Abstract

We compared strip loins from 24 grass-finished bison on native pasture to 10 grain-finished animals.  All animals in the study  were obtained from three grassland herds belonging to the Nature Conservancy.  The animals were of similar genetic make-up, though the grain-finished bison were 22 months old and the grass-finished bison averaged 32 months in age.  A taste panel compared the grass and grain-fed strip loins for flavor, tenderness, juiciness, and overall acceptability.  The panelists consistently preferred the grain-finished roasts over the grass-finished roasts.  The panelists rated the grain-finished animals equivalent to beef roasts that were used as a negative control.  Significant difference was observed in certain nutrient components between the grass-finished and grain-finished animals.  However, overall grass-finished and grain-finished bison meat is very similar except for total fat and fatty acid profile. 

Introduction

The market for meat is determined by consumer acceptability and nutritional value.  Bison meat has been favored by and has sustained the health of many North American societies for centuries, but today we must measure and prove the nutrient value and palatability attributes of bison meat.   Bison meat is currently marketed as grass-finished or grain-finished.  In this study we compared strip loins from 24 grass-finished animals to 10 grain-finished animals to determine relative palatability and nutrient composition.  All animals were obtained from three grassland herds belonging to the Nature Conservancy: Tall Grass Prairie (Oklahoma), Niobrara Valley (Nebraska), and Ordway Prairie (South Dakota) Preserves.  The selected  sites represent tallgrass and mixed prairie native pastures.   The animals used in the study were of similar genetic make-up.  The grain-finished animals averaged 22 months of age; the grass finished animals averaged 32 months of age.  These are the typical market ages of bison raised under these conditions.   We have previously published work on both grass- and grain-finished animals under more diverse feeding regimens and diverse genetic populations (Driskell et al. 2000; Marchello, et al. 1998; Marchello and Driskell, 2000a,b).

Methods

Boneless bison strip loins (# 180, NAMP, 1997) from 24 grass-finished and 10 grain-finished bison from the Nature Conservancy with similar genetics were used.  The strip loins were vacuum- packaged and stored at -20^oC until utilized.  Each loin was cut into approximately 3 lb. (1.4 kg) roasts.  The frozen roasts were refrigerated overnight.  The next day approximately 3 hours prior to serving time the roasts were placed in cooking bags that had been dusted with one tablespoon of flour.  Six - ½ inch (1.3 cm) slits were cut in the top of each bag.  The roasts in bags were placed in pyrex pans and roasted at 250^oF (121^oC) until the internal temperature reached 160^oF (71^oC).  The roasts were removed and sliced across the grain of the meat into approximately one inch (2.5 cm) cubes, placed on styrofoam (Dow Chemical Co.) plates coded with three-digit random numbers and served immediately for evaluation to panelists seated in individual booths.  Three to four meat samples were presented simultaneously followed by a second set.  Panelists were provided with room-temperature spring water during evaluations.  Panelists evaluated a maximum of 7 samples per setting and a total of 7 settings were needed to complete the evaluation.

Ten to 12 subjects equally divided between men and women from the faculty and staff at NDSU served as panelists.  Panel members received a general explanation of the study and became familiar with the evaluation procedure utilizing a 9 point (1=dislike extremely; 9=like extremely) hedonic scale (AMSA 1995).  The taste panelists evaluated the cooked bison for flavor, tenderness, juiciness, and overall acceptability.

Nutrient composition from the individual cuts of ribeye (longisimus thoracis), top sirloin (gluteus medius), top round (semimembranosus) and shoulder clod (triceps brachii) representing the four major areas of the carcass was analyzed from 24 grass-finished animals and 9 grain-finished animals. 

Approximately one kg of frozen meat samples were shipped to North Dakota State University and stored at -20^oC for later chemical analysis.  All subcutaneous fat was removed prior to lyophilization and homogenization.  Dry matter, crude protein, fat ash, gross energy (total calories), fatty acids, cholesterol, and selected minerals (calcium, iron, sodium) were determined as previously described (Marchello, et al. 1998).  ANOVA and Tukey’s Multiplier range test were used to determine statistical significance between nutrient concentrations of the four muscles analyzed and the palatability profiles (Sokal and Rohlf 1995). 

Results and Discussion

The palatability attributes are shown in Table 1.  The panelists consistently preferred the grain-finished roasts over the grass-finished roasts for all the attributes tested.  Larick et al. (1989) concluded that grain-finished bison exhibits greater amounts of off-flavor and aftertaste than either Hereford or Brahman cattle.  They attributed this to the fatty acid profile especially the phospholipid fraction, which was more abundant in bison.  In a later study Koch et al. (1995) found bison to be more tender and have a different flavor than beef.  In our study taste panelists found no difference between beef and grain-fed bison.  The difference between grain-and grass-finished bison is probably due to both diet and age of the animals.  In a review article by Melton (1990) it was shown that the fat and fatty acid profile of beef affects flavor and palatability characteristics.  Since animals’ feed regimen can influence the palatability of a product we compared the bison roasts from tall grass and mixed grass prairie (Table 2 ) and found no differences in these roasts.

Table 1. Comparison of palatability attributes using the hedonic scale
	Grain-fed	Grass-fed
	(16 roasts)	(24 roasts)
Flavor	7.1	5.1
Tenderness	7.3	4.8
Juiciness	6.7	5.6
Overall acceptability	7.1	4.9
9-point Hedonic Scale: 1=dislike extremely; 9=like extremely.  Grain significantly different from grass (P=0.05).

 

Table 2.  Comparison of palatability attributes of tallgrass and mixed prairie grasses
	Tallgrass	Mixed grass
Attributes	(8 roasts)	(16 roasts)
Flavor	5.3	5.0
Tenderness	4.5	5.0
Juiciness	5.2	5.8
Overall acceptability	4.9	4.9
9-point Hedonic Scale: 1=dislike extremely; 9=like extremely.

The nutrient composition of the raw separable lean cuts from the 24 grass-finished bison and 9 grain-finished bison were averaged and are shown in Table 3.  Grain-finished bison had more protein (21.9% vs 21.3%), more fat (1.4% vs 0.9%), a higher Caloric content (140 vs 131) and a lower moisture content (74.6 % vs 75.6%) than the grass-finished bison.  Mineral and cholesterol content were similar.  In a previous study of grain-finished bison with 100 animals Marchello et al. (1998) found the protein to be 21.7% and fat 2.2%.  Calories, minerals, and moisture content were similar to the present study.  However, Marchello and Driskell (2000a,b) showed that 31 grass-finished animals contained 21.5% protein and 1.7% fat.  Moisture and mineral content as well as caloric values were similar to the present study.  These differences are probably due to the type of rations and the genetic diversity of the bison populations as compared to the present study.  These differences are significant but variable.  However, these differences are probably negligible in terms of  human consumption because of the individual variability of human metabolism.

Comparison of the fatty acid profiles of grain- and grass-finished bison are shown in Table 4.  Considerable difference in most of the fatty acids (expressed as a percentage of total) were observed between the two groups of  meat.   Meat from the grain-finished bison had 5.6% less saturated fat and 3.8% more monounsaturated fat than the grass-finished bison.  No differences were observed in the polyunsaturated fatty acid but the grain-finished animals had 1.6% more of those acids.  This change was not expected.  These differences in fatty acid profiles are due mainly to palmitic, stearic, oleic, linoleic and linolenic acids.

Table 3.  Comparison of nutrient composition of raw separable lean of grain- and grass-finished Bison from the Nature Conservancy
	Grain-finished	Grass-finished
	(%)	(%)
Nutrient	21.9*	21.3*
Protein	74.6*	75.6*
Moisture	1.4*	0.9*
Fat Mineral	1.2	1.2
Cholesterol(mg/100g)	72	66
Food energy (Kcal/100g)	140*	131*
*Means on the same line are significantly different (P<0.05), Tukey test. n=9 for grain-finished, n=24 for grass-finished.

 

Table 4. Comparison of fatty acid profile of raw separable lean from grain- vs. grass-finished bison from the Nature Conservancy
Fatty acid		Percentage
		Grain	Grass
		n=9	n=29
Myristic	(14.0)	0.2	0.3
Pentadecanoic	(15.0)	3.4*	4.5*
Palmitic	(16.0)	14.3*	17.1*
Palmitoleic	(16.1)	1.7	1.9
Margaric	(17.0)	0.7*	2.1*
Stearic	(18.0)	18.4	19.0
Oleic	(18.1)	37.8*	33.6*
Linoleic	(18.2)	16.9*	11.5*
Linolenic	(18.3)	0.2*	3.7*
Eicosenoic	(20.1)	0.1	0.2
Behenic	(22.0)	6.4*	4.4*
Saturated		43.4*	49.0*
Monounsaturated		39.5*	35.7*
Polyunsaturated		17.0	15.4

 *Means on the same line are significantly different (P<0.05), Tukey test.

Previous work (Marchello et al. 1998, Marchello and Driskell 2000a,b) found that grain-finished bison contained 5% less saturated fat, 6% less polyunsaturated fatty acid and 11% more monounsaturated fatty acids than grass finished bison. When we compared the grain-finished animals from the Nature Conservancy to our previous work there is a significant difference in the total content of fat and the fatty acid profile.  The only fatty acids that were not different were margaric and stearic acids.  Consequently there was a 7% difference in monounsaturated fatty acids and a 6% difference in polyunsaturated fatty acids mainly due to the greater amounts of oleic and linoleic acid.  Apparently these differences are due to rations fed to the grain-finished animals.  When we compared the grass-finished animals from the nature conservancy to our previous study on grass, again the only difference was the total fat and some of the individual fatty acids.  Pentadecanoic, palmitoleic, stearic, linoleic, behenic were significantly different.  Thus, there was less variability than what we observed in the grain-finished bison.

Summary

Grain-finished bison tend to be higher in protein and fat and lower in moisture than grass-finished bison.  Specific fatty acids show significant difference.  Taste panelists indicated a preference for grain-finished bison and found it comparable to beef.

Acknowledgments

Funding for this project was provided by the Nature Conservancy.  Appreciation is extended to all support staff who were responsible for doing chemical analysis, statistics, word processing and graphics, Julie Berg, Holly Erdmann, Janet Carlson, Marsha Kapphahn and Arlinda Lewis.

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