CASE STUDY: Distiller’s Dried Grains With Solubles Affects Fatty Acid Composition of Beef

By Lancaster, P A Corners, J B; Thompson, L N; Fritsche, K L; Williams, J E

ABSTRACT Sixteen steers (BW = 394.7 +- 20.7 kg) were allotted by weight to 1 of 2 treatments to test the effects of distiller’s dried grains with solubles (DDGS) on the fatty acid profile of muscle tissue. Treatments consisted of a whole shelled corn, soybean hulls, and alfalfa hay based finishing diet with DDGS included at 16% of DM or soybean meal and cracked com (control), which were fed for approximately 77 d. Diets were formulated to be isocaloric at 1.44 and 1.45 Mcal of NEg/kg of DM for DDGS and control treatments, respectively. At slaughter, a 2.5 cm thick cross section of the LM was taken between the 11th and 12th rib; all external fat around the cut was removed, and the cut was stored at -80[degrees]C for later analysis. The chemical composition of LM (i.e., moisture, crude fat, CP, and ash) did not differ (P > 0.10) between treatments. Fat tissue extracted from LM samples was separated into triacylglycerol and phospholipid fractions and analyzed for fatty acid composition. There was no effect of treatment on the fatty acid composition of the triacylglycerol fraction. However, in the phospholipid fraction, DDGS increased (P < 0.05) linoleate (18:2n6 cis; 29.3 vs. 20.7%, respectively) and PUFA (43.7 vs. 32.5%, respectively) in LM samples compared with control. In conclusion, DDGS increased the amount of unsaturated fatty acids in the phospholipid but not the triacylglycerol fraction of LM.

Key words: distiller’s dried grains with solubles, fatty acid composition, muscle

INTRODUCTION

Beef has been criticized for a greater concentration of saturated fatty acids (SFA) compared with PUFA; thus, an unhealthy choice for today’s society (Wood et al., 1999). Conversely, increasing the PUFA content of beef is difficult due to hydrogenation by rumen microbes, which are sensitive to unsaturated fatty acids (Jenkins, 1993). However, if PUFA are protected against microbial attack, they can pass to the small intestine and be absorbed. Studies have shown that encapsulation of oils with formaldehyde-treated casein protects PUFA from microbial biohydrogenation (Scott et al., 1971; Cuitun et al., 1975). In addition, Scott et al. (1971) reported that feeding protected safflower oil to sheep increased linoleate (18:2n6 cis) in perirenal and subcutaneous fat depots. Others observed greater linoleate in semimembranosus and LM muscles of lambs fed protected cottonseed oil (Mata-Hernandez et al., 1978).

In the past, creating protected oils was most likely not economical due to a lack of premiums for healthier beef. Today, however, one abundant feedstuff may provide protected oil economically. Distiller’s dried grains with solubles (DDGS) is a coproduct of ethanol production from corn, which has a significant amount of linoleate (30 to 60% of total fatty acid; Harfoot, 1981), but less oil content (4% DM; NRC, 1996). The oil content of DDGS (11%) is approximately 3 times that of corn (NRC, 1996). During the liquefaction process, the mash is heated causing zein proteins of the corn kernel to denature. Zein proteins are hydrophobic molecules that associate with membranes and readily self-aggregate when exposed to aqueous environments (Argos et al., 1982). These properties may cause them to associate with other hydrophobic molecules (i.e., triglycerides) during the ethanol process. Zein proteins comprise 40% of corn protein (Argos et al., 1982) and are resistant (16.2% degradable) to microbial degradation (Romagnolo et al., 1994). Encapsulation of PUFA by a protein resistant to microbial degradation may protect them from biohydrogenation even without formaldehyde treatment. Despite this, no studies have evaluated the effect of DDGS on the fatty acid profile presented to the small intestine or on the composition of beef. Based upon this, the objective of this study was to test the hypothesis that DDGS will increase the unsaturated fatty acid composition of beef.

MATERIALS AND METHODS

Animals and Management

Sixteen yearling steers (initial BW = 394.7 +- 20.7 kg) were allotted by BW to 2 dietary treatments (8 steers per pen). Treatments included a mixture of whole shelled and steam flaked corn, soybean hulls, and alfalfa haybased finishing diet with DDGS, or soybean meal (SBM) and cracked corn (control). Distiller’s dried grains with solubles were included at 16% of diet DM as a protein and energy source replacing a portion of the corn and SBM in the control diet according to Gordon et al. (2002a) who reported that inclusion of DDGS in finishing diets at 15% provided optimal performance. Steers were adapted to the high grain diet over a 24-d period before treatments began. The percentage of corn in the diet was increased again 14 d later resulting in the final diet (Table 1). The inventory of steam flaked corn was not sufficient to last the entire feeding period and was gradually replaced by whole shelled corn over a 15-d period midway through the trial.

The basal diet (corn, soybean hulls, and alfalfa hay) was mixed and fed once daily. Supplements were mixed in bulk ahead of time and top-dressed immediately after delivery of the basal diet at 1.65 and 1.66 kg of DM/hd per day for the control and DDGS treatments, respectively. Steers were fed to maintain similar intakes between treatment groups ensuring that the change in fatty acid profile was due to DDGS rather than different fatty acid intake from the basal diet. Steers were slaughtered in 2 groups of similar fat thickness based on ultrasound measurements. The first group, which was slaughtered after 73 d on treatment, consisted of the 4 steers from each treatment with the greatest fat thickness. The second group, consisting of the remaining 4 steers on each treatment, was slaughtered after 80 d on treatment.

Table 1. Composition of experimental diets fed to steers

Sample Collection and Analysis

Immediately after the carcass was split, a 2.5 cm thick cross section of the facial LM was taken from the right side of the carcass. Muscle tissue was dissected of intermuscular and subcutaneous fatty tissue and placed in freezer bags. Muscle samples were placed in a cooler at 2[degrees]C until all muscle samples from that slaughter group were collected. Muscle samples were then frozen at -80[degrees]C for later analysis. Within 6 mo of collection, muscle samples were thawed and ground using a food processor until thoroughly ground and mixed. Ground tissue was subsampled (1 g) in triplicate and placed into 50 mL polypropylene centrifuge tubes. Ten mL of 50 mM Trizma HC1 (pH 7.4) and 1 mM EDTA-disodium salt mixture was added to polypropylene tubes. Samples were homogenized for 30 s with a Tissue Tearor (model 985-370; Biospec Products Inc.-Dremel, Racine, WI) while tubes were on ice.

Total lipids were extracted from aliquots of the homogenate using chloroform and methanol (2:1 vol/vol) following the addition of internal standards (i.e., trinonadecanoin and 1,2-heptadecanoic phosphatidylcholine) according to the modified Folch procedure (Bligh and Dyer, 1959). Lipid extracts were separated into triacylglycerol and phospholipid fractions by thin layer chromatography using a solvent system of hexane, diethyl ether, and glacial acetic acid (80:20:2, vol/vol/vol). Lipids were separated due to previous research indicating that linoleate is preferentially incorporated into phospholipids (Noble, 1981). These lipid fractions were prepared for fatty acid analysis by basic methylation using 0.5 N sodium methoxide according to the manufacturer’s instructions (Supelco, Bellefonte, PA). Fatty acid methyl esters were analyzed by GLC (Varian Model 3400; Varian Associates, Walnut Creek, CA) using a fused-silica capillary column (100 m x 0.25 mm i.d., 0.20 [mu]m film thickness; Supelco SP-2560). The GLC conditions were as follows: injector, 220[degrees]C; detector, 250[degrees]C; initial oven temperature, 160[degrees]C for 2 min, then increased 3[degrees]C/ min to 220[degrees]C; held at 220[degrees]C for 30 min for a total run time of 52 min. Peaks were identified by comparing retention times with those of corresponding standards (i.e., PUFA II and FAME-37; Supelco).

Ground muscle tissue samples were subsampled in duplicate and subjected to DM determination (AOAC, 1995). An additional subsample of muscle tissue was lyophilized, ground using a mortar and pestle, and analyzed for DM (AOAC, 1995), OM (AOAC, 1995), N content by combustion analysis (LECO Instrument Inc., St. Joseph, MI; AOAC, 1995), and crude fat extraction (AOAC, 1995).

Samples of basal diet ingredients were taken weekly and composited biweekly for analysis. Samples of the supplement ingredients (i.e., DDGS, SBM, and cracked corn) were taken prior to mixing the supplements. Composite samples of the basal diet and supplement ingredients were ground (Wiley Mill, Thomas Scientific, Swedensboro, NJ) to pass through a 2-mm screen and analyzed for DM (AOAC, 1995), N content by combustion analysis (AOAC, 1995), and NDF (Van Soest et al., 1991).

A composite of each dietary ingredient was made on an equal weight basis and duplicate subsamples analyzed for fatty acid composition using a one-step methylation procedure with benzene as the solvent (Sukhija and Palmquist, 1988). A sample sufficient to yield approximately 50 mg of fatty acids was selected based on previous ether extraction. Trinonadecanoin was added (0.5 mL of a 4 mg/ml solution) as an internal standard. Lipids were prepared for fatty acid analysis by acid methylation with 5% methanolic hydrochloride. Samples were incubated in a 70[degrees]C water bath for 16 h to increase efficiency of methylation according to Jenkins et al. (2001). Methyl esters were analyzed by GLC (Varian Model 3400; Varian Associates) using a fused-silica capillary column (30 m x 0.25 mm i.d., 0.20 [mu]m film thickness; Supelco SP-2380). The GLC conditions were as follows: injector, 250[degrees]C; detector, 270[degrees]C; initial oven temperature, 70[degrees]C for 2 min, then increased 4[degrees]C/min to 220[degrees]C; held at 220[degrees]C for 1 min, then increased 10[degrees]C/min to 250[degrees]C for 5 min for a total run time of 48.5 min. Peaks were identified as described previously using a FAME-37 standard (Supelco, Bellefonte, PA). In Situ Rumen Incubation

Two Angus crossbred steers (average BW = 613.6 +- 19.3 kg) with ruminal cannulas were used to determine the in situ rumen escape of linoleic acid of DDGS. A clinical veterinarian performed surgical procedures at the University of Missouri College of Veterinary Medicine Large Animal Clinic approximately 18 mo prior to this study. The University of Missouri Animal Care and Use Committee approved all procedures and surgical justifications. Cannulated steers were fed once daily a high concentrate base diet (80% whole shell corn, 15%) soybean hulls, and 5% fescue hay on an as-fed basis) top-dressed with 1.66 kg of DM/hd per day of the supplement fed to the DDGS treatment during the study. A sample of DDGS was ground (Wiley Mill, Thomas Scientific) to pass through a 2-mm screen. Approximately 6 g (as-fed basis) were weighed into prelabeled Dacron bags (10 x 20 cm, 53 +- 10 [mu]m pore size; Ankom, Fairport, NY). Dacron bags were heat-sealed (1.3 cm from the open end) and fastened to a short section of heavy chain using nylon cable ties. Duplicate bags were incubated for 0, 6, 12, 24, 48, and 72 h in the rumen of each steer. All bags were inserted into the rumen approximately 2 h after feeding and removed at the appropriate time points. Upon removal from the rumen, bags were rinsed with cold tap water and stored at 5[degrees]C until all bags were removed, at which time they were stored at -18[degrees]C for later analysis. Bags were thawed in tepid water, thoroughly rinsed under warm tap water until water ran clear from the bag, dried at 105[degrees]C overnight, and weighed for calculation of DM residue remaining. The residue in each bag at each time point was subjected to fatty acid analysis as previously described for diet ingredients.

Fatty acid analysis of in situ residues was used to calculate that proportion of linoleic acid escaping biohydrogenation, termed rumen escape linoleic acid (RELA). The procedure used to calculate RELA has been described previously for N degradation (Lancaster et al., 2007). The rate of hydrogenation was determined experimentally as 6.30%/h, and the NRC (1996) was used to determine the solid and liquid dilution rates of 3.73%/h and 8.00%/h, respectively, for the diet fed.

Statistical Analysis

Data were analyzed as a completely randomized design using the GLM procedure of SAS (SAS Inst. Inc., Cary, NC). Muscle tissue was subsampled, and thus treatment and steer within treatment were included in the model, using steer within treatment to test treatment means. Animal was the experimental unit.

Table 2. Chemical composition of distiller’s dried grain with solubles fed to steers

Only individual fatty acids that comprised a significant proportion (> 1%) of the total fatty acids are presented; however, total fatty acids, PUFA, SFA, and monounsaturated fatty acids (MUFA) values include all fatty acids analyzed.

RESULTS AND DISCUSSION

The chemical composition of the DDGS used in the study is presented in Table 2. The DDGS was similar to NRC (1996) reported values for CP and fat, but had greater amounts of NDF. The total fatty acids extracted from DDGS by the Sukhija and Palmquist (1988) onr-step method is considerably greater than the crude fat measurements using diethyl ether. The reason for this is unknown. Sukhija and Palmquist (1988) reported that the fat content determined by petroleum ether extraction was greater than that for the one-step method for most feed samples, but for one sample the fat content determined by the one-step method was greater than that for the petroleum ether extraction.

The fatty acid composition consisted primarily of linoleate (18:2n6 cis; 55%), oleate (18:1n9 cis; 28%) and palmitate (16:0; 12%). Thus, inclusion of DDGS in the finishing diet increased the linoleate, oleate, and palmitate concentrations in the DDGS diet (Table 1). However, this effect was mainly due to a greater amount of total fatty acids in DDGS compared with the control diet (76.8 vs. 54.3 mg/g DM, respectively). This does not negate the fact that the oil in DDGS is protected from biohydrogenation in the rumen. Previous studies have reported no significant increase in unsaturated fatty acid composition of tissues when oils were fed unless the oil was protected in some manner (Mata-Hernandez et al., 1978; Ponnampalam et al, 2001a).

Only 11.1% of the linoleate contained in DDGS remained in the residue at 0 h, thus 88.9% of the linoleate was associated with feed particles washed from the Dacron bag (data not shown). This is reasonable if the linoleate is encapsulated in zein proteins that are denatured, exposing the hydrophilic amino acid residues resulting in hydrophilic protein aggregates. Feed particles associated with the liquid phase have a faster passage rate from the rumen than particles associated with the particulate phase. In addition, a smaller proportion of the bacterial population is associated with the liquid than particulate phase (25 vs. 75%, respectively; Brock et al., 1982); thus, degradation of these feed particles and subsequent biohydrogenation of the PUFA may be slower or less extensive. However, Mahadevan et al. (1980) found that soluble and insoluble protein fractions of SBM were degraded at similar rates. Therefore, greater passage rate of the soluble fraction, with which the majority of linoleate was associated, may contribute to the limited biohydrogenation of linoleate. It is not known whether any relationship exists between the rumen escape of linoleic acid and the protein in DDGS; however, the similarity in the RELA (55% of linoleic acid) and the RUP (52% of CP; NRC, 1996) for DDGS is noteworthy. More research is warranted to evaluate this relationship in the degradability of these components in the rumen.

Treatments were similar (P > 0.10) in the chemical composition of the fresh longissimus dorsi cross sections (Table 3). Therefore, differences observed in fatty acid composition are due to changes in fatty acid profile, not differences in the amount of fat in tissue samples. The chemical composition in this study is similar to that of Brackebusch et al. (1991) and French et al. (2000) who reported values for LM trimmed of intermuscular and subcutaneous fat.

Triacylglycerol Fraction of Muscle Lipids

There was no effect (P > 0.10) of treatment on the fatty acid composition of the triacylglycerol fraction of longissimus dorsi tissue (Table 4). Palmitate, oleate, and stearate comprised the majority of the fatty acids present for both DDGS and control steers (87.6 and 87.4%, respectively), which agrees with the data of Ponnampalam et al. (2001b) who fed protected sunflower meal to lambs. Even though not significant (P > 0.10), inclusion of DDGS in the finishing diet numerically reduced the amount of SFA and increased the amount of MUFA and PUFA compared with the control treatment. The lack of a difference may be attributed to the time cattle were fed the DDGS and control diets. Rule et al. (1997) found that yearling steers required 90 d on feed to change the amount of MUFA significantly in total lipids of longissimus tissue after a switch from forage to a concentrate-based diet, whereas SFA did not change within 135 d on feed. Duckett et al. (1993) found that 84 and 168 d on feed were required to significantly change the amounts of MUFA and SFA in the neutral lipid fraction of longissimus tissue, respectively.

Table 3. Chemical composition of fresh cross section of LM from steers

Phospholipid Fraction of Muscle Lipids

The fatty acid composition of the phospholipid fraction of longissimus tissue was affected to a greater extent than the triacylglycerol fraction by the inclusion of DDGS in the diet. Linoleate was increased (P < 0.05) 40% by the inclusion of DDGS in the diet compared with control. Bolte et al. (2002) found a similar magnitude of change in linoleate in the longissimus dorsi and semitendinosus muscle of lambs fed high-linoleate safflower seeds. Felton and Kerley (2004) found a slightly greater magnitude of change (53%) in linoleate amounts in LM of steers fed whole, raw soybeans high in linoleate (52% of total fatty acids). The levels of linoleate in tissue lipids are greater in this study than those of Bolte et al. (2002) and Felton and Kerley (2004); however, these authors did not separate lipids into triacylglycerol and phospholipid fractions. Amounts of PUFA were greater (P < 0.05) for DDGS steers compared with control steers, which was primarily due to the increase in linoleate. The amounts of SFA and MUFA were not affected by dietary treatments, which agrees with the results of Felton and Kerley (2004).

Table 4. Fatty acid composition of a cross section of LM from steers

The PUFA:SFA ratio is an important nutritional index for healthiness of meat products consumed by humans, for which the recommended ratio is 0.45 or above (Wood et al., 1999). There was no effect of treatment on the PUFA:SFA ratio in the triacylglycerol fraction. However, in the phospholipid fraction, there was a trend (P < 0.10) for DDGS steers to have a greater PUFA:SFA ratio than control steers (1.23 vs. 0.93, respectively). Both are above the recommended level, but DDGS improved the ratio. These values are similar to those reported by Marmer et al. (1984) for the neutral (0.1) and polar (1.1) lipid fractions of LM. Increasing the PUFA level of beef increases the potential for oxidation, reducing shelf life and retail-display appeal to consumers. Previous research by Gordon et al. (2002b) has evaluated retail-display attributes and consumer acceptance of beef when DDGS was included in the diet (0, 15, 30, 45, 60, and 75% of diet DM). Results indicated that there was no effect on lightness, or red and yellow color. However, after 7 d in a retail display the hue angle (relationship of yellow to red coloration) tended to increase linearly with greater dietary inclusion rate of DDGS. A sensory panel evaluation indicated the perception of myofibrillar and overall tenderness increased and connective tissue decreased with increasing DDGS in the diet. However, there was a numerical trend for flavor and off-flavor intensity to increase with increasing DDGS, suggesting that greater inclusion rate of DDGS may adversely affect consumer acceptance of beef, which may be attributed to the level of PUFA.

IMPLICATIONS

Given the increasing demand for biofuels to replace petroleum, DDGS will most likely become an increasing feed source for beef cattle. Our study provides evidence that inclusion of DDGS at just 15% of diet DM can significantly improve the perception of beef as a healthy consumer choice. However, further research needs to evaluate these effects in larger groups of cattle, in addition to evaluating the wet vs. dry form of distiller’s grains because substantial amounts are fed in the wet form. Further research is also wananted in assessing the impact of consumption of beef from cattle fed DDGS on human health.

ACKNOWLEDGMENTS

The authors gratefully acknowledge Eric Berg and his lab and Jim Porter for their assistance in this project. The authors greatly appreciate the partial support from Broins and Associates, Sioux Falls, SD and NEMO Grains LLC, Macon, MO for this research project.

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P. A. Lancaster, J. B. Corners, L. N. Thompson, K. L. Fritsche, and J. E. Williams,1 PAS

Department of Animal Sciences, University of Missouri, Columbia 65211

1 Corresponding author: Williamsje@ missouri.edu

Copyright American Registry of Professional Animal Scientists Dec 2007

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