture. The dried material was processed 4 times through a roller mill and sieved over a 10-mesh sieve. The germ and fiber fractions that were retained on the sieve were separated by aspiration. The remaining milled fraction (after germ and pericarp fiber removal) was liquefied and fermented by using the conventional dry-grind process. QGQF Process. The QGQF process was done as outlined by Singh et al. (1999). The QGQF procedure was modified slightly to maintain the specific gravity of the slurry for recovery of germ and fiber. The modifications included addition of 3 mL of α-amylase and incubation of the slurry for 4 h after soaking and coarsely grinding the corn kernels. The remaining slurry (after germ and fiber removal) was liquefied and fermented by using the conventional dry-grind process. The DDGS samples from the conventional dry-grind, 3D, and QGQF processes were dried for 3 d at 60°C. The 3 samples were then tube-fed to 4 cecectomized roosters to estimate amino acid digestibility as described previously. Elusieve Process. The DDGS sample was sieved (model LS188333, Sweco Vibro-Energy Separator, Los Angeles, CA) and air classification was used to fractionate the commercial DDGS sample with a 234-␮m sieve as described by Srinivasan et al. (2005). The sieved material (material passing through the 234-␮m sieve) was collected and called Elusieve pan DDGS. This Elusieve pan DDGS was then tube-fed to 4 cecectomized roosters to estimate amino acid digestibility. Statistical analyses of the amino acid digestibility coefficients in experiments 1 to 3 were conducted by using ANOVA for completely randomized experiments with SAS computer software (SAS Institute, 1990). Differences among treatment means were determined by using the least significant differences test (SAS Institute, 1990), and differences among means were considered significant at P < 0.05.

RESULTS AND DISCUSSION For experiment 1, the solubles contained a lower level of CP than the grains but substantially higher levels of fat, ash, and P (Table 1). Total amino acid levels in the solubles were generally lower than those in the grains

and slightly lower than those in the DDGS. An exception was Lys, which was higher in the freeze-dried solubles than in the DDGS. The latter exception resulted because of the low level (0.5%) of Lys in the DDGS. This lower level of Lys may have been due to heat damage of the DDGS during drying in the commercial plant because the DDGS had a very dark brown color (Martinez Amezcua and Parsons, 2007). Digestibility of amino acids was generally highest for the grains, with the solubles having higher digestibility than the DDGS for several amino acids. The digestibility of Lys was much higher in the freeze-dried grains and solubles than in the DDGS. Again, this difference likely was mainly due to heat damage during the drying of the DDGS, because drying temperatures may be as high as 621°C (US Grains Council, 2007). Autoclaving DDGS for 45 min at 120°C in experiment 2 reduced the digestibility of amino acids (Table 2). The decrease was expected for Lys, which was the amino acid that was most affected. Unexpectedly, however, the digestibility of all other amino acids was also generally reduced by autoclaving. The large decrease for Lys was expected because of the Maillard, or browning, reaction but this reaction usually has little, or much less, effect on most other amino acids. The effect of autoclaving on amino acids other than Lys may be due to the formation of large amounts of Maillard reaction products, which have been shown to interfere with the absorption of amino acids in general and which can also reduce the efficiency of proteolytic enzymes in cleaving peptide bonds near the structurally altered Lys (Ersbersdobler et al., 1981; Moughan and Rutherford, 1996). The effects of autoclaving were similar for the DDGS containing different amounts of grains vs. solubles. These results were somewhat unexpected, particularly for Lys. It was expected that the adverse effects of autoclaving on Lys digestibility would be greater as the amount of solubles increased, because the solubles contain large amounts of reducing sugars that would be potential substrates for the Maillard reaction (Wu, 1994). The nutrient composition of DDGS samples produced by using different processing methods or technologies in experiment 3 is presented in Table 3. For the first 3 samples produced under laboratory conditions, the CP was increased by both the 3D and QGQF methods. These increases were probably due to reductions in the fiber and fat. The higher CP of the QGQF DDGS was possibly due to leaching of soluble proteins during the soaking process; the water-soluble fraction was included in the final DDGS. The DDGS produced by the 3D and QGQF processes had lower concentrations of fat than did the conventional DDGS. The lower fat content was due to the removal of germ. Total dietary fiber was reduced from 36% in the conventional DDGS sample to 28 and 25% by the 3D and QGQF methods. Most of this reduction was for insoluble fiber, which is the predominant type of fiber in DDGS. The QGQF method yielded lower total and insoluble fiber levels but the highest soluble fiber level. The latter result

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DISTILLERS DRIED GRAINS WITH SOLUBLES AND PROCESSING TECHNIQUES Table 1. Nutrient composition, amino acid contents, and amino acid digestibility coefficients (DC) for distillers dried grains with solubles (DDGS) and its components of wet grains and solubles, experiment 11 Component

DDGS

Grains

Solubles

DM (%) CP (%) Crude fat (%) Ash (%) Phosphorus (%)

87.1 22.33 9.75 4.60 0.72

87.2 27.11 6.98 2.00 0.39

87.8 18.70 12.07 8.70 1.24

Amino acid (%) Asp Thr Ser Glu Pro Ala Cys Val Met Ile Leu Tyr Phe His Lys Arg Trp Mean

Total

DC2 (%)

Total

DC (%)

Total

DC (%)

SEM

1.4 0.9 1.1 3.2 1.8 1.7 0.5 1.1 0.5 0.8 2.8 0.9 1.2 0.6 0.5 0.9 0.2

64b 66b 78b 77b 84b 79b 68b 70b 81b 74c 85b 92ab 85b 74b 38b 78b 85b 75

1.7 1.1 1.3 4.8 2.4 2.2 0.7 1.5 0.6 1.1 3.9 1.1 1.5 0.8 0.8 1.1 0.3

83a 79a 90a 90a 93a 91a 85a 85a 93a 89a 92a 99a 94a 86a 78a 88a 92a 89

1.3 0.8 0.8 2.3 1.3 1.3 0.4 1.1 0.4 0.7 1.8 0.6 0.8 0.6 0.8 0.9 0.2

69b 77a 80b 77b 91a 78b 80a 76b 79b 81b 84b 89b 83b 82a 73a 87a 69c 80

2.2 2.4 2.4 2.0 2.1 1.8 2.6 2.2 2.0 2.1 1.8 3.1 2.0 2.1 2.6 2.2 2.1

Digestibility coefficients within a row with no common superscript are different (P < 0.05). Values for all components are expressed on an as-fed basis. 2 Digestibility coefficients are the mean of 4 cecectomized roosters. a–c 1

suggests that soaking for 12 h resulted in the breakdown or solubilization of some of the insoluble fiber fraction. For total P in the DDGS samples, the P content of the conventional DDGS was similar to that reported by the NRC (1994). Interestingly, the P content of DDGS was reduced by the 3D process but was increased by the

QGQF process. A reduction for 3D was expected because much of the germ was removed and almost 90% of the phytic acid is present in the germ of corn (Ravindran et al., 1995; Rebollar and Mateos, 1999). The increase in P for the QGQF was unexpected and may have been due to leaching of P during the 12-h soaking process. The

Table 2. Effect of autoclaving on amino acid contents (%) and amino acid digestibility coefficients (DC) for distillers dried grains with solubles (DDGS) samples containing different proportions of wet grains and solubles, experiment 2 62:381 Amino acid Asp Thr Ser Pro Ala Cys Val Met Ile Leu Tyr Phe His Lys Arg Trp Mean

Control Total 1.5 1.0 1.1 1.9 1.9 0.5 1.3 0.5 1.0 3.2 0.9 1.2 0.7 0.9 1.1 0.2

2

67:33 Autoclaved

3

DC (%) ab

81 85ab 88abc 92ab 88bc 88a 85ab 90ab 89ab 91abc 94ab 91ab 85ab 78a 91ab 81a 87

Total 1.4 0.9 1.1 1.8 1.8 0.5 1.2 0.5 0.9 3.1 0.8 1.2 0.6 0.6 1.0 0.1

2

DC (%) c

70 74c 81d 86c 84d 81b 78c 84c 83c 88d 89c 86c 78c 64b 86c 65b 80

Control Total 1.5 1.0 1.1 2.0 1.9 0.5 1.3 0.5 1.0 3.3 0.9 1.3 0.7 0.9 1.1 0.2

72:28 Autoclaved

DC (%) a

85 89a 91a 94a 91a 91a 89a 92a 92a 93a 98a 93a 87a 83a 94a 85a 90

Total 1.5 0.9 1.1 1.9 1.9 0.5 1.3 0.5 1.0 3.2 0.9 1.2 0.7 0.6 1.0 0.1

DC (%) bc

75 80bc 84bcd 89bc 87cd 86ab 82bc 87bc 85bc 91bcd 93abc 88bc 82bc 64b 88bc 63b 83

Control Total

DC (%)

1.6 1.0 1.2 2.0 2.0 0.6 1.3 0.5 1.0 3.4 0.9 1.3 0.7 0.9 1.1 0.2

Digestiblity coefficients within a row with no common superscript are different (P < 0.05). Values are the proportions of wet grains vs. solubles on a DM basis. 2 Control = original conventional DDGS; autoclaved = the original DDGS autoclaved for 45 min at 120°C. 3 Values are DC determined in 5 cecectomized roosters each. a–d 1

Autoclaved

a

82 85ab 90ab 93a 90ab 91a 87ab 89ab 90a 93ab 95a 92a 87a 79a 92ab 81a 88

Total 1.5 1.0 1.1 2.0 1.9 0.6 1.3 0.5 1.0 3.4 0.9 1.3 0.7 0.7 1.0 0.1

DC (%) c

73 77c 84cd 87c 85cd 79b 80c 85c 82c 89cd 87bc 87c 78c 62b 85c 64b 80

SEM 2.0 2.3 2.1 1.3 1.0 2.1 1.6 1.1 1.4 0.8 1.8 1.2 1.3 2.5 1.7 2.1

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MARTINEZ-AMEZCUA ET AL. Table 3. Composition of distillers dried grains with solubles (DDGS) samples produced by different processing methods, experiment 3

1

Component (%) DM CP Crude fat Ash Total dietary fiber Insoluble dietary fiber Soluble dietary fiber Total P

Conventional process in laboratory

Dry degerm defiber

Quick germ, quick fiber

Commercial DDGS

Elusieve pan DDGS

91 21.2 13.9 4.3 36.4 34.9 1.5 0.78

87 23.8 8.7 3.1 28.0 26.5 1.5 0.47

78 28.0 5.4 ND2 25.3 22.5 2.8 1.12

89 31.3 11.8 5.3 34.5 33.2 1.3 0.74

91 40.8 15.0 ND 19.7 18.2 1.5 0.90

1

All the components are expressed on a DM basis. ND = not determined.

2

QGQF procedure includes an initial 12-h soaking of the corn in water. The material or nutrients that are soluble in the water are added back to the DDGS in later stages of processing. Thus, any P that was water soluble or that leached into the water was included in the final DDGS. Comparing the commercial DDGS with the Elusieve DDGS, the differences in nutrient composition were generally as expected (Table 3). Elusieve processing greatly reduced the total dietary fiber content, and the levels of CP, fat, ash, and P subsequently increased. In comparing the conventional, 3D, and QGQF DDGS samples for total amino acid concentrations and digestibility coefficients (Table 4), the concentrations of amino acids were generally higher for the 3D and QGQF samples. This increase was expected because the protein content of these samples was higher. A notable exception was the amino acid Lys. The concentration of Lys was lower in the 3D than in the conventional DDGS. As dis-

cussed above, this reduction was probably due to removal of the germ during the 3D process. In addition, the Lys in the QGQF DDGS was not decreased and actually increased, possibly because of the increased protein and leaching of water-soluble protein high in Lys into the water fraction during the soaking process, as discussed for P earlier. When comparing the Lys levels further among the 3 samples on a per-unit of CP basis, the Lys as a percentage of CP in the conventional, 3D, and QGQF DDGS were calculated to be 3.8, 3.0, and 4.2, respectively. The lower level of Lys in the 3D, compared with the other 2 DDGS, was probably due to removal of the germ during the 3D process, as mentioned above. The observation that the Lys, as a percentage of CP, increased and was not also reduced by the QGQF process, in which germ was also removed, was again possibly due to the leaching of water-soluble proteins high in Lys during the 12-h soaking process, as discussed above. Digestibilities of amino

Table 4. Total concentrations and digestibility coefficients (DC) for amino acids in distillers dried grains with solubles (DDGS) samples produced by different processing methods, experiment 3 Conventional (laboratory) Amino acid (%) Asp Thr Ser Glu Pro Gly Ala Cys Val Met Ile Leu Tyr Phe His Lys Arg Trp Mean

Total 1.36 0.86 0.86 2.23 1.08 0.92 1.36 0.42 1.12 0.47 0.81 2.03 0.80 0.93 0.54 0.80 1.05 0.22

1

2

Dry degerm defiber

Quick germ, quick fiber

Commercial

Elusieve pan DDGS

DC (%)

Total

DC (%)

Total

DC (%)

Total

DC (%)

Total

DC (%)

78 77 82 84 88 — 84 76 83 87 84 90 89 88 79 65b 87 93 83

1.57 1.06 1.16 2.78 1.57 0.98 1.74 0.53 1.33 0.62 1.03 2.99 1.14 1.23 0.66 0.72 1.13 0.24

80 80 84 85 91 — 88 81 86 89 86 94 93 91 82 66b 90 92 86

1.79 1.20 1.17 2.35 1.50 1.08 1.64 0.58 1.46 0.54 1.19 2.67 1.08 1.21 0.63 1.17 1.10 0.28

81 78 81 82 90 — 86 77 87 86 88 93 92 92 82 83a 90 93 86

2.02 1.25 1.36 3.80 1.98 1.24 2.17 0.56 1.73 0.61 1.31 3.71 1.31 1.58 0.83 1.12 1.47 0.26

77 83 83 83 90 — 85 81 84 88 86 88 91 89 85 77a 90 94 86

2.60 1.57 1.70 5.05 2.68 1.55 2.79 0.73 2.25 0.77 1.74 4.86 1.79 2.08 1.08 1.35 1.93 0.31

75 82 83 83 88 — 86 78 85 88 87 88 92 90 84 77a 91 94 85

a,b Digestibility coefficients within a row with no common superscripts are different (P < 0.05). A significant difference was observed only for Lys. 1 Amino acid concentrations are on a DM basis. 2 Digestibility coefficients determined in 5 cecectomized roosters.

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Table 5. Fatty acid profile of a sample of corn, commercial distillers dried grains with solubles (DDGS), and DDGS produced by using the conventional dry-grind method under laboratory conditions (as-is basis) Corn

Commercial DDGS

Conventional DDGS2

Fatty acid1

Structure

%3

mg/g4

%

mg/g

%

mg/g

Lauric Tridecanoic Myristic Pentadecanoic Palmitic Palmitoleic Heptadecanoic Stearic Oleic Linoleic Arachidic Linolenic Cis-11-eicosenoic Cis-11,14-eicosadienoic Cis-8,11,14-eicosatrienoic Cis-4,7,10,13,16,19-docosahexaenoic

12:0 13:0 14:0 15:0 16:0 16:1 17:0 18:0 18:1n-9 cis 18:2n-6 cis 20:0 18:3n-3 20:1 20:2 20:3n-6 22:6n-3

0.234 1.441 0.000 0.000 13.529 0.099 0.000 1.655 22.916 59.036 0.332 1.671 0.247 0.000 0.147 0.000

0.085 0.522 0.000 0.000 4.904 0.036 0.000 0.600 8.307 20.312 0.120 0.606 0.089 0.000 0.053 0.000

0.036 0.133 0.086 0.000 12.772 0.117 0.083 2.033 23.173 56.259 0.388 1.477 0.266 0.051 0.160 0.089

0.038 0.140 0.091 0.000 13.524 0.124 0.087 2.152 24.538 59.572 0.411 1.564 0.281 0.054 0.170 0.094

0.050 0.045 0.183 0.013 14.353 0.820 0.095 2.504 24.394 50.359 0.415 1.629 0.260 0.048 0.179 0.135

0.053 0.048 0.193 0.014 15.117 0.863 0.100 2.637 25.692 53.038 0.437 1.716 0.274 0.051 0.189 0.142

1

No measurable conjugated linoleic acid was found in any of the samples. Distillers dried grains with solubles produced under laboratory conditions by using conventional processing. 3 Expressed as g/100 g of fatty acid. 4 Expressed as mg/g of sample. 2

acids for the conventional, 3D, and QGQF DDGS were similar, with the exception of Lys, for which the QGQF DDGS had higher (P < 0.05) Lys digestibility. When comparing the commercial DDGS and the Elusieve DDGS (Table 4), as expected, concentrations of all amino acids were substantially higher in the Elusieve DDGS because of its increased protein and decreased fiber. Digestibilities of amino acids in the 2 samples were similar, indicating that protein associated with the fiber fraction of the DDGS was digested similarly to that in the nonfiber fraction. In general, no large changes in fatty acid profile (%) were observed among corn and the 2 DDGS samples, conventional laboratory DDGS, and commercial DDGS (Table 5). Only a small reduction in linoleic acid and minor increases in stearic and oleic acids were observed among the corn and the DDGS samples. These results agree with those reported by Dawson et al. (1987) and O’Palka et al. (1987), who observed reductions in unsaturated fatty acids and increases in more saturated fatty acids for DDGS relative to corn, but those effects were due to nonspecific hydrolysis caused by unsanitary conditions or the equipment used to ferment the grains. Before fermentation in commercial conditions, the corn is mixed with the mash during cooking preconditioning and is heated to 90°C to minimize microbial populations (Kelsall and Lyons, 2003). This step was not included in the production of the laboratory conventional DDGS in our study, which may explain the small differences in stearic, oleic, and linoleic acids between the 2 DDGS samples. In general, the fatty acid concentration differences between corn and DDGS are in agreement with the general rate of increase of 3:1 in DDGS:corn attributable to fermentation and removal of most of the starch. No CLA was found in the 2 DDGS samples (data not shown). Thus, the fermentation process involved in etha-

nol production did not promote transformation of linoleic acid to CLA, even though fermentation to produce ethanol includes anaerobic and reducing conditions, which are important characteristics in the production of CLA in the rumen of ruminant animals. As stated by Kamlage et al. (1999), very little is known about CLA production; however, it seems to be mainly associated with the bacterial population. The current study indicates that Saccharomyces cerevisiae, at least under fermentation conditions, does not have the ability or preference to conjugate linoleic acid to CLA. We also observed that corn is not a significant source of 22:6n-3 (docosahexaenoic acid), but DDGS samples produced under conventional conditions do contain small amounts. The latter may be provided by the yeast, which has the potential to modify the fatty acid profile, depending on the fermentation conditions, particularly where temperature plays a major role (Torija et al., 2003). The results of this study indicate that the processing method or technology can greatly influence the nutritional composition and value of DDGS. Varying the amount of solubles in DDGS and using new or modified processing technologies to remove fiber, germ, or both can influence the protein-amino acid and P content of DDGS but generally did not have a substantial effect on the digestibility of amino acids. Previous studies (Belyea et al., 1998; Spiehs et al., 2002; Belyea et al., 2004) have reported that the nutrient composition of DDGS produced under normal commercial conditions can vary substantially, presumably mainly because of variation in the degree of starch fermentation and ethanol yield, and also drying conditions. The results of the current study indicate that new processing technologies to remove fiber and germ will result in even greater variation in the nutritional composition and value of DDGS.

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