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Meat quality responses to feeding distiller’s grains to finishing Holstein steers^1,2

Department of Animal Sciences, University of Minnesota, St. Paul 55108-6111

	Abstract

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Strip loins from two experiments were used to evaluate effects of feeding dry (DDG) or wet (WDG) distiller’s grains on beef color, tenderness, and sensory traits of Holstein steers. In Exp. 1, conducted at the University of Illinois at Champaign–Urbana, dietary treatments consisted of a control whole corn–corn silage diet with soybean meal (SBM) or diets formulated with 12.5% DDG plus urea, 25% DDG, 25% WDG, 50% DDG, or 50% WDG (DM basis). In Exp. 2, conducted at Iowa State University, dietary treatments consisted of cracked corn–corn silage–hay diets with either SBM or urea (Urea) as the control diets, or diets formulated with 10, 20, or 40% DDG or WDG (DM basis). Within each study, strip loins from each of four steers (representing 45.7 and 66.6% of steers in Exp. 1 and 2, respectively) in four replicate pens per treatment were aged for 13 d at 4°C for subsequent color, tenderness, and palatability evaluation. Color of steaks was measured objectively using a HunterLab Miniscan XE spectrophotometer and was subjectively evaluated by a trained panel. Tenderness was measured using the Warner-Bratzler shear force (WBSF) instrument on steaks cooked to 70°C. For sensory evaluation, 95 consumers were recruited to evaluate tenderness, juiciness, and flavor of cooked steaks. In Exp. 1, steaks from steers fed 25% WDG had higher (P < 0.05) a* values after 138 h of simulated retail display than all other treatments, except for those from steers fed 12.5% DDG. In Exp. 2, a greater (P < 0.05) percentage of steaks from steers fed 40% DDG or 40% WDG were considered moderately undesirable during retail display (steaks that received a consumer acceptability score of 3 or less). There were no (P = 0.20 in Exp. 1, and P = 0.33 in Exp. 2) differences among treatments in Exp. 1 and Exp. 2 for WBSF (1.47 ± 0.66 kg and 1.58 ± 0.72 kg, respectively) or taste panel tenderness (5.7 ± 0.30 and 6.2 ± 0.22, respectively), beef flavor (6.0 ± 0.23 and 6.2 ± 0.22, respectively), and juiciness (5.6 ± 0.31 and 5.8 ± 0.23). Feeding distiller’s grains at up to 50% of the dietary DM did not affect tenderness or sensory traits, and seems to be a viable feed alternative without negatively impacting sensory attributes.

Key Words: Beef • Carcass • Distiller’s Grains • Holstein • Sensory Traits

	Introduction

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The prevalence of distiller’s grains (DG) from dry milling of corn is increasing in the upper Midwest due to growing interest in processing corn for ethanol production. Increased production of DG is leading cattle feeders and others in the beef industry to consider DG as a feed source. Ojowi et al. (1997) observed that steers fed a diet consisting of wheat-based DG had more (P < 0.05) intermuscular fat and less (P < 0.05) s.c. fat than those fed wet brewer’s grains or barley. Reports from Canada indicated that steaks from steers fed wheat-based DG were similar in sensory traits and shear force values to those from steers fed brewer’s grains or barley (Shand et al., 1998).

Distiller’s grains have significant concentrations of vitamins, including B complex, A, D, and E; however, it is not known whether these characteristics of DG contribute to enhancing the value of beef. Dahlen et al. (2001) reported that steaks from steers fed a combination of condensed distiller’s solubles (a component of DG with solubles) and barley by-product were redder than steaks from steers fed corn gluten feed. These studies have evaluated beef cattle fed DG, but limited information exists on the effects of DG on beef tenderness and sensory traits.

Because consumer preference for wholesome, high-quality beef is the focal point of the beef industry, it is imperative that we gain knowledge on the effect of feeding DG on beef quality and sensory traits. Therefore, the objective of this study was to determine the effects of feeding dry or wet DG on beef quality traits and sensory attributes from Holstein steers.

	Materials and Methods

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Strip Loin Collection
Carcasses were selected randomly using a random number generator before carcass data collection, and subsequently, fabricated according to North American Meat Processors guidelines (NAMP, 1997). Strip loins (NAMP #180) were collected from carcasses of steers fed DG for 270 and 299 d at University of Illinois at Champaign–Urbana (Exp. 1) and Iowa State University (Exp. 2), respectively. In Exp. 1, Holstein steers were fed a control diet that consisted of whole corn-corn silage diet with soybean meal (SBM), or diets containing 12.5% dry distiller’s grains (DDG) plus urea, 25% DDG, 25% wet distiller’s grains (WDG), 50% DDG, or 50% WDG (Table 1). In Exp. 2, Holstein steers were fed control diets of cracked corn–corn silage–hay diets supplemented with either urea or SBM, or dietary treatments that included 10% DDG, 10% WDG, 20% DDG, 20% WDG, 40% DDG, or 40% WDG (Table 2). Detailed descriptions of treatment allotment and cattle management in Exp. 1 and 2 are reported by Rinker and Berger (2003) and Trenkle (2004), respectively.

Simulated Retail Display
After each steak was over-wrapped with a polyvinyl chloride film, steaks were placed on a table in a cooler maintained at 2 ± 1°C. In accordance with the guidelines of Hunt et al. (1991), steaks were exposed to continuous 807 to 1,614 lx of deluxe warm-white, fluorescent lighting (bulb type = F32T8/TL741; Phillips Inc., Somerset, NJ). Beginning at 6 h under display conditions, each steak was objectively and subjectively evaluated for color attributes at 12-h intervals during retail display for 6 d.

Objective Color Evaluation
The color of each steak was measured with a HunterLab Miniscan spectrophotometer equipped with a 6-mm aperture (Hunter Laboratory Associates, Inc., Reston, VA) and using illuminant D65 to determine CIE (1976) L* (measure of darkness to lightness), a* (measure of redness), and b* (measure of yellowness) values. The mean of three random readings on each steak at the beginning of simulated retail display, after 6 h of display, and at 12-h intervals were used for statistical analyses.

Subjective Color Evaluation
A three-person, trained panel of the University of Minnesota personnel subjectively evaluated color. Panelists were trained using a system of open discussion and the procedure outlined by Lavelle et al. (1995). Panelists assigned scores to each steak for muscle color, overall appearance, and surface discoloration at each evaluation time as prescribed by Hunt et al. (1991). Panelists characterized meat color (8 = extremely bright cherry red, to 1 = extremely dark red), overall appearance (8 = extremely desirable, to 1 = extremely undesirable), and surface discoloration (8 = no [0%] discoloration, to 1 = complete [76 to 100%] discoloration). Steaks were evaluated until at least 80% of the steaks were assigned a mean overall appearance score of 3 (moderately undesirable) or lower.

Tenderness Determination
Steaks were removed from the freezer, thawed for 24 h at 4°C, and then cooked in electric clam shell type grills (model GGR88DK, Salton, Inc., Lake Forest, IL) to a final internal temperature of 70°C. Internal temperature was monitored with a thermocouple (Type T, Omega Engineering, Stamford, CT) inserted into the geometric center of each steak. Each steak was cooled to room temperature, and six to ten 1.27-cm-diameter cores were removed from each steak parallel to the muscle fiber orientation using a hand-coring device. A single, peak shear force measurement was obtained for each core using the WBSF instrument (G-R Elec. Mfg. Co., Manhattan, KS). Peak WBSF values from each steak were averaged for statistical purposes.

Palatability Determination
Ninety-five consumers were recruited from the Minneapolis/St. Paul metropolitan area using the University of Minnesota’s Food Sensory Center’s consumer database. Panelists evaluated tenderness, juiciness, and flavor of cooked steaks, and were given verbal instructions on how to evaluate each sample. Panelists evaluated the palatability attributes of the steaks cooked to 70°C (medium degree of doneness). Steaks were thawed and cooked in the same manner for palatability determination as for the WBSF determinations. When steaks were removed from the grill, 1.27 x 1.27 x 2.54 cm cubes were cut and served to the panelists for evaluation. Each consumer evaluated 14 steak samples in their assigned session, with a break after the seventh sample. Consumers were provided distilled water and unsalted saltine crackers to cleanse their palates between samples. Consumers evaluated samples for like/dislike of tenderness, juiciness, and flavor (1 = dislike extremely, to 9 = like extremely), and were asked whether they were satisfied with the overall eating quality of the steak sample. Demographic information was collected from each consumer during the study.

Statistical Analyses
Data from each experiment were analyzed separately because treatment groups were confounded within study location. Each experiment was analyzed individually, with pen as the experimental unit. Simple descriptive statistics for the carcasses from which strip loins were collected were computed for each treatment group in each experiment. All data were analyzed using the mixed model procedure of SAS (SAS Inst., Inc., Cary, NC), and pairwise t-tests were used to separate least squares means with 0.05. The ANOVA model for simulated retail display included dietary treatment and dietary treatment x duration of simulated retail display as the fixed effects, with duration of simulated retail display as a repeated measure. Additionally, ² analysis was used to ascertain differences between treatments for the percentage of steaks that were "moderately unacceptable" during simulated retail display. The model for WBSF data included dietary treatment as a fixed effect and marbling score as a covariate, whereas the model for consumer taste panel data included dietary treatment as the lone fixed effect and consumer within session as the random effect. Additionally, an orthogonal contrast was used to ascertain a difference in simulated retail display, WBSF, and consumer taste panel data between DDG and WDG in cattle finishing diets.

	Results and Discussion

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Performance and carcass characteristics of steers in Exp. 1 and 2 were presented by Rinker and Berger (2003) and Trenkle (2004), respectively. Strip loins obtained from Exp. 1 and 2 were from carcasses with an average carcass weight of 333 and 364 kg, s.c. fat thickness of 0.57 and 0.70 cm, LM area of 73.7 and 78.9 cm², yield grade of 2.6 and 3.4, and marbling score of Small⁴⁸ and Modest⁰⁵, respectively.

Retail Display
There were no (P = 0.42) duration of simulated retail display x dietary treatment interactions for any color trait. Therefore, only the main effect of dietary treatments on beef appearance, and L*, a*, and b* values at 138 h of simulated retail display (time at which >50% of the steaks evaluated were classified as "moderately unacceptable" by trained panelists) are presented in Table 3.

Although there was no (P = 0.73) effect of diet on L* values in Exp. 1, steaks from steers fed the control diet supplemented with SBM, 20% DDG, 40% DDG, and 40% WDG were lighter (higher L* values; P < 0.05) than steaks from steers fed 10% of either DDG or WDG in Exp. 2 (Table 3). On the other hand, in Exp. 1, steaks from steers fed 12.5 and 25% WDG were more yellow (higher b* values; P < 0.05) than those from steers fed the control diet (with SBM) or 25% DDG; however, b* values were not (P = 0.58) affected by dietary treatment.

Shear Force
To ensure that differences being evaluated were due to dietary treatments, WBSF data were adjusted to a common marbling score. In Exp. 1, marbling score was not significant (P > 0.23) and therefore was removed from the model; however, in Exp. 2, the marbling score covariate was significant (P < 0.05). No differences in WBSF values were observed among treatments (Table 4) in either Exp. 1 (P > 0.20) or Exp. 2 (P > 0.32); however, WBSF values were below the consumer acceptability threshold reported by Shackelford et al. (1991). Results of this study are in agreement with those of Kroger et al. (2004), who failed to find a difference in WBSF values among cattle fed a control finishing diet or diets containing 20 and 40% WDG or DDG.

Consumer panel results for Exp. 1 and 2 are presented in Table 5. Steaks from steers fed 25% WDG received the highest, and those from steers fed 50% WDG the lowest numerical tenderness (P = 0.081) and juiciness (P = 0.083) like/dislike scores; however, flavor like/dislike ratings did not (P = 0.224) differ among dietary treatments in Exp. 1. Across all dietary treatments in Exp. 1, almost half (49%) the consumers were pleased with the overall quality of the samples in the treatment group. Nonetheless, when consumers were displeased with quality of a sample, they were more often dissatisfied with the tenderness of the sample than with the juiciness or the flavor.

Consumer panel results in Exp. 1 and Exp. 2 were similar to those of Shand et al. (1998), who documented that there was no effect of feeding brewer’s grains or wheat-based DG on sensory characteristics of steaks. Given WBSF values obtained in Exp. 1 and 2, high levels of consumer acceptance for tenderness were expected; however, even though consumers tended to "rank" the dietary treatments in accordance to WBSF in both experiments, the percentages of displeased consumers did not differ and these percents were higher than expected given shear force values. The percentage of unpleased consumers that were dissatisfied with tenderness also was surprisingly high, which is perhaps due to some consumers’ generalization of a trait (tenderness, juiciness, flavor) because of an unfavorable evaluation of the flavor or juiciness of the sample (also known as the halo effect and their inability to completely separate tenderness, juiciness, and flavor), similar in principle to the halo effect documented by Roeber et al. (2000).

	Implications

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Results of this study indicate that including distiller’s grains in cattle finishing diets at high (40 to 50% of dietary dry matter) inclusion rates may have a negative effect on color stability of strip loins during retail display. Conversely, distiller’s grains could be included in the finishing diets of steers at a low to moderate inclusion level (10 to 25% of dietary dry matter) to maintain, or even enhance, shelf life of steaks in a retail outlet, without affecting cooked beef palatability.

	Footnotes

 
¹ Funding for this project was provided by the Iowa Corn Promotion Board, Johnston, IA.

² Strip loins for this project were obtained from the Univ. of Illinois, Champaign–Urbana and Iowa State Univ., Ames.

³ Correspondence—phone: 612-624-1272; fax: 612-624-4906; e-mail: dicos001{at}umn.edu.

Received for publication October 21, 2004. Accepted for publication June 13, 2005.

	Literature Cited

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Dahlen, C. R., K. A. Hachmeister, C. M. Zehnder, M. E. Dikeman, G. C. Lamb, L. R. Miller, H. Chester-Jones, and A. DiCostanzo. 2001. Influence of feeding malting industry byproducts to feedlot cattle on longissimus muscle sensory traits and tenderness. J. Anim. Sci. 79(Suppl.1):64. (Abstr.)

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