Effects of conventional and grass-feeding systems on the nutrient composition of beef

Abstract

The objectives of this study were to determine the nutrient composition of grass-fed beef in the United States for inclusion in the USDA National Nutrient Database for Standard Reference, and to compare the fatty acid composition of grass-fed and conventionally fed (control) beef. Ground beef (GB) and strip steaks (SS) were collected on 3 separate occasions from 15 grass-fed beef producers that represented 13 different states, whereas control beef samples were collected from 3 regions (Ohio, South Dakota, and Texas) of the United States on 3 separate occasions. Concentrations of minerals, choline, vitamin B(12), and thiamine were determined for grass-fed beef samples. Grass-fed GB samples had less Mg, P, and K (P < 0.05), and more Na, Zn, and vitamin B(12) (P < 0.05) than SS samples. Fat color, marbling, and pH were assessed for grass-fed and control SS. Subjective evaluation of the SS indicated that grass-fed beef had fat that was more yellow in color than control beef. Percentages of total fat, total cholesterol, and fatty acids along with trans fatty acids and CLA were determined for grass-fed and control SS and GB. Grass-fed SS had less total fat than control SS (P = 0.001), but both grass-fed and control SS were considered lean, because their total fat content was 4.3% or less. For both GB and SS, grass-fed beef had significantly less (P = 0.001 and P = 0.023, respectively) content of MUFA and a greater content of SFA, n-3 fatty acids, CLA, and trans-vaccenic acid than did the control samples. Concentrations of PUFA, trans fatty acids, n-6 fatty acids, and cholesterol did not differ between grass-fed and control ground beef. Trans-vaccenic acid (trans-11 18:1) made up the greatest concentration of the total trans fats in grass-fed beef, whereas CLA accounted for approximately 15% of the total trans fats. Although the fatty acid composition of grass-fed and conventionally fed beef was different, conclusions on the possible effects of these differences on human health cannot be made without further investigation.

Full text

L. Hoover and M. F. Miller
J. M. Leheska, L. D. Thompson, J. C. Howe, E. Hentges, J. Boyce, J. C. Brooks, B. Shriver,
Effects of conventional and grass feeding systems on the nutrient composition of beef
published online July 18, 2008J ANIM SCI
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RUNNING HEAD: Composition of grain- vs. grass-fed beef1
2
Effects of conventional and grass feeding systems on the nutrient composition of beef1
3
4
J. M. Leheska*, L. D. Thompson*, J. C. Howe, E. Hentges†, J. Boyce*, J. C. Brooks*, B. 5
Shriver*, L. Hoover*, and M. F. Miller2*
6
7
*Texas Tech University, International Center for Food Industry Excellence and 8
Department of Animal and Food Sciences, Lubbock, TX 79409; USDA-ARS-9
BHNRC-Nutrient Data Laboratory, Beltsville, MD 20705; and †USDA Center for 10
Nutrition Policy and Promotion, Alexandria, VA 22302-159411
12
13
1The authors thank the 15 grass-fed beef producers who generously supplied product for this study. In
addition, the authors thank C. Hand and J. Baird for collecting grain-fed beef samples in South Dakota and
Ohio, respectively. Finally, the authors recognize A. M. Luna, K. Adams, J. Clay, J. Koury, and T. Dhin
for many hours spent processing or conducting lab work for this study. This project was funded in part by
beef and veal producers and importers through their $1-per-animal checkoff and was produced for the
Cattlemen’s Beef Board and state beef councils by the National Cattlemen’s Beef Association, USDA
Nutrient Data Lab and Texas Tech University International Center for Food Industry Excellence.
2Corresponding author: mfmrraider@aol.com
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ABSTRACT: The objectives of this study were to determine the nutrient composition of 14
grass-fed beef in the United States for inclusion in the USDA National Nutrient Database 15
for Standard Reference (SR), and to compare the fatty acid composition of grass-fed and 16
conventional-fed (control) beef. Ground beef (GB) and strip steaks (SS) were collected 17
on 3 separate occasions from 15 grass-fed beef producers that represented 13 different 18
states, whereas control beef samples were collected from 3 regions (Ohio, South Dakota,19
and Texas) of the U.S on 3 separate occassions. Concentration of minerals, choline, 20
vitamin B12, and thiamin were determined for grass-fed beef samples. Grass-fed GB 21
samples had less Mg, P, and K (P < 0.05), and more Na, Zn, and vitamin B12 (P < 0.05) 22
than SS samples. Fat color, marbling and pH were assessed for grass-fed and control SS. 23
Subjective evaluation of the SS indicated that grass-fed beef had fat that was more yellow 24
in color than control. Percentage of total fat, total cholesterol, and fatty acids along with 25
trans fatty acids and conjugated linoleic acid (CLA) were determined for grass-fed and 26
control SS and GB. Grass-fed SS had less total fat than control SS (P= 0.001), but both 27
grass-fed and control SS were considered lean, as their total fat content was 4.3% or less. 28
For both GB and SS, grass-fed beef had a significantly lower (P = 0.001 and P = 0.023, 29
respectively) content of monounsaturated fatty acids and a greater content of saturated 30
fatty acids, omega-3 fatty acids, CLA, and trans vaccenic acid than did the control 31
samples. Concentrations of polyunsaturated fatty acids, trans fatty acids, omega-6 fatty 32
acids, and cholesterol did not differ between grass-fed and control ground beef. Trans33
vaccenic acid (18:1, 11t) made up the greatest concentration of the total trans fats in 34
grass-fed beef, whereas CLA accounted for approximately 15% of the total trans fats.35
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Although the fatty acid composition of grass-fed and conventional-fed beef was different,36
conclusions on the possible effects of these differences on human health can not be made 37
without further investigation.38
Key words: beef, conjugated linoleic acid, conventional-fed, fatty acids, grass-fed, 39
nutrient composition40
INTRODUCTION41
Monounsaturated and SFA comprise the largest percentage of fatty acids in beef 42
fat. Furthermore, beef fats are among the richest natural sources of CLA (Chin et al., 43
1992), and trans vaccenic acid (VA), which have been shown to have health benefits 44
(Belury, 2002; Bhattacharya et al., 2006; Huth, 2007). Monounsaturated and omega-3 45
(n-3) fatty acids, aid in reducing the risk of heart disease, while some SFA increase serum 46
cholesterol levels (Groff and Gropper, 1999).47
The types of forage fed to cattle affect gains and carcass characteristics (Allen et 48
al., 1996) and it is well known that crop variety, season, year and geographic location can 49
affect the nutrient content of feedstuffs (Preston, 2004). Therefore, grass-fed beef 50
production in the U.S. is highly variable because of the variety of genetics, forages and 51
management practices utilized, which affect the fatty acid composition of beef 52
(Leonhardt and Wenk, 1997).53
Previous research has shown forage finished cattle produce beef with more CLA 54
and omega-3 fatty acids compared to grain finished beef (Marmer et al., 1984; French et 55
al., 2000). Some studies found grass-fed beef had a lower concentration of MUFA and a 56
higher concentration of SFA compared with grain-fed beef (Melton et al., 1982; Marmer 57
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et al., 1984); however, one study found grass-fed beef had less SFA and more MUFA 58
than grain-fed beef (French et al., 2000). 59
There has been an increase in demand of natural meat products, such as grass-fed 60
beef, partially as a result of consumer interest in the fat content of foods (FMI, 2005). 61
Because of the known variability in grass-fed beef production systems, it is essential to 62
provide consumers with nutrient data for grass-fed beef so an educated purchasing 63
decision can be made. Therefore, the objectives of this study were to determine the 64
nutrient composition of grass-fed beef in the United States for inclusion in the USDA 65
National Nutrient Database for Standard Reference and to compare the fatty acid profile66
of grass-fed and conventional-fed beef.67
68
MATERIALS AND METHODS69
Grass-fed producers completed a screening questionnaire to determine if they 70
qualified to participate in this study. Only producers that indicated that 100% of the cattle 71
diets were made up of native grasses, forages, or cut grasses or forages were allowed to 72
participate. Producers were also screened to determine the types of vitamin and mineral 73
supplements that were provided to their cattle. The majority of the producers in this study 74
indicated using a typical vitamin and mineral supplement while other reported using no 75
supplements at all. Furthermore, producers selected were full-time grass-fed beef 76
producers who were actively selling and marketing their product to restaurants, local 77
retailers, private meat market and via the internet. The key objective to this study was to 78
obtain the most representative sampling of U.S. grass-fed beef in order to produce 79
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compositional data for release in the USDA National Nutrient Database for Standard 80
Reference (SR). SR provides compositional data for foods commonly consumed by 81
Americans. All efforts were made to ensure that the sampling of grass-fed beef in this 82
study was nationally representative of products available to the US population. 83
Protocols for preparing and compositing the meat samples, along with a quality control 84
plan specific to each nutrient to be analyzed were developed in accordance with USDA 85
Nutrient Data Laboratory guidelines. Therefore, all design and sampling procedures for 86
this study were approved by USDA- Nutrient Data Laboratory.87
The second objective of this study was to compare the fatty acid composition of 88
the grass-fed beef samples with conventional beef (control) in the U.S. Therefore, control89
samples were also collected. Conventional beef feeding systems are very standardized 90
throughout the U.S. whereas grass-feeding is not. Therefore, control samples were 91
collected from 3 regions of the country whereas grass-fed samples were collected from 92
15 different producers. 93
Ground beef and strip steaks (derived from IMPS/NAMP 180 Beef Loin, Strip 94
Loin) were collected from 15 grass-fed beef producers representing 13 different states 95
(Alabama, Arkansas, California, Colorado, Georgia, Idaho, Kentucky, Minnesota, 96
Missouri, Montana, New Mexico, Texas, and Virginia) on 3 different occasions.97
Similarly, control beef samples were collected by university personnel from the retail 98
meat case or university meat laboratory in each of three different regions of the country 99
(Lubbock, TX; Brookings, SD; Columbus, OH) on 3 different occasions.100
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A sample collection protocol was provided to all producers and universities who 101
obtained samples for this study. The sample collection protocol required that 2 steaks 102
from 3 different animals be collected by each producer or university on each of 3103
different occasions. All steaks were cut 2.54-cm thick from the 13th rib position of the 104
strip loin (IMPS/NAMP 180 Beef Loin Strip Loins). Likewise, 454 g of ground beef 105
targeting 85% lean and 15% fat (85/15) was to be collected by each producer or 106
university from 3 different carcasses on each of 3 different occasions. However, the 107
specified lean to fat ratio (85/15) was not available from all grass-fed beef producers. 108
When this occurred, the producer was asked to provide samples of the next leanest 109
ground beef (i.e., 88/12) that they had available. Furthermore, 3 producers were unable to 110
provide samples for each sampling period. 111
All samples were vacuum packaged with proper identification, and shipped 112
overnight in an insulated container on dry ice to the Texas Tech University (TTU) 113
Gordon W. Davis Meat Science Laboratory. On delivery, the condition of the package 114
and its content was inspected. Surface temperature of the meat samples was recorded to 115
assure that temperature was maintained at less than -2°C during shipping. Sample 116
weights were also recorded at the time of receipt. Samples were stored at -12°C until 117
sample preparation occurred. Samples that were obtained in Lubbock were purchased 118
fresh (unfrozen), and were identified, vacuum packaged, weighed, and frozen at the TTU 119
Meat Laboratory. All samples were stored and processed in a dark environment to 120
decrease vitamin-B deterioration.121
Ground Beef Samples122
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Frozen packages of ground beef were placed in a cooler at 0 to 4°C to thaw before123
sample preparation. Thawed ground beef samples were frozen in liquid nitrogen and 124
homogenized in a Blixer food processor (model BX 6/6V; Robot Coupe U.S.A, Inc, 125
Jackson, MS) at 1,500 rpm for 10 s and then at 3,500 rpm for 30 s. If a sample did not 126
reach homogeneity the sample was homogenized for an additional 30 s at 3,500 rpm. 127
Once homogeneity was accomplished, aliquots of homogenized samples were placed in 128
labeled Whirl-Pak bags (Nasco, Fort Atkinson, WI). All samples were double bagged. 129
Samples were stored at -80°C until chemical analysis occurred.130
Strip Steak Samples131
Packages of strip steaks were placed in a cooler at 0 to 4°C for 24 h before sample 132
preparation. After thawing, strip steaks were removed from their vacuum packages, 133
placed on a plastic tray, covered with oxygen-permeable film and held in a dark cooler 134
for 90 min before quality assessment. Subjective marbling and lean maturity were 135
evaluated for each sample using USDA Quality Grading standards (USDA, 1997). 136
Subjective fat color score was evaluated for each sample based on the Japanese Meat 137
Grading Association Beef Carcass Grading Standards (JMGA, 2000). Additionally, the 138
pH of the strip steaks was measured using a calibrated IQ 150 Handheld pH meter (IQ 139
Scientific Instruments, Inc., Carlsbad, CA). Following the quality assessment, strip 140
steaks were weighed and dissected. The mean of each quality characteristic within a 141
single sample set from a producers or location was analyzed. 142
The lean, fat, and refuse (connective tissue and scrap) of each steak was separated 143
and weighed individually. Intermuscular and subcutaneous fat, connective tissue, and 144
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any other muscles present were separated from the longissimus muscle. Intermuscular 145
and subcutaneous fat were combined for chemical analyses. Any other muscles and 146
connective tissue that were present were considered scrap and discarded. Cubed strip 147
steak samples were frozen in liquid nitrogen and homogenized in a Blixer food processor148
according to the same protocol as ground beef samples. Aliquots of homogenized 149
samples were placed in labeled Whirl-Pak bags, and all samples were double bagged. 150
Samples were stored at -80°C until analysis.151
Chemical Analyses152
Proximate analyses (percentage of ether extractable fat, protein, and moisture) 153
were conducted at Texas Tech University in the Animal and Food Science Analytical 154
Laboratory. Determination of percent ether extract of each sample was conducted using 155
the Soxhlet method according to Official Method 991.36 (AOAC, 1995). Percent protein 156
in the samples was determined by combustion using a LECO FP 2000 (St. Joseph, MI) 157
following AOAC Official Method 992.15 (Crude Protein in Meat and Meat Products 158
combustion, AOAC, 1995). Percent moisture of samples was analyzed by oven drying 159
according to AOAC Official Method 8.2.1.1 (AOAC, 1995), and percent ash was 160
determined by difference.161
Fatty acids were determined according to AOAC method 996.06 by Covance 162
Laboratory (Madison, WI). Lipids were extracted from 3 g of sample by refluxing 163
for five hours with pentane using a soxhlet extraction apparatus according to AOAC 164
Official Methods 948.22 and 960.39 (Modified) (AOAC, 2000) and saponified with 0.5 N165
methanolic sodium hydroxide and methylated with 14% BF3 methanol. Fatty acid content 166
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was determined by gas chromatography using a SP-2560 column (100 m x 0.25 mm x 0.2 167
micron film thickness) with an injection port temperature of 250°C, a split ration 1:100, a 168
flame ionization detector (FID) set at 300°C: hydrogen 30 mL/min, air 300 mL/min, 169
make up helium 30 mL/min Hydrogen carrier gas, and 1.2 mL/min constant flow. The 170
oven temperature program was set as follows: 170°C hold 5 minutes; increase 2°C /min 171
to 190°C, hold 5 minutes; increase 10°C /min to 210, hold 5 minutes; increase 10°C /min 172
to 230°C, hold 10 minutes. The internal standard used depended on the chain length of 173
the fatty acid in question. Tridecanoic methyl ester (C13:0) was used as the internal 174
standard for regular fatty acids and C23:0 was the internal standard used for long chain 175
fatty acids. Standards were injected with each analysis run, and response factors were 176
calculated. A five point linear regression curve based on the response factors of the 177
injected standard solutions was used to calculate the concentration of the fatty acids in the 178
sample.179
Cholesterol was analyzed using the Direct Saponification – Gas Chromotographic 180
Official Method 994.10 (AOAC, 2000) by Covance Laboratory (Madison, WI). Samples181
were saponofied in 8 mL 50%KOH solution and 40 mL EtOH for 90 min. Saponofied 182
samples were rinsed with 60 mL of EtOH and then 100 mL Toluene was added and 183
mixed vigorously in a separatory funnel. After separation and removal of the polar layer 184
(which occurs after every shake), 40 mL of 0.5 N KOH was added and given a light 185
shake. Three separate additions of 40 mL DiH20 occurs with a light/hard/hard shake 186
sequence. The Toluene passes through a column of Na2SOH salt into a flask which is 187
then capped to complete the extraction. Cholesterol was determined by Gas 188
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Chromatography using a HP-5 column (length of 25 m, a 0.32mm internal thickness with 189
a 0.17 mm film thickness), with helium as the carrier gas (2.1 mL/min with a carrier 190
pressure at 20 atm), and a FID (300°C, 348 ml/min helium flow at 39.4 mL/min and 191
makeup gas flow at 30.4 mL/min). A Split Injector was used with a split ratio of 7.4:1, 192
and a 1.0 mL injection volume with a run time of 40 min.193
Grass-fed beef samples were analyzed for choline at the University of North 194
Carolina by extracting the choline compounds and quantifying by liquid chromatography-195
electrospray ionization-isotope dilution mass spectrometry (Koc et al., 2002). Samples 196
were analyzed for betaine and 5 choline- contributing compounds: free choline (Cho), 197
glycerophosphocholine (GPC), phosphocholine (Pcho), phosphatidylcholine (Ptdcho), 198
and sphingomyelin (SM) (Howe et al, 2004). Total choline content is calculated as the 199
sum of these choline-contributing metabolites (Cho, GPC, Pcho, Ptdcho and SM; Howe 200
et al., 2004). Covance Laboratory (Madison, WI) analyzed samples for thiamin, vitamin 201
B12, Se and other minerals (Ca, Cu, Fe, Mg, Mn, P, K, Na, and Zn) following AOAC 202
Official Methods 942.23, 960.46, 986.15, and 984.27, respectively (2000).203
Quality Control204
To validate all analytical procedures, quality control was monitored by inclusion 205
of certified reference materials and blind duplicates into the sampling stream. Blind 206
duplicates were selected randomly from study samples, aliquoted and labeled according 207
study protocol. A blind duplicate was prepared for every 10 study samples to be 208
analyzed. If the coefficient of variation (CV) of the study sample and its respective blind 209
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duplicate was greater than 10%, the data were considered invalid and reanalyzed. No CV210
was greater than 10% in this study.211
National Institute of Standards and Technology (NIST) Standard Reference 212
Materials (SRM) required by USDA-Nutrient Data Laboratory (NDL) were also 213
prepared for analysis. The SRM identifications were also blinded to the analysts and 214
were analyzed along with study samples. Chemical analyses were considered valid by 215
USDA-NDL when a SRM was within the standard error of the certified value for the 216
respective SRM. Meat homogenate, SRM -1546 (NIST, 2004a) was required to be 217
analyzed for all chemical analyses except selenium. Baby food composite, SRM 2383 218
(NIST, 2002), was used to validate the selenium analysis. Infant formula, SRM 1846 219
(NIST, 2004b), was used to validate determination of vitamin B12 and choline, and peanut 220
butter, SRM 2387 (NIST, 2003), was used for evaluation of thiamin values.221
In addition to the required SRM’s, Beechnut Beef and Poultry baby food 222
homogenates were also analyzed along with all study samples for all chemical analyses 223
according to USDA-NDL protocol. These products do not have a certified value, but do 224
have a database of previous values in which the analyzed samples must fall in order to be 225
considered valid. All data were validated by USDA-NDL staff.226
Data Analyses227
228
Breed type, forage type, management systems, and geographical location were 229
different among producers providing samples. Because all these factors can affect the 230
nutrient composition of the meat, they are considered nuisance variables. Furthermore, 231
this study was not a randomized controlled study as it was impossible to randomly assign 232
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treatment to the animals. Therefore, the F-statistic is not able to be used to assess the 233
significance of the treatment differences. Therefore, permutation analysis (randomized 234
test) was used to test significance of the treatments as it can be used when the F-statistic 235
cannot. All permutation analysis between grass-fed and control beef samples were made 236
using MINITAB  Release 14 (Minitab Inc., State College, PA). In this permutation 237
analysis, 1,000 permuted differences were calculated for each comparison to determine238
whether the magnitude of difference between actual means was a result of chance 239
(variation of data) or whether it was an actual difference that was not likely the result of 240
chance. The permutation analysis P–-value was determined by calculating the proportion 241
of permuted differences that were greater than the actual difference between the original 242
means.243
Quality characteristics along with percentage moisture, fat, protein and ash were 244
statistically evaluated using sampling period (replication) for each producers as the 245
experimental unit. Vitamin and mineral analysis of the grass-fed beef samples were 246
evaluated by composites of producers. Seven composites from individual producers and 4 247
composites of 2 producers each (paired on similar genetics, management practices and 248
region). Cholesterol and fatty acid data were analyzed using producer or university as the 249
experimental unit.250
251
RESULTS AND DISCUSSION252
253
Grass-fed cattle in this study were harvested, on average, at 23 mo of age; 254
however, there was a wide range in the age at harvest (Table 1). The average carcass 255
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weight of the grass-fed cattle was 270 kg, which was substantially less than the average 256
carcass weight of conventional cattle harvested in the U. S. According to the USDA 257
Market Reports (2006), the average weight of U.S. cattle at slaughter was 350 kg in 2005,258
which is greater than the 5-yr average of 341 kg (USDA, 2006).259
Average aging time of the grass-fed strip steaks in this study was 20 d. This is 260
very similar to the 1998 National Beef Tenderness Survey that found average post 261
fabrication aging times for subprimals at the retail level to be 19 d (Brooks et al., 2000). 262
Nonetheless, the 2005 National Beef Tenderness Survey found that average post 263
fabrication aging times for retail subprimals was 23 d (NCBA, 2006). Aging fresh meat 264
allows protein degradation to occur. Therefore, aging time and toughness are negatively 265
correlated (Brooks et al., 2000). The longer cattle are finished on grain, the more tender 266
their meat becomes (Bennett et al., 1995; Leander et al., 1978). Ruhland (2004) and 267
Moeller (1997) indicated that consumers would choose to eat beef more often if they 268
knew it was tender and had a more consistent eating quality. Furthermore, Boleman et 269
al., (1997) found that consumers can differentiate between different tenderness groups of 270
beef and are willing to pay for increased tenderness.271
Quality evaluation (Table 2) of the beef strip steaks indicated that grass-fed beef 272
had more yellow fat and less marbling than did the grain-fed (control) beef. These results 273
were similar to previous studies, which also reported grass-fed beef having a lower 274
marbling score (Bidner et al., 1976; Reagan et al., 1977; Crouse et al., 1984) and fat that 275
was more yellow in color than beef from a conventional feeding system (Bidner et al., 276
1976; Crouse et al., 1984). These differences can be attributed to the difference in the 277
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cattle diets. The fat color can be altered as a result of the higher level of vitamins such as 278
carotene in the forages fed to the cattle or because of changes in the fatty acid profile. 279
Furthermore, grain-fed animals consume a higher energy (higher concentrate) diet which 280
allows excess energy to be used to develop intramuscular fat (marbling).281
There were no differences in lean color measurements or pH between control and 282
grass-fed strip steaks (Table 2). This is contradictory to previous studies which indicated 283
grass-fed beef is darker in color than conventional fed beef (Bidner et al., 1976; Crouse et 284
al., 1984). Furthermore, earlier studies found grass-fed beef to have a higher pH 285
(Furgusen, 2000) than feedlot finished beef (Wulf et al., 1997). The results of the current 286
study may differ because all steaks had been frozen and thawed before quality evaluation.287
Mineral and vitamin analyses were conducted on grass-fed beef samples, and the 288
results are shown in Table 3. Williams et al. (1983) found grass-fed steers, which were 289
leaner than conventional fed animals, had greater concentrations of Zn, Fe, P, Na and K. 290
Ground beef samples had significantly lower levels of Mg, P, and K, and significantly 291
higher levels of Na, Zn and vitamin B12 than did strip steak samples (Table 3). The 292
difference in mineral content may be due to the difference in fat content between the 293
ground beef and strip steak samples (Table 4). Duckett et al. (1993) reported a slight 294
increase in Fe and K content as fat content increased. Variations in mineral content of 295
grass-fed beef were expected, as it is well documented that the level of many trace 296
minerals in feeds is largely determined by the level in the soil where the feeds are grown 297
or by other environmental factors (Preston, 2004).298
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Collection protocol stated ground beef should be 85% lean and 15% fat. 299
Although grass-fed beef producers did not always market 85% lean ground beef, the 300
percentage of fat in grass-fed ground beef (12.8% fat) did not differ from control ground 301
beef (14.2% fat) (Table 4). Furthermore, ground beef samples from grass-fed and control 302
beef did not differ statistically in moisture, protein, or ash (Table 4).303
Numerous studies have reported grass-fed beef to be leaner than conventional 304
raised beef (Melton et al., 1982; Marmer et al., 1984; French et al., 2000). The results of 305
the current study were similar to past studies, which showed control strip steaks had a 306
higher fat content than grass-fed steaks (4.4 and 2.8%, respectively; P = 0.001). This fat 307
difference was due to the higher intramuscular fat (marbling) content of the control steaks 308
as compared to the grass-fed steaks (Table 2). Control steaks also had a lower percent 309
moisture than the grass-fed steaks (P = 0.001). Protein and ash content of strip steaks 310
were unaffected by treatments (Table 4). Previous studies have shown similar results in 311
which increased fat content resulted in a lower moisture content of beef (Reagan et al., 312
1977; Duckett et al., 1993).313
Although control strip steaks had a higher fat content than the grass-fed strip 314
steaks, there was no difference in cholesterol content between the two treatments (Table 315
4). Moreover, grass-fed and control ground beef did not differ in total cholesterol, but 316
ground beef had significantly more cholesterol than did strip steaks (Table 4). Each steak 317
was trimmed of all external fat; therefore, the only fat source was from intramuscular fat. 318
Intramuscular fat has been found to contain less cholesterol than intermuscular fat 319
(Sweeten et al., 1990). Likewise, Eichhorn et al. (1986) determined that adipose tissue 320
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contains about two times as much cholesterol as muscle tissue. Cholesterol data from the321
current study appears to support previous findings that total cholesterol was lower for 322
strip steaks than for ground beef samples (P < 0.05) as the only fat source in the strip 323
steaks was from intramuscular fat.324
The differences on fatty acid composition between grass-fed and control samples 325
were similar for both ground beef and strip steaks. The concentrations of SFA was 326
greater (P = 0.001) and MUFA was lower (P = 0.001) for grass-fed ground beef than that 327
of control ground beef (Table 5). Likewise, grass-fed strip steaks had a greater amount of 328
SFA (P = 0.001) and lower amount of MUFA (P = 0.023) than did control samples 329
(Table 6). These results are similar to previous studies that found grass-fed beef to have 330
more SFA and less MUFA than conventional fed beef (Melton et al., 1982; Marmer et 331
al., 1984) however, more recent studies have found grass-fed beef to have lower SFA 332
than grain-fed beef (French et al., 2000; Yang et al., 2002; Noci et al., 2005). Of the 333
SFA, myristic and palmitic acids have the greatest impact on increasing serum 334
cholesterol, but stearic acid has no effect on blood cholesterol (Ahrens et al., 1957; 335
Hegsted et al., 1965; Keys et al., 1965). Data from the current study illustrate that the 336
difference in SFA was primarily due to a higher concentration of stearic acid (18:0) in 337
grass-fed ground beef compared to control ground beef (P = 0.001; Table 7). Moreover, 338
concentrations of myristic and palmitic acids were not different between grass-fed and 339
control ground beef (Table 7). The ground beef results parallel those of the strip steaks 340
as stearic acid (18:0) in grass-fed strip steaks (17.0 %) was greater (P = 0.003) than the 341
control strip steaks (13.2 %; Table 8). Grass-fed and control strip steak concentrations of 342
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palmitic acids did not differ, but the concentrations of myristic were different (P = 0.02; 343
Table 8). 344
Monounsaturated fatty acids have been shown to have positive health benefits345
(Groff and Gropper, 1999) and MUFA typically makes up nearly half of beef’s fat. Oleic 346
acid made up the greatest concentration of MUFA in both grass-fed and control ground 347
beef and strip steaks (Tables 7 and 8). In both strip steaks and ground beef the control 348
treatment had a greater concentration of oleic acid than did the grass-fed treatment. 349
Grass-fed ground beef and strip steaks had a greater concentration of trans350
vaccenic acid and total CLA (P < 0.001) than control ground beef and strip steaks. The 351
majority of the detectable CLA found in all beef samples was cis-9, trans-11. These 352
results were similar to previous studies that also found CLA content of grass-fed beef to 353
be approximately 2 times greater than grain-fed beef (French et al., 2000; Yang et al., 354
2002; Noci et al., 2005). Moreover, trans vaccenic acid made up the greatest 355
concentration of total trans fats in grass-fed beef. Even so, CLA is the most widely 356
studied naturally occurring trans-fatty acid and has been shown to have positive health 357
benefits (Bhattacharya et al., 2006; Tricon and Yaqoob, 2006). More specifically, CLA, 358
in particular cis-9, trans-11, is believed to have several important physiological functions, 359
including anticarcinogenic, antiatherogenic, immunomodulating, growth promotion and 360
lean body mass promotion (Tanaka, 2005). 361
Two forms of trans-fatty acids are found in foods, man-made and naturally-362
occurring. Man-made trans-fatty acids are formed during hydrogenation of unsaturated 363
fatty acids such as those found in vegetable oils. Naturally-occurring trans-fatty acids are 364
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found in any food product from ruminant animals. Naturally-occurring and man-made 365
trans-fatty acids do not function equally as man-made trans-fatty acids have been 366
associated with higher risk of coronary heart disease (Lopez-Garcia et al., 2005) while, 367
naturally-occurring trans fats have been found to be beneficial to human health (Belury, 368
2002).369
Kepler and others (1966) determined that, Butyrivibrio fibrisolvens, transforms 370
linoleic and linolenic acids to stearic acid in the rumen, which produces CLA as an 371
intermediate. This is why ruminant fats are among the richest natural sources of CLA 372
isomers, in particular the cis-9, trans-11 isomer (French et al., 2000; Chin et al., 1992). 373
The concentration of CLA within ruminants can vary greatly (Mulvihill, 2001). 374
Conjugated linoleic acid concentration in beef products can be altered due to variance in 375
animal diet, cut of meat, season, and genetics (Mulvihill, 2001). 376
There were no difference in total PUFA between grass-fed and control treatments 377
for both ground beef and strip steaks; however, grass-fed ground beef and strip steaks had 378
a higher (P = 0.002) concentration of n-3 fatty acids than did the control samples (Tables 379
5 and 6). This can be attributed to the greater amount of linolenic acid (LNA) and its 380
elongation products in the cattle diets. Furthermore, the n-6/n-3 ratio for control ground 381
beef and strip steaks was greater (P = 0.001) than that of grass-fed ground beef and strip 382
steaks. 383
Studies have established that the n-6 fatty acid, linoleic acid (LA), and the n-3 384
fatty acids, LNA, eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) 385
collectively protect against coronary heart disease (Wijendran and Hayes, 2004). Linoleic 386
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acid is the major dietary fatty acid regulating low-density lipoprotein (LDL)-C 387
metabolism by downregulating LDL-C production and enhancing its clearance 388
(Wijendran and Hayes, 2004). By contrast, n-3 fatty acids, especially EPA and DHA, are 389
potent antiarryhthmic agents (Wijendran and Hayes, 2004), but are typically found in 390
very low levels in beef and other meat. EPA and DHA also improve vascular endothelial 391
function and help lower blood pressure, platelet sensitivity, and the serum triglyceride 392
level (Wijendran and Hayes, 2004). The distinct functions of these two families make the 393
balance between dietary n-6 and n-3 fatty acids an important consideration influencing 394
cardiovascular health (Wijendran and Hayes, 2004). Therefore, Wijendran and Hayes 395
(2004) suggest an adequate achievable intake for most healthy adults to be ~6% en LA, 396
0.75% en LNA, and 0.25% en EPA + DHA, which corresponds to an n-6/n-3 ratio of 397
~6:1. Even so, Wijendran and Hayes (2004) also state the absolute mass of essential fatty 398
acids consumed, rather than their n-6/n-3 ratio, should be the first consideration when 399
contemplating lifelong dietary habits affecting cardiovascular benefit from their intake. 400
Some consumers have been motivated to buy grass-fed beef because sources 401
show that it has a higher n-3 and CLA content than conventional raised beef while also 402
having less fat overall (Melton et al., 1982; Marmer et al., 1984; French et al., 2000). 403
However, the effects of the lipid differences between grass-fed and conventional raised 404
beef, on human health, remains to be investigated. While lean beef has consistently been 405
shown to be beneficial in a cholesterol lowering diet it is still questionable whether or not 406
grass-fed beef would have similar benefits or not. 407
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Table 1. Hot carcass weight and age of grass-fed beef animals at slaughter and the aging 1
time of their strip steaks2
Characteristic N Grass-fed Minimum Maximum
Age, mo 104 23 16 30
HCW, kg 104 271 197 397
Age time, d 1 101220 2 41
1Number of days from slaughter to freezing of beef3
2 The age time for three grass-fed beef animals was not available making n=1014
a5
6
7
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Table 2. Means and standard errors of assessment of fat color, marbling scores, and pH 1
of control and grass-fed beef strip steaks2
Control Grass-fed
Characteristic N1Mean SE N2Mean SE P-value
Fat color39 2.0 0.51 41 3.7 0.16 <0.001
Marbling49 503 17.3 44 420 7.8 <0.001
pH 9 5.6 0.04 44 5.7 0.02 0.525
1 N represents three sample composites from each of three different regions of the 3
country4
2N represents sample composites from each of 15 grass-fed producers. The N for fat 5
color is 41 as there was no fat to assess color on three sample composites6
3Fat color score based on Japanese Beef Carcass Grading Standards; 1 = whitest/lightest 7
colored to 7 = extremely yellow/ darkest colored8
2Marbling score based on USDA Beef Carcass Grading Standards(USDA, 2006): 300 = 9
Slight00, 400 = Small00, 500 = Modest00.10
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Table 3. Vitamin and mineral content of raw strip steak and ground beef from grass-fed 1
beef. Values are per 100 g of edible portion.2
Strip Steaks
(n = 11) 1
Ground Beef
(n = 11) 1
Nutrient Mean SE Mean SE
P-value
Ca, mg 8.7 0.704 11.6 1.260 0.044
Cu, mg 0.070 0.004 0.065 0.002 0.407
Fe, mg 1.9 0.091 2.0 0.072 0.253
Mg, mg 23.1 0.282 18.5 0.347 0.001
Mn, mg 0.009 0.0004 0.010 0.0006 0.619
P, mg 211.9 1.94 174.8 3.2 0.001
K, mg 342.4 1.72 288.5 5.61 0.001
Se, µg 21.2 5.30 15.3 3.76 0.337
Na, mg 55.0 1.01 68.2 1.90 0.001
Zn, mg 3.6 0.141 4.6 0.127 0.001
Thiamin, mg 0.052 0.0019 0.050 0.0015 0.515
Vitamin B12, µg 1.3 0.120 2.0 0.078 0.001
Total Choline, mg 65.1 1.87 67.7 1.87 0.327
17 Samples were composites of individual grass-fed animals from a single producer, and 3
4 samples were composites of animals from two different producers (8 producers total) 4
that were identified to have similar genetics, management practices and be from the same 5
region of the country. These composites were approved by USDA-Nutrient Data Lab. 6
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Table 4. Means and standard errors of the means for percentage moisture, fat, protein, and ash, and cholesterol content of raw 1
strip steaks and ground beef from grain-fed (control) and grass-fed treatments 2
Strip Steaks Ground Beef
Control
(n = 9)
Grass-fed
(n = 41) 1
Control
(n = 9)
Grass-fed4
(n = 42) 2
Constituent
Mean SE Mean SE
P-value
Mean SE Mean SE
P-value
Moisture, % 71.6 0.25 73.5 0.19 0.001 65.9 0.64 67.1 0.47 0.772
Fat, % 4.4 0.41 2.8 0.17 0.001 14.7 0.80 12.8 0.58 0.800
Protein, % 23.2 0.15 23.1 0.12 0.613 19.2 0.17 19.4 0.15 0.511
Ash, % 0.8 0.09 0.7 0.06 0.655 0.4 0.13 0.8 0.09 0.093
Cholesterol, mg/100 g3 54.6 1.25 54.7 0.90 0.987 62.0 1.08 62.3 0.83 0.851
1Sample size represents, 3 composite samples from 13 grass-fed producers and 1 composite sample from 2 grass-fed 3
producers (n=41)4 2Sample size represents, 3 samples from 13 grass-fed producers, 2 composite samples from a single producer and 1 composite 5
sample from another grass-fed producer (n =42)6 3 Cholesterol sample size represents a single composite for each grass-fed producer (n=14 for strip steaks and n=15 for ground 7
beef), and a single composite for each region (n = 3) in which the control samples were collected. 8
9
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Table 5. Mean concentration of saturated, unsaturated, trans, omega-3 (n-3) and omega-1
6 (n-6) fatty acids in grass-fed and control raw ground beef as percentage of total fatty 2
acids (g/100 g fat)3
Control Grass-fed
Fatty acid Mean SE Mean SE P-value
SFA
1
44.5 0.75 50.9 0.60 0.001
MUFA
2
47.0 1.09 39.2 0.74 0.001
PUFA
3
2.7 0.10 2.44 0.20 0.276
n-3 0.24 0.04 0.88 0.06 0.002
n-6 2.20 0.17 1.85 0.10 0.195
Total trans
4
6.00 1.02 7.15 0.32 0.194
c9, t11 CLA 0.50 0.04 0.94 0.04 0.001
Total CLA 0.60 0.04 1.03 0.04 0.001
PUFA:SFA 0.059 0.004 0.050 0.004 0.904
n-6:n-3 9.60 1.44 2.45 0.39 0.001
1 Total saturated fatty acid =  8:0, 10:0, 12:0, 14:0, 15:0, 16:0, 17:0, 18:0, 20:04
2 Total monounsaturated fatty acid = 9c 14:1, 14c 15:1, 9c 16:1, 10c 17:1, 11c 20:1, 5
13c 22:1, 9c 18:1, 11c 18:1, 12c 18:1, 13c 18:1, 14c 18:1, 15c 18:16
3 Total polyunsaturated fatty acid =  18:2, 18:3 n-6, 18:4, 20:2 n-6, 20:3, 20:4, 20:5 n-3, 7
22:5 n-3, 22:6 n-6 8
4 Total Trans fatty acid =  5t18:1; 6t,8t18:1; 9t18:1; 10t 18:1; 11t18:1; 12t18:1; 9
13t,14t18:1; 16t18:1; trans 18:210
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Table 6. Mean concentration of saturated, unsaturated, trans, omega-3 (n-3) and omega-1
6 (n-6) fatty acids in grass-fed and control raw strip steaks as percentage of total fatty 2
acids (g/100 g fat)3
Control Grass-fed
Fatty acid Mean SE Mean SE P-value
SFA
1
45.1 0.50 48.8 0.53 0.002
MUFA
2
46.2 0.90 42.5 0.60 0.023
PUFA
3
2.77 0.25 3.41 0.19 0.129
n-3 0.19 0.01 1.07 0.11 0.002
n-6 2.58 0.25 2.30 0.13 1.000
Total trans
4
6.04 0.99 5.30 0.25 0.294
c9, t11 CLA 0.38 0.03 0.66 0.07 0.093
Total CLA 0.48 0.04 0.85 0.04 0.001
PUFA:SFA 0.061 0.005 0.070 0.004 0.341
n-6:n-3 13.6 1.55 2.78 0.64 0.001
1 Total saturated fatty acid =  8:0, 10:0, 12:0, 14:0, 15:0, 16:0, 17:0, 18:0, 20:04
2Total monounsaturated fatty acid =  9c 14:1, 14c 15:1, 9c 16:1, 10c 17:1, 11c 20:1, 5
13c 22:1, 9c 18:1, 11c 18:1, 12c 18:1, 13c 18:1, 14c 18:1, 15c 18:16
3 Total polyunsaturated fatty acid =  18:2, 18:3 n-6, 18:4, 20:2 n-6, 20:3, 20:4, 20:5 n-3, 7
22:5 n-3, 22:6 n-6 8
4 Total Trans fatty acid =  5t18:1; 6t,8t18:1; 9t18:1; 10t 18:1; 11t18:1; 12t18:1; 9
13t,14t18:1; 16t18:1; trans 18:2.10
11
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Table 7. Grass-fed and control raw ground beef fatty acid profile shown as percentage of 1
total fatty acids (g/100 g fat)2
Control Grass-fed
Fatty acid Common name Mean SE Mean SE P-value
8:0 Caprylic 0.010 0.005 0.007 0.002 0.563
10:0 Capric 0.039 0.002 0.051 0.002 0.018
12:0 Lauric 0.077 0.003 0.088 0.003 0.173
14:0 Myristic 3.26 0.102 3.23 0.095 0.915
9c 14:1 Myristicoleic 0.886 0.039 0.660 0.049 0.068
15:0 Pentadecanoic 0.550 0.039 0.751 0.035 0.038
14c 15:1 Pentadecenoic 0.00 0.000 0.015 0.015 --
16:0 Palmitic 25.3 0.321 25.90 0.196 0.277
9c 16:1 Palmitoleic 3.91 0.177 3.21 0.116 0.021
17:0 Heptadecanoic 1.43 0.153 1.42 0.037 0.910
18:0 Stearic 13.7 0.670 19.2 0.653 0.001
5t 18:1 0.016 0.002 0.014 0.002 0.732
6t,8t 18:1 0.333 0.043 0.215 0.017 0.012
9t 18:1 Elaidate 0.393 0.040 0.282 0.022 0.093
10 t 18:1 2.69 1.11 0.752 0.054 0.001
11t 18:1 Vaccenic 1.14 0.195 4.14 0.247 0.001
12 t 18:1 0.173 0.012 0.209 0.016 0.299
13t, 14t 18:1 0.434 0.030 0.601 0.031 0.039
16t 18:1 0.140 0.019 0.328 0.016 0.001
9c 18:1 Oleic 40.0 0.866 33.1 0.550 0.001
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11c 18:1 Cis-Vaccenic 1.77 0.072 1.16 0.038 0.002
12c 18:1 0.276 0.015 0.194 0.017 0.050
13c 18:1 0.576 0.041 0.302 0.020 0.001
14c 18:1 0.162 0.009 0.255 0.014 0.012
15c 18:1 0.241 0.0143 0.217 0.016 0.445
trans 18:2 0.677 0.014 1.29 0.074 0.001
18:2 Linoleic 2.09 0.166 1.71 0.985 0.112
18:3 n-3 Linolenic 0.207 0.022 0.676 0.049 0.001
18:4 Octadecatetraeonic 0.000 0.000 0.018 0.007 --
20:0 Arachidic 0.095 0.009 0.184 0.012 0.007
11c 20:1 Eicosenoic 0.205 0.010 0.139 0.007 0.001
20:2 n-6 Eicosadienoic 0.025 0.014 0.012 0.005 0.368
20:3n-6 Eicosatrienoic 0.000 0.000 0.011 0.004 --
20:4n-6 Arachidonic 0.077 0.011 0.129 0.008 0.021
20:5 n-3 Eicosapentaenoic 0.000 0.000 0.013 0.005 --
22:0 Behenic 0.000 0.000 0.035 0.004 --
22:5 n-3 Docosapentaenoic 0.034 0.017 0.1581 0.012 0.002
22:6 n-3 Docosahexaenoic <1 . <1 . --
1
2
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1
Table 8. Grass-fed and control raw strip steak fatty acid profile shown as percentage of 2
total fatty acids (g/100 g fat)3
Control Grass-fed
Fatty acid Common name Mean SE Mean SE P- value
10:0 Capric 0.058 0.002 0.04 0.008 0.301
12:0 Lauric 0.071 0.006 0.05 0.009 0.271
14:0 Myristic 3.45 0.090 2.84 0.117 0.020
9c 14:1 Myristicoleic 0.821 0.007 0.55 0.039 0.001
15:0 Pentadecanoic 0.487 0.033 0.54 0.021 0.233
16:0 Palmitic 26.3 0.573 26.9 0.337 0.465
9c 16:1 Palmitoleic 3.81 0.091 3.27 0.126 0.060
17:0 Heptadecanoic 1.36 0.101 1.23 0.038 0.219
18:0 Stearic 13.2 0.385 17.0 0.514 0.003
6t,8t 18:1 0.382 0.047 0.15 0.0191 0.004
9t 18:1 Elaidate 0.355 0.016 0.27 0.017 0.054
10 t 18:1 3.60 0.794 0.60 0.042 0.002
11t 18:1 Vaccenic 0.510 0.069 2.95 0.174 0.001
12 t 18:1 0.191 0.024 0.17 0.019 0.489
13t, 14t 18:1 0.385 0.034 0.46 0.037 0.357
16t 18:1 0.101 0.007 0.24 0.015 0.001
9c 18:1 Oleic 38.6 0.814 36.5 0.444 0.044
11c 18:1 Cis-Vaccenic 1.63 0.052 1.24 0.030 0.001
12c 18:1 0.318 0.049 0.18 0.023 0.021
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13c 18:1 0.489 0.020 0.32 0.017 0.001
14c 18:1 0.109 0.003 0.19 0.014 0.011
15c 18:1 0.238 0.011 0.17 0.022 0.090
trans 18:2 0.517 0.058 1.01 0.07 0.002
18:2 Linoleic 2.375 0.207 2.01 0.106 0.161
18:3 n-3 Linolenic 0.128 0.008 0.71 0.064 0.001
20:0 Arachidic 0.077 0.004 0.132 0.009 0.024
11c 20:1 Eicosenoic 0.171 0.017 0.14 0.007 0.032
20:2 n-6 Eicosadienoic 0.012 0.012 0.01 0.0048 0.757
20:4n-6 Arachidonic 0.193 0.033 0.31 0.044 0.222
22:5 n-3 Docosapentaenoic 0.059 0.009 0.24 0.028 0.013
22:6 n-3 Docosahexaenoic <1 . <1 . --
1
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Citations
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