Introduction
Ground beef is considered one of the major sources of animal protein in the United States, and is one of the most widely consumed beef commodities across the United States. In most US retail stores, consumers can choose between grain-fed and grass-fed ground beef, but consumers prefer grain-fed ground beef due to the flavor and overall palatability gained on a grain-based diet (Wood et al., 2003). However, sustainable production, animal welfare, and low-fat products often drive consumer purchasing decisions, resulting in an increased demand for grass-fed ground beef (United States Department of Agriculture, Agriculture Marketing Service [USDA-AMS], 2007).
To date, there are no federal standards regarding grass-fed labeling (USDA-AMS, 2016). However, there are several ways to label grass-fed meat. According to the American Grassfed Association (AGA, 2018) and its Grassfed Ruminant Standards, a grass-fed beef cattle program requires that ruminant animals are strictly fed grass and forage as their sole energy sources of feed. Cattle must have continuous access to open pasture from birth to the finishing stage (AGA, 2018). Meat products from animals following AGA guidelines are permitted to be marketed as AGA grass-fed meat.
It is recommended an omega-6:omega-3 ratio (4:1) to help decrease unfavorable health conditions (Simopoulos, 2002). Grass-fed ground beef contains 3 times more omega-3 fatty acids than traditional grain-fed ground beef; however, there is no evidence to support that choosing grass-fed beef is a healthier choice for consumers compared to traditional ground beef (Smith, 2013). From an economic point of view, grass-fed beef has a relatively higher price than grain-fed beef. For instance, the USDA-AMS National Monthly Grass Fed Beef Report (USDA-AMS, 2018) reported that commodity ribeye steaks averaged $3.62/kg at the retail store while the grass-fed premium was priced 2.37 times higher. Researchers have studied the differences in flavor profiles between grass-fed and grain-fed beef and have found that grass-fed beef has a negative effect on consumer flavor acceptability (Killinger et al., 2004; Kerth et al., 2007; Mandell, 1998). Additionally, beef that has been produced on grass have a different fatty acid composition, including a higher proportion of polyunsaturated fatty acids (PUFA) than grain-fed cattle, which can decrease flavor desirability of meat (Melton, 1990). The overall objective of this study was to evaluate consumer acceptance of grass-fed ground beef compared to commodity and Angus ground beef.
Materials and Methods
Product preparation
For this study, 80% lean and 20% fat vacuum packaged chubs of Angus, commodity, and 85% lean and 15% fat frozen chubs of grass-fed ground beef, were purchased from a local retail store in Manhattan, KS. As a result, the postmortem age and supplier of the ground beef was unknown. All products were labeled as “Product of U.S.” The term “commodity” is used to define USDA Select meat, which is commonly found in retail stores throughout the United States as the common beef for everyday use (Griffin and Savell, 2018). Grass-fed ground beef was labeled as “Meat from animals 100% grass-fed.” For each treatment, replicates (n = 14) from different production lots with each replicate consisting of 2.26 kg-bag were used. Upon arrival, product was stored in their original packaging in a –40°C research freezer for up to 30 d in the Kansas State University (KSU) Meat Laboratory. The ground beef was thawed for 24 h at 2 to 4°C. Two 113-g ground beef patties with a thickness between 1.10 and 1.27 cm (AMSA, 2016) were formed from each independent unit, packed separately, and used for consumer evaluation. Ground beef patties were manually formed using an acrylic patty former with round template that was 10.80 cm in diameter. After patty manufacturing, samples were placed on trays, crust frozen, and then vacuum packaged and stored at –40°C until used for panels. The remaining product was vacuum packaged, frozen at –40°C until analyzed for proximate analysis and fatty acid (FA) profile determination.
Consumer sensory evaluation
Consumer sensory panels were conducted in Weber Hall at KSU, Manhattan, KS, following the AMSA research guidelines (AMSA, 2016). Ground beef chubs were thawed for 24 h at 2 to 4°C prior to sensory evaluation. Consumer panelists (n = 98) were recruited from Manhattan, KS, and adjacent communities. This study was conducted over six 1-h sessions and 18 panelists were present at each panel session. Electronic tablets (Model 5709 HP Steam 7; Hewlett-Packard, Palo Alto, CA) were provided to consumers to record a panelist response (Qualtrics Software, Provo, UT). In addition, panelists were provided with a napkin, plastic fork, plastic knife, expectorant cup, glass of water, and 3 unsalted crackers and apple juice to be used to clear their palate in between each sample. Panelists completed a demographic survey, which included general questions on age, sex, income, etc., and they were asked to give information about their knowledge on Omega-3 rich ground beef products and if they were willing to pay extra for this commodity. These data was loaded onto the tablet and used the ballot pages on the tablet for each sample to be evaluated. Ground beef patties were cooked on a clamshell grill (Cuisinart Griddler Deluxe, Model GR-150, East Windsor, NJ) to an internal temperature of 74°C using a probe thermometer (Super-Fast Thermopen, ThermoWorks, American Fork, UT). Following cooking, ground beef patties were manually cut with a knife into 4 wedge-shaped pieces. One piece was placed on a coded paper plate. Each panelist evaluated 6 samples (2 per treatment) in a random order. Each panelist evaluated samples using a continuous line scale anchored at both ends with descriptive terms. Ground beef patties were evaluated for tenderness, juiciness, flavor liking, texture liking, and overall liking. For all samples, the 0 anchors were set as extremely tough, extremely dry, and dislike extremely; the 50 anchors were labeled as neither tough nor tender, neither dry nor juicy, and neither like nor dislike; and the 100 anchors were identified as extremely tender, extremely juicy, and like extremely. Additionally, consumers rated each sample as either acceptable or unacceptable for each sensory trait assessed.
pH and proximate analysis
A calibrated pH probe (Model FC232, Hanna Instruments Inc., Woonsocket, RI) with a pH meter (Model HI 99163, Hanna Instruments Inc.) was inserted in duplicate to determine the pH of ground beef. Each sample of ground beef treatments was prepared for moisture, fat, and protein (proximate analysis) determination by freezing pieces of the samples through immersion in liquid nitrogen, homogenizing the frozen pieces using a blender (Model 33BL79, Waring Products, New Hartford, CT) and placing the powdered sample in 11.4 × 22.9 cm plastic labeled Whirl-Pak bags (Fisher Scientific, Fair Lawn, NJ). The homogeneous powder was stored at –80°C until used for proximate analysis determination. The Association of Analytical Communities procedures (AOAC Official Method PVM-1:2003 MEAT) were used to analyze moisture and crude fat content by the SMART system 5 (CEM Corp., NC). Protein analysis was conducted using the LECO FP-2000 Protein/Nitrogen Analyzer (Model 602–600, LECO Corp., St. Joseph, MI). The combustion method (TruMac N Nitrogen/Protein determination Instruction manual, 2014, LECO Corp.) was used. The percent of nitrogen was then multiplied by 6.25 to determine protein content.
Fatty acid methyl ester analyses
Homogeneous powder from each treatment were used for fatty acid methyl ester (FAME) determination. This procedure was performed as described by Sukhija and Palmquist (1988), which utilizes a 1-step extraction/transesterification method. Briefly, a 200 mg freeze-dried ground beef sample was used and transesterified in methanol:benezene:acetyl chloride (20:27:3, vol/vol) and 2 mL of internal standard (methyl tridecanoate; 2.0 mg of fatty acid C:13:0/mL of benzene). Agilent Gas Chromatograph (model 7890A; Agilent Technologies, Inc., Santa Clara, CA) was utilized to determine FAME. The gas chromatograph machine was equipped with a 100 m × 0.25 mm × 0.20µ (id) fused silica capillary column (SP-2560 Supelco Inc., Bellefonte, PA). Column oven temperature was held at 100°C for 5 min, increased to 240°C at a rate of 3°C/min, and held for 20 min at 240°C. Injection and detector temperature were 250°C with a flow rate of 1 mL/minute. A genuine external standard Supelco 37 (47885-U Supelco; Sigma-Aldrich, St. Louis, MO) was used to identify individual FA after comparing retention times. Subsequently, individual FAME were calculated as a percentage of total FAME. To quantify total FA content, an internal standard is recommended according to the Sukhija and Palmquist method (Sukhija and Palmquist, 1988). Additionally, conjugated linoleic acid (CLA) isomers were identified with an extra composite standard mix of CLAs, C18:1 cis-11, and C18:1 trans-11 (Matreye #s 1255, 1257, 1256, 1254, 1267, 1263). This standard was not quantitative and was used for peak ID only. Response factor (RF) for all CLAs was taken from the C18:2 peak average in the 37 FAME standard and RF for C18:1 cis-11 and C18:1 trans-11 were taken from C18:1 cis-9 and C18:1 trans-9, respectively. The C18:1 trans-isomers were not well separated and were used for considered estimates. DPA (C22:5 n-3) was identified at an earlier date using a Marine PUFA standard (Sigma #47033) and uses the same RF as DHA (C22:6 n-3).
Statistical analysis
Data were analyzed using SAS version 9.4 (SAS Inst. Inc., Cary, NC). Treatment effects were evaluated using the PROC GLIMMIX procedure in SAS. Data were analyzed as a complete block design with each chub from each treatment treated as the blocking factor. In the model, the Kenward–Roger approximation was utilized. If a treatment effect was found to be significant (P < 0.05), the PDIFF option was used for mean separation. Additionally, a binomial model was used to analyze consumer acceptability scores. Differences were considered significant at (P < 0.05) The CORR procedure of SAS was used to determine Pearson correlation coefficients.
Results and Discussion
Consumer demographics
The demographic characteristics of the 98 consumers who evaluated the ground beef samples are shown in Table 1. More men (59%) than women (41%) participated in the sensory panel. More than 60% of all participants were Caucasian/white and 55.3% were single. More than 50% of consumers (51.6%) had an annual household income of $75,000 or more. In addition, 72.2% of consumers who were surveyed had some college/technical experience, completed college, or post graduate experience. Just over 35% of the consumers (36.5%) were aged 18 to 24 yr old. More than 87.3% of panelists consumed a ground beef product from 4 to 21 times per week. When asked if they were aware of omega 3s, 69.1% responded that they were, and 79.6% responded that they would be willing to pay extra ($0.86 ± $0.49) to purchase omega 3 rich ground beef products.
Demographic characteristics of consumers (n = 98) who participated in sensory panels to analyze Angus, commodity, and grass-fed ground beef samples
| Characteristic | Response | Percentage of consumers |
| Gender | Male | 59.0 |
| Female | 41.0 | |
| Household size | 1 person | 16.7 |
| 2 people | 21.9 | |
| 3 people | 17.7 | |
| 4 people | 22.9 | |
| 5 people | 8.3 | |
| 6 people | 6.3 | |
| Over 6 people | 6.3 | |
| Marital status | Single | 55.3 |
| Married | 44.7 | |
| Age group | 18 to 24 | 36.5 |
| 25 to 34 | 11.5 | |
| 35 to 44 | 11.5 | |
| 45 to 54 | 16.7 | |
| 55 to 64 | 18.8 | |
| Greater than 65 | 5.2 | |
| Ethnic origin | African-American | 14.6 |
| Asian | 1.0 | |
| Caucasian/White | 62.5 | |
| Hispanic | 5.2 | |
| Native American | 5.2 | |
| Other | 2.1 | |
| Mixed Race | 9.4 | |
| Annual household income, $ | < $25,000 | 10.5 |
| $25,000 to $34,999 | 7.4 | |
| $35,000 to $49,999 | 14.7 | |
| $50,000 to $74,999 | 15.8 | |
| $75,000 to $99,999 | 15.8 | |
| $100,000 to $149,999 | 19.0 | |
| $150,000 to $199,999 | 10.5 | |
| > $199,999 | 6.3 | |
| Highest level of education completed | Non-high school graduate | 5.2 |
| High school graduate | 22.7 | |
| Some college/technical school | 42.3 | |
| College graduate | 16.5 | |
| Post graduate | 13.4 | |
| Weekly ground beef consumption | 0 to 3 times | 12.8 |
| 4 to 6 times | 27.7 | |
| 7 to 9 times | 14.9 | |
| 10 to 12 times | 21.3 | |
| 13 to 15 times | 20.2 | |
| 16 to 18 times | 2.1 | |
| 19 to 21 times | 1.1 | |
| Were consumers aware of omega 3s? | Yes | 69.1 |
| No | 30.9 | |
| Were consumers willing to pay a premium for nutritionally better with omega 3s? | Yes | 79.6 |
| No | 20.4 | |
| Avg. perception of health benefits (0 = no benefit; 100 = extremely beneficial): 71.9 ± 21.1 | ||
| Avg. premium willing to pay: $0.86 ± $0.49 | ||
Consumer sensory evaluation
Least squares means for consumer palatability ratings for each treatment of ground beef are found in Table 2. Angus and commodity ground beef were rated higher (P < 0.05) for overall liking compared to grass-fed ground beef. Consumers found tenderness and juiciness palatability ratings to be similar (P > 0.05) for all 3 types of ground beef. The percentage of ground beef samples rated as acceptable for each trait by consumers is shown in Table 3. Consumers preferred (P < 0.05) Angus over grass-fed ground beef with a flavor acceptability of 83.3 and 73.9%, respectively; and 94.9 and 82.5%, respectively, for overall acceptability. Commodity ground beef had a similar (P > 0.05) flavor acceptability and overall acceptability to Angus and grass-fed ground beef. Consumers indicated no difference (P > 0.05) for tenderness acceptability, juiciness acceptability, and texture acceptability among the 3 ground beef treatments. It is well documented the flavor differences between corn-based and grass-fed meat (Hedrick et al., 1983; Crouse et al., 1984; Rouquette et al., 2014). Particularly, grass-fed beef had a different fatty acid composition than grain-fed cattle, which altered palatability attributes such as flavor (Melton, 1990). These results were also similar as those found by O’Quinn et al. (2016), who reported that ground beef from conventionally raised cattle was more desirable than grass-fed cattle.
Least squares means for consumer (n = 98) palatability ratings1 for Angus, commodity, and grass-fed ground beef
| Treatment | Tenderness | Juiciness | Flavor liking | Texture liking | Overall liking |
| Angus | 64.7 | 69.7 | 59.8 | 63.2 | 65.2a |
| Commodity | 66.5 | 68.0 | 61.2 | 61.5 | 66.2a |
| Grass-fed | 64.0 | 65.9 | 54.1 | 57.2 | 56.4b |
| SEM2 | 2.07 | 1.96 | 2.15 | 2.1 | 2.12 |
| P-value | 0.57 | 0.40 | 0.06 | 0.06 | < 0.01 |
a,bMeans in the same column lacking a common superscript differ (P < 0.05).
1Sensory scores: 0 = not tender/juicy, dislike flavor/texture/overall extremely; 50 = neither tough nor tender, neither dry nor juicy, or neither like nor dislike flavor/texture/overall; 100 = very tender/juicy, like flavor/texture/overall extremely.
2Pooled standard error of the least squares means.
Percentage of Angus, commodity, and grass-fed ground beef samples considered acceptable for palatability traits by consumers (n = 98)
| Treatment | Tenderness acceptability | Juiciness acceptability | Flavor acceptability | Texture acceptability | Overall acceptability |
| Angus | 91.6 | 92.4 | 83.3ab | 90.5 | 94.9a |
| Commodity | 84.7 | 91.4 | 90.6a | 83.8 | 91.8ab |
| Grass-fed | 84.7 | 87.4 | 73.9b | 83.8 | 82.5b |
| SEM1 | 4.27 | 3.84 | 4.47 | 4.88 | 4.11 |
| P-value | 0.26 | 0.46 | 0.02 | 0.28 | 0.03 |
a,bMeans in the same column lacking a common superscript differ (P < 0.05).
1Pooled standard error of the least squares means.
pH and proximate analysis
Ground beef proximate composition and pH results are presented in Table 4. Commodity beef pH was greater (P < 0.01) than Angus, and both grain-fed treatments had higher (P < 0.01) than grass-fed. Conversely, other studies demonstrated grass-finished beef had higher pH than grain-finished beef (Wulf et al., 1997; Rouquette et al., 2014). The label of commodity ground beef stated the addition of lean finely textured beef, which increases the ultimate pH of beef due to high ammonia levels used in the process to separate lean from fat. In addition, the use of different muscles, including muscles from the chuck and round, in manufacturing ground beef can also affect its ultimate pH (Von Seggern et al., 2005). Troutt et al. (1992) found no differences in pH between raw ground beef patties containing 15 and 20% fat. Treatment had no effect on moisture content (P > 0.05) or fat content (P > 0.05). Packages of ground beef used in this study stated that Angus and commodity ground beef was 80% lean (containing 20% fat). Grass-fed ground beef, however, was packaged with a label stating 85% lean (containing 15% fat). After examining fat content levels, the results indicated Angus, commodity, and grass-fed ground beef had 19.83, 19.81, and 15.78% fat content, respectively. These findings are in compliance with the 20% deviation limit for ground beef label claims on fat content (Howe et al., 2007). In a similar study, Melton et al. (1982a) found no significant differences for moisture or fat content between ground beef from grass-fed and grain-fed cattle. However, Rouquette et al. (2014) found moisture content of longissimus steaks from grass-fed cattle was higher than those from grain-finished cattle. Treatment had no effect (P > 0.05) on protein content. Similarly, O’Quinn et al. (2016) reported no statistical differences between grain-fed and grass-fed ground beef for protein content.
Moisture, fat, protein content, and pH of Angus, commodity, and grass-fed ground beef
| Treatment | Fat, % | Moisture, % | Protein, % | pH |
| Angus | 19.8 | 61.5 | 18.0 | 5.8b |
| Commodity | 19.8 | 61.6 | 17.6 | 6.0a |
| Grass-fed | 15.7 | 64.7 | 18.7 | 5.6c |
| SEM1 | 1.48 | 1.08 | 0.34 | 0.04 |
| P-value | 0.16 | 0.12 | 0.15 | < 0.01 |
a–cLeast squares means for the same product in the same column lacking a common superscript differ (P < 0.05).
1Pooled standard error of the least squares means.
Fatty acids
Saturated fatty acids.
Fatty acid profiles of ground beef from 3 sources are summarized in Table 5. In the current study, the SFA with the greatest proportion in the samples across all treatments were: myristic acid (14:0), palmitic acid (16:0), and stearic acid (18:0). Mean squares indicate that samples of ground beef from the 2 grain-fed treatments had greater (P < 0.05) total saturated fatty acids (SFA) than grass-fed samples. Grain-fed ground beef treatments had higher (P < 0.05) proportions for 14:0 and 18:0 than grass-fed; however, there were no differences (P > 0.05) for 16:0 across all treatments. Many studies reported similar results for 14:0 on longissimus steaks (Realini et al., 2004). In addition, Melton et al. (1982a) indicated an increase of 18:0 and a decrease of 16:0 proportion in ground beef from grass-fed cattle compared with grain-fed ground beef. It is noteworthy that depending on the muscles used for ground beef production, the fatty acid profile may vary within a beef carcass (Alfaia et al., 2007).
Least squares means of percentage of fatty acids in Angus, commodity, and grass-fed ground beef
| Fatty acid | Treatment | SEM1 | P-value | ||
| Grass-fed | Commodity | Angus | |||
| 8:0 | 0.01 | 0.01 | 0.01 | < 0.01 | 0.77 |
| 10:0 | 0.05c | 0.06a | 0.05b | < 0.01 | < 0.01 |
| 12:0 | 0.08b | 0.09a | 0.09a | < 0.01 | < 0.01 |
| 14:0 | 3.18b | 3.41a | 3.44a | 0.03 | < 0.01 |
| 14:1 | 1.15a | 0.95b | 0.98b | 0.03 | < 0.01 |
| 15:0 | 0.48b | 0.54a | 0.53a | 0.01 | < 0.01 |
| 15:1 | 0.02a | 0.01b | 0.01b | < 0.01 | < 0.01 |
| 16:0 | 26.05 | 26.233 | 26.31 | 0.12 | 0.30 |
| 16:1 | 4.67a | 4.84b | 4.92b | 0.09 | < 0.01 |
| 17:0 | 1.51b | 1.75a | 1.72a | 0.03 | < 0.01 |
| 18:0 | 12.41b | 14.15a | 14.13a | 0.25 | < 0.01 |
| 18:1 trans-9 | 0.32b | 0.63a | 0.61a | 0.04 | < 0.01 |
| 18:1 trans-11 | 1.13 | 1.05 | 1.08 | 0.07 | 0.73 |
| 18:1 cis-9 | 42.23a | 40.61b | 40.46b | 0.33 | < 0.01 |
| 18:1 cis-11 | 1.91a | 1.70b | 1.70b | 0.03 | < 0.01 |
| 18:2n-6 cis | 2.59b | 3.02a | 3.04a | 0.08 | < 0.01 |
| 18:2n-6 trans | 0.01b | 0.02a | 0.02a | < 0.01 | < 0.01 |
| 18:3n-3 | 0.28 | 0.22 | 0.21 | 0.02 | 0.09 |
| 18:3n-6 cis | 0.02a | 0.01b | 0.01b | < 0.01 | < 0.01 |
| 20:0 | 2.59b | 3.02a | 3.04a | 0.08 | < 0.01 |
| 20:1 | 0.23a | 0.21b | 0.21b | < 0.01 | < 0.01 |
| 20:2 | 0.03b | 0.04a | 0.04a | < 0.01 | < 0.01 |
| 20:3n-3 | 0.02a | 0.01b | 0.01b | < 0.01 | 0.06 |
| 20:3n-6 | 0.16a | 0.12a | 0.12a | < 0.01 | < 0.01 |
| 20:4n-6 | 0.35a | 0.25b | 0.24b | 0.02 | < 0.01 |
| 20:5n3 EPA | 0.04a | 0.01b | 0.01b | < 0.01 | < 0.01 |
| 21:0 | 0.03b | 0.04a | 0.04a | < 0.01 | < 0.01 |
| 22:0 | 0.02 | 0.02 | 0.02 | < 0.01 | 0.99 |
| 22:1n-9 | 0.01 | 0.01 | 0.01 | < 0.01 | 0.15 |
| 22:2 | 0.01 | 0.01 | 0.01 | < 0.01 | 0.40 |
| 22:5n3 DPA | 0.12a | 0.07b | 0.07b | < 0.01 | < 0.01 |
| 22:6n3 DHA | 0.012a | 0.007b | 0.005b | < 0.01 | < 0.01 |
| 23:0 | 0.014a | 0.012b | 0.012b | < 0.01 | 0.01 |
| 24:0 | 0.020 | 0.02 | 0.02 | < 0.01 | 0.26 |
| 24:1 | 0.01 | 0.01 | 0.01 | < 0.01 | 0.91 |
| CLA cis-9, trans-11 | 0.47 | 0.47 | 0.46 | 0.01 | 0.69 |
| CLA trans 10, cis-12 | 0.03b | 0.06a | 0.05a | < 0.01 | < 0.01 |
| CLA cis-9, cis-11 | 0.024a | 0.02ab | 0.01b | < 0.01 | 0.08 |
| CLA trans-9, trans-11 | 0.13b | 0.15a | 0.15a | < 0.01 | 0.01 |
| Total SFA2 | 43.96b | 46.43a | 46.49a | 0.37 | < 0.01 |
| Total MUFA3 | 51.71a | 49.04b | 49.01b | 0.38 | < 0.01 |
| Total PUFA4 | 4.32 | 4.52 | 4.49 | 0.08 | 0.17 |
| Total n-65 | 3.14b | 3.47ab | 3.44a | 0.10 | 0.07 |
| Total n-36 | 0.46a | 0.33b | 0.32b | 0.03 | 0.01 |
| n6-n3 ratio7 | 7.84a | 10.34b | 10.90b | 0.49 | < 0.01 |
| Total FA8 | 14.66b | 17.48a | 18.26a | 0.70 | < 0.01 |
a,bLeast squares means in the same row lacking a common superscript differ (P < 0.05).
1Greatest standard error of the mean among treatments.
2Total SFA = 8:0 + 10:0 + 11:0 + 12:0 + 14:0 + 15:0 + 16:0 + 17:0 + 18:0 + 20:0 + 21:0 + 22:0 + 23:0 + 24:0.
3Total MUFA = 14:1 + 15:1 + 16:1 + 18:1 cis-9 + 18:1 cis-11 + 18:1 trans-9 + 18:1 cis-11 + 20:1 + 24:1.
4Total PUFA = 18:2n-6 cis + 18:2n-6 trans + 18:3n-6 cis + 18:3n-3 + 20:2 + 20:3n-6 + 20:4n-6 and 22:1n-9 + 20:5n-3 + 22:5n-3 + 22:6n-3 + 22:2 + CLA cis-9, trans-11 + CLA trans-10, cis-12 + CLA trans-9, trans-11 + CLA cis-9, cis-11.
5Total n-6 = 18:2n-6 cis + 18:2n-6 trans + 18:3n-6 cis + 20:3n-6 + 20:4n-6.
6Total n-3 = 18:3n-3 + 20:3n-3 + 20:5n-3 + 22:5n-3 + 22:6n-3.
7n-6-n-3: (18:2n-6 cis + 18:2n-6 trans + 18:3n-6 cis + 20:3n-6 + 20:4n-6)/(18:3n-3 + 20:3n-3 + 20:5n-3 + 22:5n-3 + 22:6n-3).
8Total percent of fatty acid in sample.
Monounsaturated fatty acids.
It is well documented that longissimus steaks grain-finished cattle contain a greater amount of total monounsaturated fatty acids (MUFA; Realini et al., 2004; Duckett et al., 2013). However, in the current study, ground beef from grass-fed cattle had higher MUFA (P < 0.01) than the grain-fed treatments. O’Quinn et al. (2016) found strip steaks from grain-finished cattle contained similar total MUFA than organic grass-fed beef. Additionally, oleic acid (18:1 cis-9) and palmitoleic acid (16:1) represented the 2 major MUFA in samples across all treatments and were found in higher (P < 0.01) proportion in grass-fed ground beef than the grain-fed treatments. Enser et al. (1998) reported oleic acid increased in 4 different muscles from grass-fed cattle compared to grain-fed. The higher proportion of MUFA in samples from grass-fed than grain-fed ground beef may be due to various reasons: (1) In the United States, approximately 283 million pounds of meat from cull beef and dairy cows were produced in 2015, yet only 20% was labeled as grass-fed beef, leaving 227 million pounds of domestic unlabeled grass-fed trim in the market. Grass-fed trim could be affecting the fatty acid profile of samples (Cheung and McMahon, 2017). (2) Seasonality plays a key role in fatty acid deposition in cattle, and since the grass-fed ground beef chubs were frozen, animals may have been harvested at different times. Alfaia et al. (2007) reported higher relative proportions for MUFA in longissimus muscle from cattle harvested in spring than autumn.
Polyunsaturated fatty acids.
Total PUFA was similar (P > 0.05) across all treatments. Linoleic acid (18:2n-6 cis), an essential FA in human nutrition, cannot be synthesized by humans (Daley et al., 2010) and it is found in all beef, but typically higher in grass-fed beef (Realini et al., 2004). However, in this experiment, ground beef from grain-fed treatments contained a higher (P < 0.05) proportion for 18:2n-6 cis than grass-fed ground beef. Additionally, some authors reported no significant differences between concentrate (grain) and forage (grass) treatments for 18:2n-6 (Alfaia et al., 2009; Duckett et al., 2013). EPA (20:5n3) and DHA (22:6n3) were higher (P < 0.01) in grass-fed beef than commodity and Angus beef. As expected, omega-3 polyunsaturated fatty acids (n-3 PUFA) were found in the greatest (P < 0.05) proportions in samples of grass-fed beef. The omega-6: omega-3 ratio for grass-fed ground beef was lower (P < 0.05) than grain-fed source; however, the values from all treatments, exceeded the recommended ratio (4:1) to help decrease unfavorable health conditions (Simopoulos, 2002). Overall, the variation in the fatty acid profile from this study may be due to the lack of feeding regimen control, variation of seasonality, variation between muscles, inclusion of cull cow trim and external fat, and labeling restrictions.
Correlations
Pearson correlations between proximate data and consumer palatability ratings are shown in Table 6. Moisture content was negatively correlated with fat content (r = 0.99; P < 0.01). This response has been previously reported when comparing moisture and fat content in various beef muscles (Legako et al., 2015). A correlation between consumer palatability ratings and fat content was not found (P > 0.05). Thus, in our study, fat content alone did not drive the observed consumer responses. Rather, different fatty acid composition due to the finishing diet may have led consumers to prefer grain-fed over grass-fed beef. Overall liking was positively correlated with juiciness, tenderness, flavor liking, and texture liking (P < 0.05). This can be expected and occurred potentially due to the limited ability of consumers to discern between palatability attributes. Several SFA (8:0, 10:0, 14:0, 16:0, 18:0, and total SFA) were correlated (r > 0.43) with texture and overall liking (P < 0.01; Table 7). Furthermore, overall liking was correlated (r > 0.38) with MUFA (18:1 trans-11, 18:1 cis-9, and total MUFA; P < 0.05). In the current study, oleic acid (18:1 cis-9) represented more than one-third of the total fatty acid content of ground beef across all treatments and is known to have the most beneficial effect on beef flavor desirability (Dryden and Marchello, 1970; Westerling and Hedrick, 1979). Texture liking and overall liking were negatively correlated (r– 0.36) with PUFA (18:2n-6 trans, 18:3n-6 cis, 20:2, 20:3n-3, 22:2, 22:6n-3, CLA trans 10, cis-12, CLA cis-9, cis-11, and total PUFA; P < 0.05). These findings are in line with other studies, where PUFAs in ground beef has been identified to be less desirable (Hunt et al., 2016; O’Quinn et al., 2016). In the present study, several PUFA were shown to be negatively correlated with overall liking. Baublits et al. (2009) reported that a higher proportion of PUFA may negatively affect beef fat sensory characteristics. In previous studies, it has been demonstrated that beef from grass-fed cattle has a higher proportion of omega-3 fatty acids in comparison with beef from grain-fed cattle (Daley et al., 2010). As a result of this increase in omega-3, ground beef from grass-fed cattle has been described as “grassy” and “fishy” (Melton et al., 1982b)
Pearson correlation coefficients showing relationships between consumer palatability ratings1 and proximate data2 in Angus, commodity, and grass-fed ground beef
| Item | Overall liking | Tenderness | Juiciness | Flavor liking | Texture liking | Fat | Moisture | Protein |
| Tenderness | 0.68* | |||||||
| Juiciness | 0.70* | 0.84** | ||||||
| Flavor liking | 0.77* | 0.28 | 0.26 | |||||
| Texture liking | 0.90** | 0.67* | 0.74* | 0.59 | ||||
| Fat | 0.38 | –0.12 | 0.23 | 0.30 | 0.29 | |||
| Moisture | –0.26 | 0.21 | –0.28 | –0.38 | –0.34 | –0.99*** | ||
| Protein | –0.46 | 0.07 | 0.11 | –0.68* | –0.18 | –0.41 | 0.39 |
*Significant correlation P < 0.05.
**Significant correlation P < 0.01.
***Significant correlation P < 0.001.
1Consumer rated each steak on a line scale for tenderness, juiciness, flavor liking, texture liking, and overall liking.
2Chemical percentages of fat, moisture, and protein.
Pearson correlation coefficients showing relationships between fatty acids1 and consumer palatability ratings2 in Angus, commodity, and grass-fed ground beef
| Fatty acid | Tenderness | Juiciness | Flavor liking | Texture liking | Overall liking |
| 8:0 | 0.04 | 0.33* | –0.13 | 0.44** | 0.51*** |
| 10:0 | –0.10 | 0.34* | –0.25 | 0.43** | 0.46** |
| 12:0 | 0.17 | 0.35* | –0.24 | 0.45** | 0.46** |
| 14:0 | 0.05 | 0.32* | –0.26 | 0.45** | 0.46** |
| 14:1 | –0.02 | –0.34* | 0.26 | –0.45** | –0.47** |
| 15:0 | 0.38* | –0.26 | 0.29 | –0.45** | –0.44** |
| 15:1 | 0.37* | –0.31* | 0.27 | –0.44** | –0.44** |
| 16:0 | –0.21 | 0.32* | –0.26 | 0.45** | 0.45** |
| 16:1 | 0.01 | –0.33* | 0.26 | –0.45** | –0.46** |
| 17:0 | 0.42* | –0.28 | 0.28 | –0.44** | –0.44** |
| 18:0 | –0.01 | 0.34* | –0.27 | 0.47** | 0.46** |
| 18:1 trans-9 | 0.50** | –0.33* | 0.25 | –0.44** | –0.46** |
| 18:1 trans-11 | 0.07 | 0.34* | –0.22 | 0.43** | 0.44** |
| 18:1 cis-9 | –0.17 | 0.31* | –0.26 | 0.43** | 0.46** |
| 18:1 cis-11 | 0.19 | –0.32* | 0.26 | –0.44** | –0.46** |
| 18:2n-6 cis | 0.31 | 0.35* | –0.24 | 0.45** | 0.47** |
| 18:2n-6 trans | 0.39* | –0.31* | 0.27 | –0.44** | –0.45** |
| 18:3n-3 | 0.07 | 0.29 | –0.25 | 0.41** | 0.45** |
| 18:3n-6 cis | –0.24 | –0.34* | 0.22 | –0.45** | –0.47** |
| 20:0 | –0.01 | –0.35* | 0.24 | –0.41** | –0.46** |
| 20:1 | 0.10 | –0.06 | 0.06 | –0.24 | –0.11 |
| 20:2 | 0.12 | –0.32* | 0.24 | –0.45** | –0.45** |
| 20:3n-3 | –0.13 | –0.34* | 0.25 | –0.41** | –0.46** |
| 20:3n-6 | 0.20 | 0.35* | –0.22 | 0.43** | 0.48** |
| 20:4n-6 | 0.34 | 0.39* | –0.15 | 0.41** | 0.51*** |
| 20:5n3 EPA | 0.19 | 0.36* | –0.16 | 0.23 | 0.45** |
| 21:0 | 0.52** | 0.43** | 0.01 | 0.31* | 0.49** |
| 22:0 | 0.22 | –0.18 | 0.22 | –0.29 | –0.28 |
| 22:1n-9 | –0.04 | –0.18 | 0.24 | –0.39** | –0.20 |
| 22:2 | 0.01 | –0.23 | 0.28 | –0.36* | –0.36* |
| 22:5n3 DPA | 0.32 | 0.38* | –0.16 | 0.37* | 0.52*** |
| 22:6n3 DHA | 0.17 | –0.23 | 0.26 | –0.41** | –0.36* |
| 23:0 | 0.35 | –0.29 | 0.28 | –0.38* | –0.42** |
| 24:0 | 0.28 | –0.01 | 0.23 | –0.29 | –0.12 |
| 24:1 | 0.21 | –0.12 | 0.36* | –0.41** | –0.28 |
| CLA cis-9, trans-11 | 0.34 | 0.34* | –0.17 | 0.46** | 0.54*** |
| CLA trans 10, cis-12 | 0.48** | –0.30* | 0.24 | –0.43** | –0.43** |
| CLA cis-9, cis-11 | 0.13 | –0.32* | 0.25 | –0.45** | –0.38* |
| CLA trans-9, trans-11 | 0.43* | 0.36* | –0.21 | 0.45** | 0.50*** |
| Total SFA | –0.01 | 0.32* | –0.27 | 0.46** | 0.45** |
| Total MUFA | –0.05 | 0.20 | –0.23 | 0.28 | 0.38* |
| Total PUFA | 0.41* | –0.32* | 0.26 | –0.44** | –0.45** |
| Total n-6 | 0.33 | 0.36* | –0.23 | 0.44** | 0.48** |
| Total n-3 | 0.18 | 0.31* | –0.23 | 0.39* | 0.47** |
| n6-n3 ratio | 0.03 | 0.36* | –0.24 | 0.50*** | 0.45** |
| Total FA3 | –0.31 | –0.27 | 0.26 | –0.40** | –0.43** |
*Significant correlation P < 0.05.
**Significant correlation P < 0.01.
***Significant correlation P < 0.001.
1Chemical percentages of fatty acids based on total fatty acids.
2Consumer rated each steak on a continuous line scale for tenderness, juiciness, flavor liking, texture liking, and overall liking.
3Total percent of fatty acid in sample.
Conclusion
Consumers preferred Angus and commodity beef over grass-fed beef. Different fatty acid composition can play a determinant factor in palatability and can affect consumer eating experience. The proportion of PUFA from commodity and Angus ground beef and grass-fed ground beef was similar in this study. Individual PUFA, including EPA (20:5n3) and DHA (22:6n3) were in greater proportion in grass-fed than grain-fed ground beef. Grass-fed labels can influence purchasing decision of ground beef and it was observed that 80% of panelists, who participated in this study, were willing to spend extra ($0.86 ± $0.49) to purchase omega-3 rich ground beef products.
Notes
- This is contribution no. 19-239-J of the Kansas Agricultural Experiment Station. [^]
Literature Cited
Alfaia, C. P.Alves, S. P.Martins, S. I.Costa, A. S.Fontes, C. M.Lemos, J. P.Bessa, R. J.Prates, J. A.. 2009. Effect of the feeding system on intramuscular fatty acids and conjugated linoleic acid isomers of beef cattle, with emphasis on their nutritional value and discriminatory ability. Food Chem. 114:939–946. doi:10.1016/j.foodchem.2008.10.041http://dx.doi.org/10.1016/j.foodchem.2008.10.041http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=Agronomy_sub&KeyUT=WOS:000264258800025&DestLinkType=FullRecord&DestApp=WOS_CPL&UsrCustomerID=9992b2403adf8c36119d0b6fce39b97c
Alfaia, C. P.Castro, M. L.Martins, S. I.Portugal, A. P.Alves, S. P.Fontes, C. M.Bessa, R.J.Prates, J. A.. 2007. Influence of slaughter season and muscle type on fatty acid composition, conjugated linoleic acid isomeric distribution and nutritional quality of intramuscular fat in Arouquesa-PDO veal. Meat Sci. 76:787–795. doi:10.1016/j.meatsci.2007.02.023http://dx.doi.org/10.1016/j.meatsci.2007.02.023http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=Agronomy_sub&KeyUT=WOS:000246823700027&DestLinkType=FullRecord&DestApp=WOS_CPL&UsrCustomerID=9992b2403adf8c36119d0b6fce39b97c
American Grassfed Association (AGA). 2018. Grassfed ruminant standards. (accessed 10 Mar. 2019)https://www.americangrassfed.org/wp-content/uploads/2017/08/AGA-Grassfed-Ruminant-Standards-2018-1.pdf.
American Meat Science Association (AMSA). 2016. Research guidelines for cookery, sensory evaluation, and instrumental tenderness measurements of meat . 2nd ed. American Meat Science Association, Champaign, IL.
Baublits, R. T.Pohlman, F. W.Brown, A. H.Johnson, Z. B.Rule, D. C.Onks, D. O.Murrieta, C. M.Richards, C. J.Sandelin, B. A.Loveday, H. D.Pugh, R. B.. 2009. Correlations and prediction equations for fatty acids and sensory characteristics of beef longissimus rib steaks from forage‐fed cattle and retail USDA Choice and Select rib steaks. J. Muscle Foods 20(1):1–17. doi:10.1111/j.1745-4573.2008.00129.xhttp://dx.doi.org/10.1111/j.1745-4573.2008.00129.xhttp://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=Agronomy_sub&KeyUT=WOS:000262054000001&DestLinkType=FullRecord&DestApp=WOS_CPL&UsrCustomerID=9992b2403adf8c36119d0b6fce39b97c
Cheung, R.McMahon, P.. 2017. Back to grass: The market potential for US grassfed beef. (accessed 1 Aug. 2018.)http://www.stonebarnscenter.org/images/content/3/9/39629/Grassfed-Market Study-F.pdf.
Crouse, J. D.Cross, H. R.Seideman, S. C.. 1984. Effects of a grass or grain diet on the quality of three beef muscles. J. Anim. Sci. 58:619–625. doi:10.2527/jas1984.583619xhttp://dx.doi.org/10.2527/jas1984.583619x
Daley, C. A.Abbott, A.Doyle, P. S.Nader, G. A.Larson, S.. 2010. A review of fatty acid profiles and antioxidant content in grass-fed and grain-fed beef. Nutr. J. 9(1):10. doi:10.1186/1475-2891-9-10http://dx.doi.org/10.1186/1475-2891-9-10
Dryden, F. D.Marchello, J. A.. 1970. Influence of total lipid and fatty acid composition upon the palatability of three bovine muscles. J. Anim. Sci. 31:36–41. doi:10.2527/jas1970.31136xhttp://dx.doi.org/10.2527/jas1970.31136x
Duckett, S. K.Neel, J. P. S.Lewis, R. M.Fontenot, J. P.Clapham, W. M.. 2013. Effects of forage species or concentrate finishing on animal performance, carcass and meat quality. J. Anim. Sci. 91:1454–1467. doi:10.2527/jas.2012-5914http://dx.doi.org/10.2527/jas.2012-5914http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=Agronomy_sub&KeyUT=WOS:000319691500045&DestLinkType=FullRecord&DestApp=WOS_CPL&UsrCustomerID=9992b2403adf8c36119d0b6fce39b97c
Enser, M.Hallett, K. G.Hewett, B.Fursey, G. A. J.Wood, J. D.Harrington, G.. 1998. Fatty acid content and composition of UK beef and lamb muscle in relation to production system and implications for human nutrition. Meat Sci. 49:329–341. doi:10.1016/S0309-1740(97)00144-7http://dx.doi.org/10.1016/S0309-1740(97)00144-7
Griffin, D. B.Savell, J. W.. 2018. Understanding USDA beef quality grades. (accessed 1Aug. 2019)https://meat.tamu.edu/files/2018/10/Understanding-USDA-beef-quality-grades.pdf.
Hedrick, H. B.Paterson, J. A.Matches, A. G.Thomas, J. D.Morrow, R. E.Stringer, W. G.Lipsey, R. J.. 1983. Carcass and palatability characteristics of beef produced on pasture, corn silage and corn grain. J. Anim. Sci. 57:791–801. doi:10.2527/jas1983.574791xhttp://dx.doi.org/10.2527/jas1983.574791x
Howe, J. C.Trainer, D.Holden, J. M.Douglass, L. W.. 2007. Fat content of ground beef: Comparison of actual (analytical) to label claim. Fed. Am. Soc.Exp. Biol. 21.
Hunt, M. R.Legako, J. F.Dinh, T. T. N.Garmyn, A. J.O’Quinn, T. G.Corbin, C. H.Rathman, R. J.Brooks, J. C.Miller, M. F.. 2016. Assessment of volatile compounds, neutral and polar lipid fatty acids of four beef muscles from USDA Choice and Select graded carcasses and their relationships with consumer palatability scores and intramuscular fat content. Meat Sci. 116:91–101. doi:10.1016/j.meatsci.2016.02.010http://dx.doi.org/10.1016/j.meatsci.2016.02.010http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=Agronomy_sub&KeyUT=WOS:000372942500012&DestLinkType=FullRecord&DestApp=WOS_CPL&UsrCustomerID=9992b2403adf8c36119d0b6fce39b97c
Kerth, C. R.Braden, K. W.Cox, R.Kerth, L. K.Rankins, D. L.. 2007. Carcass, sensory, fat color, and consumer acceptance characteristics of Angus-cross steers finished on ryegrass (Lolium multiflorum) forage or on a high-concentrate diet. Meat Sci. 75:324–331. doi:10.1016/j.meatsci.2006.07.019http://dx.doi.org/10.1016/j.meatsci.2006.07.019http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=Agronomy_sub&KeyUT=WOS:000242776500017&DestLinkType=FullRecord&DestApp=WOS_CPL&UsrCustomerID=9992b2403adf8c36119d0b6fce39b97c
Killinger, K. M.Calkins, C. R.Umberger, W. J.Feuz, D. M.Eskridge, K. M.. 2004. A comparison of consumer sensory acceptance and value of domestic beef steaks and steaks from a branded, Argentine beef program. J. Anim. Sci. 82:3302–3307. doi:10.2527/2004.82113302xhttp://dx.doi.org/10.2527/2004.82113302x
Legako, J. F.Brooks, J. C.O’Quinn, T. G.Hagan, T. D. J.Polkinghorne, R.Farmer, L. J.Miller, M. F.. 2015. Consumer palatability scores and volatile beef flavor compounds of five USDA quality grades and four muscles. Meat Sci. 100:291–300. doi:10.1016/j.meatsci.2014.10.026http://dx.doi.org/10.1016/j.meatsci.2014.10.026http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=Agronomy_sub&KeyUT=WOS:000347765700041&DestLinkType=FullRecord&DestApp=WOS_CPL&UsrCustomerID=9992b2403adf8c36119d0b6fce39b97c
Mandell, I. B.Buchanan-Smith, J. G.Campbell, C. P.. 1998. Effects of forage vs grain feeding on carcass characteristics, fatty acid composition, and beef quality in Limousin-cross steers when time on feed is controlled. J. Anim. Sci. 76:2619–2630. doi:10.2527/1998.76102619xhttp://dx.doi.org/10.2527/1998.76102619x
Melton, S. L.Amiri, M.Davis, G. W.Backus, W. R.. 1982a. Flavor and chemical characteristics of ground beef from grass-, forage-grain-and grain-finished steers. J. Anim. Sci. 55:77–87. doi:10.2527/jas1982.55177x
Melton, S. L.Black, J. M.Davis, G. W.Backus, W. R.. 1982b. Flavor and selected chemical components of ground beef from steers backgrounded on pasture and fed corn up to 140 days. J. Food Sci. 47:699–704. doi:10.1111/j.1365-2621.1982.tb12694.x
Melton, S. L. 1990. Effects of feeds on flavor of red meat: A review. J. Anim. Sci. 68:4421–4435. doi:10.2527/1990.68124421xhttp://dx.doi.org/10.2527/1990.68124421x
O’Quinn, T. G.Woerner, D. R.Engle, T. E.Chapman, P. L.Legako, J. F.Brooks, J. C.Belk, K. E.Tatum, J. D.. 2016. Identifying consumer preferences for specific beef flavor characteristics in relation to cattle production and postmortem processing parameters. Meat Sci. 112:90–102. doi:10.1016/j.meatsci.2015.11.001http://dx.doi.org/10.1016/j.meatsci.2015.11.001http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=Agronomy_sub&KeyUT=WOS:000366782100015&DestLinkType=FullRecord&DestApp=WOS_CPL&UsrCustomerID=9992b2403adf8c36119d0b6fce39b97c
Realini, C. E.Duckett, S. K.Brito, G. W.Dalla Rizza, M.De Mattos, D.. 2004. Effect of pasture vs. concentrate feeding with or without antioxidants on carcass characteristics, fatty acid composition, and quality of Uruguayan beef. Meat Sci. 66:567–577. doi:10.1016/S0309-1740(03)00160-8http://dx.doi.org/10.1016/S0309-1740(03)00160-8
Rouquette, F. M.Forbes, T. D. A.Miller, R. K.Hawks, K. R.Santos, C. C.Delgado, E. F.Holloway, J. W.Warrington, B. G.Long, C. R.. 2014. Natural beef production and growth of Bonsmara steers stocked on rye and ryegrass pastures at humid and semiarid environments. Prof. Anim. Sci. 30:285–295. doi:10.15232/S1080-7446(15)30119-4http://dx.doi.org/10.15232/S1080-7446(15)30119-4
Simopoulos, A. P. 2002. The importance of the ratio of omega-6/omega-3 essential fatty acids. Biomed. Pharmacother. 56:365–379. doi:10.1016/S0753-3322(02)00253-6http://dx.doi.org/10.1016/S0753-3322(02)00253-6
Smith, S. 2013. Grass-fed vs grain- fed ground beef. No difference in healthfulness. (accessed 10 July 2018)http://animalscience.tamu.edu/2013/12/07/ground-beef-from-grass-fed-and-grain-fed-cattle-does-it-matter/.
Sukhija, P. S.Palmquist, D. L.. 1988. Rapid method for determination of total fatty acid content and composition of feedstuffs and feces. J. Agric. Food Chem. 36:1202–1206. doi:10.1021/jf00084a019http://dx.doi.org/10.1021/jf00084a019
Troutt, E. S.Hunt, M. C.Johnson, D. E.Claus, J. R.Kastner, C. L.Kropf, D. H.Stroda, S.. 1992. Chemical, physical, and sensory characterization of ground beef containing 5 to 30 percent fat. J. Food Sci. 57:25–29. doi:10.1111/j.1365-2621.1992.tb05416.xhttp://dx.doi.org/10.1111/j.1365-2621.1992.tb05416.x
United States Department of Agriculture, Agricultural Marketing Service (USDA-AMS). 2007. United States standards for livestock and meat marketing claims, grass (forage) fed claim for ruminant livestock and the meat products derived from such livestock. Fed. Regist. 72:58631–58637.
United States Department of Agriculture, Agricultural Marketing Service (USDA-AMS). 2018. National monthly grass fed beef report, livestock, poultry and grain market news. (accessed 10 Feb. 2019)https://www.ams.usda.gov/mnreports/lsmngfbeef.pdf.
Von Seggern, D. D.Calkins, C. R.Johnson, D. D.Brickler, J. E.Gwartney, B. L.. 2005. Muscle profiling: Characterizing the muscles of the beef chuck and round. Meat Sci. 71:39–51. doi:10.1016/j.meatsci.2005.04.010http://dx.doi.org/10.1016/j.meatsci.2005.04.010
Westerling, D. B.Hedrick, H. B.. 1979. Fatty acid composition of bovine lipids as influenced by diet, sex and anatomical location and relationship to sensory characteristics. J. Anim. Sci. 48:1343–1348. doi:10.2527/jas1979.4861343xhttp://dx.doi.org/10.2527/jas1979.4861343x
Wood, J. D.Richardson, R. I.Nute, G. R.Fisher, A. V.Campo, M. M.Kasapidou, E.Sheard, P. R.Enser, M.. 2003. Review Effects of fatty acids on meat quality. Meat Sci. 66:21–32. doi:10.1016/S0309-1740(03)00022-6
Wulf, D. M.O’Connor, S. F.Tatum, J. D.Smith, G. C.. 1997. Using objective measures of muscle color to predict beef longissimus tenderness. J. Anim. Sci. 75:684–692. doi:10.2527/1997.753684xhttp://dx.doi.org/10.2527/1997.753684x