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PROCESSING, PRODUCTS, AND FOOD SAFETY |
* Department of Animal Science, Iowa State University, Ames 50011
2 Corresponding author: sebranek{at}iastate.edu
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONREFERENCES |
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Key Words: broiler • organic • free-range • meat quality • sensory analysis
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONREFERENCES |
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Organic poultry production, according to guidelines of USDA Food Safety and Inspection Service, must utilize organic feed, omit antibiotics, provide access to the outdoors, and produce the birds on premises that are certified as organic by the USDA (Winter and Davis, 2006). Free-range poultry production requires outdoor access but is not as limited as organic production with regard to the use of production inputs and guidelines such as feed, antibiotic use, and premise certification (FSIS, 2006).
Consumer purchases of poultry products are determined by many factors including wholesomeness, quality, class, nutritive value, cost, and informative labeling (AMS-USDA, 1995). Because of the obvious consumer interest in organic and free-range broilers, the present study was designed to compare characteristics of meat from organic, free-range, and conventionally raised broilers as currently available to consumers in the marketplace. Because genotypes of organic, free-range, and conventional broilers may be similar (Fanatico et al., 2005b), the production environment is likely to be an important contributor to any significant differences that may exist between these broiler types. Castellini et al. (2002) found when comparing organically raised chickens to conventional that organic chickens had less fat. These authors attributed this difference to increased physical activity by the organically produced chickens that favored myogenesis over lipogenesis. Kishowar et al. (2005) concluded that, for breast meat from organic, free-range, and corn-fed chickens, the appearance and texture of the meat were the attributes that were most distinguishable between groups. Only a subgroup of sensory panelists in that study could distinguish differences in aroma and flavor.
There are a limited number of studies that have compared organic, free-range or conventional broiler meat quality (Castellini et al., 2002; Fanatico et al., 2005a,b, 2006; Kishowar et al., 2005). However, these studies did not assess meat quality characteristics representative of retail broilers from commercial organic, free-range, and conventional poultry production systems as currently marketed to US consumers. Consequently the objective of this study was to assess meat quality and quantity from organic, free-range, and conventionally raised broiler chickens as they are currently presented to consumers in retail markets to provide objective value comparisons in the same context as consumer purchases. The large price variations paid by consumers for meat from organic, free-range, and conventional broilers warrants a study of the chemical, physical, and sensory properties of the aforementioned chicken meat sources. Although genetics, production methods, and season have been shown to influence meat quality of broilers (Bianchi et al., 2007; Fanatico et al., 2007; Ponte et al., 2008), this study is not a comparison of broiler production systems or genetics but rather a survey of broilers in retail markets as they are currently available to consumers.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONREFERENCES |
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Measurements and Evaluations
Raw chickens were evaluated for color, pH, carcass component yield, degree of oxidation, proximate analysis, and fatty acid analysis, as detailed in the following description of methods. Cooked chickens were evaluated for color, carcass component yield, degree of oxidation, proximate analysis, cooking yield, and shear force tenderness values.
Carcass Component Yield
Weight yields of carcass components (light meat, dark meat, skin, and bones) were measured on raw and cooked broilers by weighing the entire chicken, then physically separating the light meat, dark meat, skin, and bones and weighing each of the 4 components. Four broilers from each supplier were utilized for these measurements of raw meat yields, and 4 were utilized for cooked meat yields.
Cooking Yield
Cooking yield was determined by weighing 4 whole broilers from each supplier before and after cooking. Chickens were cooked in an Alkar (Lodi, WI) thermal processing oven at 82°C with steam (100% relative humidity) to an internal temperature of 72°C. Samples used for measurement of cooking yield were independent of those used for sensory analysis.
Proximate Analysis
Fat, moisture, and protein content of raw and cooked breasts, thighs, and skin were each independently measured in duplicate from each of 4 raw broilers and 4 cooked broilers from each supplier. Samples for proximate analysis were frozen until analyzed at the Iowa State University Chemistry Laboratory. Fat, moisture, and protein content was measured following AOAC methodology (AOAC, 1995).
Color
Color (lightness, L*; redness, a*; yellowness, b*) was measured in triplicate on raw and cooked breast meat, thigh meat, and skin of 4 raw and 4 cooked chickens from each supplier using a hand-held HunterLab Color Difference Meter (Hunter Associates Laboratory, Reston, VA). Standard calibration with black and white tiles was used before measurements. A D65 midday daylight light source and 10° observer setting was used for all measurements.
pH
The pH was measured on whole intact raw breast (pectoralis major) and thigh muscles (quadriceps femoris) of 4 chickens from each supplier. Measurement of pH was performed using a Hanna (model HI99161) digital pH meter equipped with a Hanna (model FC202D) electrode (Hanna Instruments Inc., Highland Industrial Park, Woonsocket, RI) calibrated before measurement with pH 4.0 and 7.0 buffer solutions from Fisher Scientific (Waltham, MA).
Thiobarbituric Acid Reactive Substances Analysis
Thiobarbituric acid reactive substances (TBARS) values were measured to assess lipid oxidation on duplicate samples of 4 raw and 4 cooked breasts and thighs from different broilers from each supplier. The TBARS values were measured on raw products after allowing the products to thaw for 48 h. Ten grams of homogenized minced muscle was added to 95.7 mL of distilled water and 2.5 mL of 4 N HCl in a round-bottom flask. The mixture was distilled until 50 mL of distillate was obtained. Five milliliters of the distillate and 5 mL of thiobarbituric acid reagent (15% trichloroacetic acid, 0.375% thiobarbituric acid) were heated in a water bath at 100°C for 35 min. After cooling at room temperature for 30 min, the absorbance was measured at 538 nm against an appropriate blank. The TBARS values were obtained by multiplying optical density by 7.8 (Konieko, 1985). Oxidation products were quantified as malonaldehyde equivalents (mg of malonaldehyde/kg of muscle).
Fatty Acid Profiles
Fatty acid profiles were measured on raw skinless breast and thigh muscles using gas chromatography (GC). One sample of homogenized minced muscle from each of 4 breasts and thighs from each supplier was measured. For this measurement, 1 mL of methylating reagent (boron trifluoride-methanol) was added to a test tube containing the total lipid extracted from breast or thigh meat, following methodology of Du et al. (2000), and incubated in a water bath at 90°C for 50 min. After cooling to room temperature, 2 mL of hexane and 5 mL of water were added, mixed thoroughly, and left at room temperature overnight for phase separation. The top hexane layer containing methylated fatty acids was used for GC analysis (Chin et al., 1992). Analysis of fatty acid composition was performed with a GC (Hewlett-Packard 6890) equipped with an autosample injector and flame ionization detector. A capillary column (SUPERCOWAX –10, 30 m x 0.25 mm x 0.25 µm film thickness; Supelco, Bellefonte, PA) was used. Ramped oven temperature conditions (increased from 190 to 200°C at 5°C per min, held for 6 min, then increased to 220°C at 10°C per min, then increased to 230°C at 5°C per min, and held for 8 min) were used. Temperatures of the inlet and detector were 280 and 320°C, respectively. Helium was used as a carrier gas, and a constant column flow of 1.0 mL/min was used. Flame ionization detector air, H2, and make-up gas (He) flows were 350 mL/min, 35 mL/min, and 38.3 mL/ min, respectively. Fatty acids were identified using a mass selective detector (model 5973, Agilent Technologies, Wilmington, DE). The GC-mass selective detector procedure was performed with the same column and oven temperature conditions described previously. The ionization potential of the mass selective detector was 70 eV, and the scan range was 45 to 450 m/z. Identification of fatty acids was achieved by comparing mass spectral data with those of the Wiley library. The fatty acids were reported as percentages of total lipids.
Tenderness
Tenderness was measured on cooked broiler breasts and thighs using a Stable Microsystems TAXT-2 Texture Analyzer (Godalming, UK). Tenderness was measured in duplicate on each sample using a star probe for shear force penetration to 80% of the initial product height. Resistance to shear was measured as kilograms/centimeter2. The location for measurement on breasts and thighs were chosen in an area free from defects and as close to the same location each time as could be determined by visual assessment. Samples used for tenderness measurements were independent of those used for sensory analysis.
Trained Panel Sensory Analysis
Ten panelists were recruited from the faculty, staff, and students of Iowa State University. The University’s Human Subjects in Research Committee approved the project, and the panelists were compensated for their participation. The same panelists served on both the breast and thigh panels. There were two 1-h training sessions each for the thigh samples and for the breast samples. During training, panelists were familiarized with the sensory terms, the tasting techniques, and the computer software scoring system.
The evaluations of breasts and thighs were conducted as separate panels. The cooking procedures were identical for both breasts and thighs, using a George Foreman Indoor/Outdoor Grill (Model GGR62, Lake Forest, IL) to cook samples to an internal temperature of 77°C. The temperature of the samples was monitored using a thermocouple (Chromega/Alomega) attached to an Omega digital thermometer (model DSS-650, Omega Engineering, Stamford, CT). Panelists received product samples as 2 approximately 15 mm x 15 mm pieces immediately following cooking. Four test sessions for thighs and 4 test sessions for breasts were conducted. Each panelist evaluated 6 samples per session (2 from each treatment from different suppliers). Each treatment-supplier combination was evaluated twice over the course of the study but in different sessions. The samples were randomized for cooking and serving and were then presented sequentially in partitioned booths equipped with red florescent lights. Water and unsalted crackers were available to each of the panelists. A line scale with 15 marked numerical units was used with descriptors representing low intensity on the left and high intensity at the right for scoring the following attributes: chicken aroma, tenderness, chewiness, moistness, and chicken flavor. Data was collected using a computerized sensory scoring system (Compusense 5, v4.4, Compusense Inc., Guelph, Ontario, Canada).
Statistical Analysis
The SAS PROC MIXED (version 9.1, SAS Inst. Inc., Cary, NC) was used for statistical analysis. Pairwise treatment differences were determined with the Tukey Kramer adjustment. Significance was determined at P < 0.05. A nested model was used for the sensory data. Both subject and session effects were fitted as random, whereas treatment and supplier effects were fitted as fixed with supplier nested within the treatment.
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RESULTS AND DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONREFERENCES |
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Organic broilers yielded more (P < 0.05) dark meat (23.2%) and less (P < 0.05) skin (12.2%) than free-range (21.5 and 14.4%, respectively) and conventionally raised (21.5 and 13.9%, respectively) broilers on a raw meat basis. There were no differences (P > 0.05) in raw dark meat or skin yields between free-range and conventional, and no differences between organic, free-range, and conventional chickens for light meat and bone yields.
After cooking, organic broilers yielded significantly less (P < 0.05) light meat on a percentage basis compared with free-range and conventional, and more bone (P < 0.05) compared with free-range chickens (Figure 1
). Light meat yields from organically raised birds were less than free-range and conventionally raised birds after cooking by 5.5 and 6.2 percentage points, respectively. The difference in light meat yield after cooking may be partially due to the fat content that was lost during cooking. Fat content, on a raw basis, was highest for organic broilers compared with free-range and conventional. However, after cooking, breasts from the organically raised birds had the lowest fat content relative to free-range and conventionally raised chickens. Cooked carcass light meat yields were not significantly different between free-range and conventional broilers. There were no differences (P > 0.05) between any of the 3 broiler types for raw dark meat or skin yields after cooking.
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Total Cooking Yield
Free-range broilers had 3.19% greater (P < 0.05) whole carcass cooking yield (88.91%) than conventional broilers (85.72%) but were not significantly different (P > 0.05) from organic (86.90%). Cooking yields for organic and conventional broilers were not significantly different from one another. Castellini et al. (2002) concluded that the breast and drumstick cook losses were greater for organic chickens compared with conventional chickens because final muscle pH was lower. The lower muscle pH (pH 5.75 to pH 5.80 for breasts; pH 6.02 to pH 6.10 for thighs) of organic chickens relative to conventional chickens (pH 5.96 to pH 5.98 for breasts; pH 6.18 to pH 6.25 for thighs) in work conducted by Castellini et al. (2002) was closer to the meat isoelectric point (approximately pH 5.2) and therefore is a likely reason for a lower water holding capacity and lower cooking yield. It is well recognized (Castellini et al. (2002) that reduced muscle pH is likely to result in reduced water-binding ability. In the present study, however, this was not observed. The pH (Figure 2) for free-range chickens in our study was the lowest relative to organic and conventional chickens, but resulted in a higher (P < 0.05) cooking yield compared with conventional broilers as noted above. Although the cooking yield trend was opposite of what was expected given each respective muscle pH, the result could be explained by differences in other inherent meat attributes such as protein and moisture content. Consistent with the present work, Qiao et al. (2001) also found that broiler muscle with pH values closer to the isoelectric point had higher water holding capacity. These results also suggest that other factors besides muscle pH affected cooking yield.
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Raw breast meat from organic and free-range broilers was lower (P < 0.05) in moisture content and higher (P < 0.05) in protein content compared with conventional broilers (Table 1). Raw thighs from organic and free-range broilers also had higher (P < 0.05) protein content compared with conventional broilers. Raw skin from organic birds had significantly less fat (P < 0.05), more moisture (P < 0.05), and higher protein content (P < 0.05) than free-range and conventional broilers. Fat, moisture, and protein content of raw skin was not significantly (P > 0.05) different among free-range and conventional broilers (Table 1).
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). Although statistically significant, differences in fat, moisture, and protein content of breast and thigh meat between organic, free-range, and conventional chickens were not large and may or may not be practically important. Raw skin from organic birds had significantly (P < 0.05) lower fat content in comparison to free-range and conventional broilers, which could be important to consumers concerned with fat intake; however, when cooked, no significant differences (P > 0.05) for fat content of the skin was observed.
Many factors affect fat, moisture, and protein content of raw and cooked meat, including feed rations, physical activity, and genetics (Zerehdaran et al., 2004; Cangar et al., 2006; Rizzi et al., 2007). However, in the present study, these factors were unknown because all samples were collected at the retail level.
Muscle pH
Breast meat from organic broilers had a higher pH (P < 0.05) than free-range or conventional broilers, which were not different (P > 0.05) from each other (Figure 2). Thighs from organic broilers also had a higher pH (P < 0.05) compared with free-range but were not different (P > 0.05) from conventional broilers.
In normal antemortem muscle, the pH is approximately 7.2. At the time of slaughter, oxygen and nutrients that are supplied by way of the circulatory system are stopped. Glycogen, which supplies energy to the muscle, is metabolized postmortem in an anaerobic environment to lactic acid, which reduces muscle pH (Nissen and Young, 2006). The rate and the extent of pH decline will have a large influence on meat quality characteristics. Variation in muscle pH is likely to influence color (Govindarajan, 1973) and the ability of meat to hold water. The isoelectric point of meat is a pH of approximately 5.2, at which point meat is recognized as having very poor water holding capacity (Castellini et al., 2002). Generally speaking, higher meat pH is more effective for retaining desirable color and moisture absorption properties.
Color
In the raw product comparisons, breasts and thighs from organic broilers were darker (L*; P < 0.05) and less yellow (b*; P < 0.05) than those from free-range or conventional broilers (Table 2). Breasts and thighs from free-range broilers were less yellow (P < 0.05) than those from conventional chickens. Color measurement of raw breasts, thighs, and skins from organic and free-range also showed less yellow color (P < 0.05) compared with conventional broilers. Cooked free-range breasts and skins (data not shown) were less red (a*; P < 0.05) compared with conventional broiler samples. Even though color values were significantly different when measured instrumentally; in practical terms, the only clear trend observed was for b* values (yellowness) of breasts, thighs, and skin from conventional chickens. The chickens utilized for this study were purchased as whole processed broiler carcasses, and therefore the nutritional and environmental factors that might affect color variation were not known. However, the measured color values in the present study were consistent with past research conducted by Govindarajan (1973) in that darker color values were associated with higher pH values. Gonvindarajan (1973) concluded the darker color resulted from oxygen-consuming mitochondrial enzymes that were more active at higher pH levels. Muscle type could have also dictated the color values. Lonergan et al. (2003) concluded that muscle fiber type, specifically proportions of white and red muscle fibers, could have been the source of variation in unique chicken populations. In our study, raw thighs from free-range birds had higher (P < 0.05) redness values, which could be attributed to increased myoglobin content, and we speculate that this may have occurred from increased physical activity associated with access to the outdoors. Organic chickens also have access to the outdoors; however, raw thigh color values were not different from conventional broilers. The age of the birds could also affect redness values. Older birds typically have higher concentrations of myoglobin compared with younger birds. Castellini et al. (2002) found that organic birds had lower live weights at both 56 and 81 d of age compared with conventional broilers. Organic broilers, therefore, at equivalent slaughter weights would be older at the time of slaughter and theoretically more red in appearance. On the other hand, Remignon et al. (1995) reported that selection for rapid growth in chickens did not alter muscle fiber types. Furthermore, Fanatico et al. (2005b) indicated that US organic and free-range producers utilize fast-growing genotypes similar to genotypes used for conventional production. Consequently, the ages of the broilers at the time of slaughter in this study are probably similar and, if so, would contribute only subtle differences in color.
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Raw breasts and thighs from free-range broilers were significantly lower (P < 0.05) in TBARS values than organic and conventional broilers (Table 3), whereas the TBARS values for raw organic and conventional breasts and thighs did not differ significantly (P < 0.05). The TBARS values for the cooked samples were not significantly different (P < 0.05) in any of the comparisons. These values represent the level of oxidation of lipids and are measures of malonaldehyde, ketones, and similar oxidation products. Even though raw TBARS values were significantly different, in practical terms, the TBARS values were all very low, and no rancid flavors would be detectable. A TBARS value of 1 or less, or approximately 0.8 mg malonaldehyde per kilogram of meat, is not generally considered indicative of perceptible rancidity (O’Neill et al., 1998). The TBARS values for raw and cooked thighs were consistently higher than breast pieces, which could be attributed to the oxidative effects of higher iron content in the thighs compared with breast pieces, although this was not measured in the current study.
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Fatty Acid Profiles
Individual fatty acids were quantified and the values for each combined into appropriate categories for total saturated, monounsaturated, polyunsaturated, n-3, and n-6 fatty acids as shown in Table 4. Organic broilers had less (P < 0.05) saturated and monounsaturated fatty acids, and clearly more (P < 0.05) polyunsaturated, n-3, and n-6 fatty acids compared with free-range and conventional birds. Free-range broilers had more (P < 0.05) saturated and n-3 polyunsaturated fatty acids but less (P < 0.05) monounsaturated fatty acids than conventional broilers. The difference in fatty acid content is likely due to dietary fatty acid intake. It has long been recognized that the composition of dietary fat will affect the composition of fat deposited as carcass fat (Gyles, 1988; Du et al., 2000). Organic poultry production is clearly different from conventional, though diets are likely to be similar to conventional diets, both consisting mainly of corn and soybean meal. Access to grass and other outdoor organic matter may explain the difference between organic and conventional chickens because conventional chickens are confined indoors (Castellini et al., 2002). However, this assumption does not explain the difference between organic and free-range chickens because both have access to the outdoors. More investigation is needed to explain these results.
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Tenderness
Both the breast and thigh meat from conventional broilers was more (P < 0.05) tender, requiring less shear force (2.42 and 1.45 kg/cm2, respectively), than the breasts or thighs from organic (2.70 and 1.88 kg/ cm2, respectively) and free-range birds (3.00 and 1.89 kg/cm2, respectively). Breast meat from free-range birds was least (P < 0.05) tender.
Castellini et al. (2002) found that organic breasts and drumsticks possessed lower shear values when compared with conventionally raised chickens. Farmer et al. (1997), when comparing 2 genotypes of chickens for effects of diets and stocking densities, found that genotype and diet contributed the most to textural attributes, whereas stocking density contributed to a lesser extent. Rizzi et al. (2007) reported that genotype of organic laying hens affected meat texture more than other sensory properties such as odor and flavor. Many factors including diet, age, preslaughter handling, and postslaughter chilling affect meat tenderness, and it is difficult to conclusively assess the role of organic, free-range, and conventional production systems alone on meat tenderness.
Trained Panel Sensory Evaluation
The sensory panel did not detect differences (P > 0.05) between organic, free-range and conventional breasts for chicken aroma, tenderness, chewiness, moistness, or chicken flavor (Table 5). The sensory panel results, however, indicated that conventional chicken thighs (Table 6) were more tender (P < 0.05) and less chewy (P < 0.05) than thighs from organic and free-range birds, results which confirmed the instrumental tenderness values observed. All other sensory attributes for the thighs were not different.
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Retail Price for Organic, Free-Range, and Conventional Whole Broilers
At the time of purchase, March through May of 2006, a wide range in prices was observed. The average (n = 60) price for organic [$3.19/lb ($7.03/kg)] and free-range [$2.78/lb ($6.13/kg)] whole broilers was 247 and 216% greater, respectively, when compared with conventional [$1.29/lb ($2.84/kg)] whole broilers. These prices probably reflect to some degree the price that is required to maintain grower profitability but also reflect consumer perceptions and demand. Organic production clearly requires use of more expensive inputs, such as organic corn and soybeans, in addition to the exclusion of other modern production interventions that aid in growth performance and capitalize on efficiency (Winter and Davis, 2006). Although free-range poultry production may not require the same degree of input costs as organic production, typically it is different from conventional and also commands a higher retail product price. Obviously, organic and free-range prices reflect the premium that consumers are willing to pay for organic and free-range chicken. It is interesting to note that organic and free-range poultry was typically sold frozen, which could be the result of a slower inventory turnover.
The most significant differences observed in this study between broilers currently provided to consumers as organic, free-range, and conventional chickens included color, fatty acid composition, and tenderness. Conventionally raised chickens consistently possessed more (P < 0.05) yellow appearance for breast, thigh, and skin pieces when compared with organic and free-range carcass components. Organic chicken breasts and thighs had significantly greater (P < 0.05) percentages of polyunsaturated fatty acids, including n-3 and n-6 fatty acids compared with free-range and conventional chickens. This may be of particular value to consumers concerned about fat and healthfulness of saturated vs. unsaturated fatty acids. It may also be part of the perceived advantages that result in premium prices for these products. On the other hand, instrumental measurements as well as sensory evaluations found that thighs from conventional broilers were more (P < 0.05) tender when compared with organic and free-range chickens. It should be kept in mind that these results reflect characteristics of these broilers as marketed to consumers and do not necessarily reflect differences in productions systems because production systems, slaughter, and handling were not controlled in this survey. At the same time, these results demonstrate what consumers are experiencing when purchasing broilers marketed in this fashion.
Consumer demand for safe and wholesome food as well as for acceptable methods by which food products are grown is increasing. The recorded retail prices in this study indicated a large variance for broilers marketed as organic, free-range, and conventional chicken. It appears that the premium prices that consumers are willing to pay for organic and free-range chicken involves more than measurable differences in quantity and quality of meat that were assessed in this study.
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FOOTNOTES |
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Received for publication July 18, 2007. Accepted for publication June 25, 2008.
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