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PROCESSING, PRODUCTS, AND FOOD SAFETY |
* Department of Animal Science, Viale dell’Università, 16, 35020 Legnaro, Padova, Italy; and Veneto Agricoltura, Via S. Gaetano, 74, 36016 Thiene, Vicenza, Italy
1 Corresponding author: chiara.rizzi{at}unipd.it
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONREFERENCES |
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Key Words: organic laying hen • genotype • slaughtering performance • meat quality • sensory evaluation
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONREFERENCES |
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Furthermore, the consumers’ preference for colored-feather and slow-growing meat-type chickens is growing in certain regions of the world. Growing interest regards the appearance (plumage, skin, combs, etc.), meat flavor, and meat texture because these are the main attributes that attract customers to purchase chicken meat (Yang and Jiang, 2005).
There are few indications on the productive performance and quality of the products of local genotypes, and, generally, they refer to chicken (Lewis et al., 1997; Castellini et al., 2002a). Many local breeds are dual-purpose, being able to provide both eggs and meat.
In a previous research study, the productive performance and the quality of eggs of hybrid and Italian-breed laying hens were compared during the first phase of the productive cycle following organic rearing procedures (Rizzi et al., 2002), but no information is currently available on the slaughtering performance, quality, and sensory evaluation of the meat of these genotypes.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONREFERENCES |
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Seventy laying hens belonging to 2 Italian dual-purpose breeds, Ermellinata di Rovigo (ER) and Robusta Maculata (RM), and 2 hybrid strains, Hy-Line White 36 (white eggshell, HLW; Hy-Line Int., Des Moines, IA) and Hy-Line Brown (brown eggshell, HLB), were reared under organic farming production (European Union, 1999).
These local genotypes were created in Veneto, Italy during the 1950s from Sussex and Rhode Island (ER) and Orpington Fulva and White America (RM) purebreds. The color of their eggshell is of brown tonality.
The hens were reared from 24 until 44 wk of age throughout summer and autumn from the months of July to December. The birds were kept under the same prophylaxis procedures, rearing conditions, and feeding treatments from time of hatching until the start of the trial and until the end of the experimental period. Throughout the trial, the photoperiod was 16L:8D, and the environmental temperature (30 to 5° C) and RH (68 to 82%) levels ranged widely from summer to autumn. The birds of each genotype were reared in spaces divided by netting: The outdoor space was 4 m2/bird, and the indoor space was 0.20 m2/bird. Nests (8 birds/nest) and perches (22 cm/bird) were allocated in the indoor space (European Union, 1999). The birds were fed an organic feed ad libitum (Table 1
) having been analyzed for nutrient content (Association of Official Analytical Chemists, 2000).
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At 44 wk of age, 12 birds per genotype were weighed and brought to the slaughterhouse. Feed was withdrawn 12 h before slaughter; the birds, previously weighed were electronically stunned, killed by exsanguination, plucked, and eviscerated (intestines; perivisceral, perineal, and abdominal fat; gall bladder; esophagus; full crop; proventriculus; and spleen). Warm and cold (after 24 h at +4° C) carcass weights were recorded. From the refrigerated carcasses the head, neck, feet, and edible viscera (heart, liver, and gizzard) were removed to obtain the ready-to-cook carcass. Successively, the breast muscles, thighs, drumsticks, and wings were weighed. Finally, the feet, head, and neck were weighed.
pH and Physical Parameters of Breast Meat
On the right breast muscle, superficialis major, at 36 h postmortem, the ultimate pH [by a Delta Ohm HI-8314 pH meter (Delta Ohm, Padova, Italy) and Crison electrode (Crison, Barcelona, Spain)], and color [by a Minolta Chroma Meter CR-300 tristimulus analyzer (Minolta Corp., Ramsey, NJ); CIELAB color space model (Commission International de l’Eclairage, 1976)] were recorded. The CIELAB color space model was chosen to numerically describe the color parameters. Lightness (L*) is the amount of incident light that a surface reflects; – a* values represent green and +a* values represent red color; – b* values represent blue and +b* values represent yellow color.
The skinless breasts were weighed and frozen at – 20° C until cooking. They were removed from the freezer, placed on trays, and thawed in a commercial refrigerator at 3 to 4° C for 24 h. The breast muscles were cooked in water at 70° C for 45 min inside sealed bags. After 15 min of cooling under running water, the fillets were dried.
The shear force was measured by an Instrom equipped with a Warner-Bratzler shear apparatus (Texture Technologies Corp., Scarsdale, NY) on cores with cross-sectional areas of 1.25 cm2 obtained from the breast. The samples were cut perpendicular to the fiber direction.
The breasts were weighed before and after thawing and cooking to evaluate thawing and cooking loss.
Sensory Evaluation of Meat
Left skinless breast and thighs were analyzed following the sensory profile procedure (International Standards Organization, 2003).
Breasts and thighs were cooked in a prewarmed 200° C oven to a final temperature of 75° C. Internal temperatures were monitored with a handheld thermometer. Thigh cooking required 20 min more than the breast. Samples were removed from the oven and tempered 15 min in the pan before preparation for the sensory analysis.
Samples were prepared by cutting a 2-cm-wide strip parallel to the fibers. This strip was then cut into 2 or 3 cubes of 2 cm. Samples were placed in prewarmed glass custard dishes that were nested in coded Styrofoam cups to maintain the serving temperature (50° C). Sample containers were coded with 3-digit numbers and presented to panelists in individual sensory workstations equipped with computers for data collection using FIZZ Network software (FIZZ version 2.10, Biosystems, Couternon, France). Panelists used 1 cube for odor and flavor and 1 cube for texture to evaluate the intensity of the sample attributes and mark the responses on 10-point scales (Table 2).
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The sensory attributes and definitions used by the descriptive panel to evaluate cooked breast and thigh meat are detailed in Table 2
. Odor, flavor, and texture terms represented different phases of evaluation. The lexicon of odor, aroma, and texture terms was developed previously by the trained descriptive sensory panel.
The sample cooking and presentation to panelists followed a monadic sequence at 20-min intervals to allow for fatigue recovery between samples. Sensory evaluations were replicated 4 times. Sample order presentations to panelists were randomized across sessions.
Statistical Analysis
All data on slaughtering performance and chemical and physical properties of meat were subjected to 1-way ANOVA as a completely randomized design, with genotype as main effect, using the GLM procedure of SAS (SAS Institute, 2000).
Significant differences among the means were determined using Duncan’s multiple range test (SAS Institute, 2000).
Data on sensory evaluation were analyzed using the FIZZ Statistical Calculation and SYSTAT 10 (Biosystems) for sensory data. This multivariate analysis procedure is used in sensory profiling to analyze genotype effect, panelist effect, and attribute performance. Genotype means are subsequently plotted in a 2-dimensional space to visualize their relationships according to a reduced set of factors derived from the attributes.
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RESULTS AND DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONREFERENCES |
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Slaughtering Performance
In Table 3, the live BW and slaughtering performance of the hens are reported.
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Dressing percentage was higher in the local breeds (P < 0.01) than in the hybrids, as their carcass conformation and body dimensions recall those of genotypes with characteristics for meat production. Within the hybrid and local groups, the RM and HLB values were significantly (P < 0.05) higher than ER and HLW, respectively.
The breast weight significantly (P < 0.01) differed among the 4 genotypes as well as the thighs, drumsticks, and wings: The RM hens showed the highest values, followed by the ER (P < 0.01) and HLB (P < 0.01), whereas the HLW showed the lowest weight (P < 0.01).
The breast percentage was higher (P < 0.01) in RM than in HLB, HLW, and ER carcasses. The thigh and drumstick incidence was higher (P < 0.01) in purebred carcasses than in the hybrids and, within local genotypes, in the ER hens rather than (P < 0.05) in the RM. The wing percentage was higher (P < 0.01) in the HLB carcasses compared with the other groups.
The muscle-bone ratio of the thigh did not differ among the groups, whereas in the drumstick, it was higher (P < 0.05) in the RM group and lower (P < 0.05) in the HLW hens. The ER and HLB samples were intermediate.
As far as the slaughtering wastes are concerned, the incidence of the head and neck was lower (P < 0.01) in the purebreds than in the hybrids. Furthermore, HLB (P < 0.05) and RM (P < 0.01) hens presented lower values than HLW and ER, respectively.
The feet incidence was higher (P < 0.01) in the ER carcasses and lower (P < 0.01) in the RM; the hybrids were intermediate.
The different response in terms of live BW and slaughtering performance observed among the 4 genotypes is related to their genetic assessment.
All of the birds exhibited poor weight gains (Rizzi et al., 2002) throughout the trial, having reached sexual maturity and on laying activity. However, the Italian breeds showed higher body increments and lower laying activity (Rizzi et al., 2002) compared with the hybrids, because they are dual-purpose genotypes simultaneously exhibiting a discrete egg production and meat growth.
Genetic improvements carried out during these years on the hybrid strains of hens have focused on egg production and, therefore, although this has allowed the obtaining of higher egg yields, muscle growth is limited. The impossibility of concurrently improving these 2 characters due to the negative correlations between them is well established (Bell, 2002).
Although the egg yield was substantially similar between hybrids (85%, Rizzi et al., 2002), some differences in slaughtering performance were observed. These differences are the expression of a different genetic assessment given that the genetic origin of these 2 strains is different. The white eggshell strain originates from White Leghorn and presents high egg-laying capability and low body mass and feed consumption.
Otherwise, the meat of spent hens met a part of the entire poultry meat production, and the carcass should present a satisfactory level of meatiness. Therefore, in the brown eggshell hybrid strains, geneticists also utilize lines or breeds with carcass characteristics useful for meat production, such as the dual-purpose breeds Barred Ply-mouth Rock, Rhode Island Red, Rhode Island White, Australorp, New Hampshire, and others (Scott and Silversides, 2000).
In addition, the 2 Italian breeds, with different genetic origins from European, American, or both purebreds, presented differences on some productive (Rizzi et al., 2002) and carcass characteristics.
pH and Physical Characteristics of Breast Meat
In Table 4, the breast pH and some physical parameters are reported.
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The meat color could be affected by the movement of the birds and thus by a more or less intense muscular activity. In these experimental conditions, the hens were allowed to move outdoors and indoors over the 24 h, and they showed similar motorial activity. Therefore, it is not possible to attribute the differences found among the genotypes to exercise.
Genotype could modify muscle color, as observed by Le Bihan-Duval et al. (1999) in breast muscles of broilers of different genetic lines. Color differences may also be due to myoglobine content in the muscle and to the final pH (Berri et al., 2001).
Our results agree with those of other authors (Le Bihan-Duval et al., 1999), who found a negative correlation between the final pH of the muscle and the L value.
Higher (P < 0.01) thawing losses were observed in local and HLW genotypes. The HLW breast presented higher (P < 0.01) cooking losses when compared with the other groups. Within the local breeds, the RM samples exhibited lower (P < 0.01) losses than the ER breasts. Higher total weight losses were observed in ER and HLW breasts, indicating that final pH and other factors such as breast muscle growth characteristics may influence them. Our results agree with those of Kok et al. (2005), who found a significant relationship between the weight of the fillets and the cooking loss, which is higher in smaller fillets.
The shear force (Table 4) was similar in the 4 groups. The absence of significant differences among the genotypes could be due to the type of sample used. In fact, in our trial the shear force was tested on cooked breast meat after thawing. In organic farming production, it might be necessary to slaughter the birds only during certain periods of the year and not in cold seasons (to avoid extreme environmental cold temperature and an excessive increase of feed consumption), and, therefore, the meat has to be frozen. However, in the intensive production system, which is carried out only indoors, the production is extended throughout the year.
Freezing and thawing procedures could have altered some physical properties of the meat, and in these conditions, small variations of meat tenderness of genotypes could not be perceived by instruments.
Sensory Profile of Breast and Thigh Meat
The meat odor and flavor properties and texture characteristics are presented in Table 5.
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) instead of grass, which grew very little during the hot summer and grew in very limited areas during the autumn. The odor intensity did not differ among the genotypes for either the breast or thigh. The values for the thigh are higher than those of the breast; such differences could be due to muscle composition, because the thigh had a higher lipid content than the breast, in addition to being chemically different (C. Rizzi, unpublished data). In fact, the lipid content of the meat and its chemical composition may imply relevant differences in the scores between breast and thigh meat; flavor was higher in the thighs than in the breasts, particularly when fish oil was added to the diet instead of vegetable oil (Lopez-Ferrer et al., 1999).
Aroma intensity was similar among the groups in the breast but not in the thigh, which presented higher values (P < 0.05) in the hybrids. The variability of this parameter between breast and thigh meat seems to be related to the genotype. Chemical reactions during cooking release many substances, such as volatile compounds, that give aroma and flavor to the meat (Aliani and Farmer, 2005).
It is worth noting that these attributes may be particularly affected by the concentrations of lipids and other compounds of raw meat, such as reduced and phosphorylated sugars, amino acids, and thiamine (Aliani and Farmer, 2005). The natural components have little aroma until they interact during cooking; the reactions include lipid oxidation, the thermal degradation of thiamine, and the Maillard reaction between an amino compound (amine, amino acid, peptide, or protein) and a carbonyl compound (Aliani and Farmer, 2005).
Table 5 presents the shear resistance of the breast meat; it was higher (P < 0.01) in the ER and HLW samples compared with the HLB and RM as well as in the thigh (P < 0.01).
Table 6 summarizes some texture attributes of the breast and thigh.
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The opposite was observed in the thigh; the RM samples showed significantly (P < 0.05) lower adhesivity than ER. More relevant differences were observed between the muscles of ER and RM hens compared with the hybrids.
Breast fibrousness was significantly higher (P < 0.05) in RM and ER samples compared with HLB (P < 0.05). Thigh meat presented higher (P < 0.05) values in ER and HLW when compared with RM; HLB was intermediate. Thigh meat presented higher fibrousness than breast meat, probably due to higher muscular activity, as previously stated by Castellini et al. (2002b).
Chewiness was lower (P < 0.01) in HLW compared with RM breast; the other genotypes were intermediate. No differences were observed in thigh meat.
Breast solubility was higher (P < 0.01) in HLB compared with the other groups. Thigh solubility was higher (P < 0.05) in RM than in both ER and HLW. Generally, these 2 last parameters presented lower values in thigh muscles than in breast muscles.
The same trend of breast solubility was observed in breast juiciness, with higher values (P < 0.01) in the HLB hens. The thigh juiciness was similar among the groups. In the present trial, the notable differences in juiciness were observed between hybrids only in the breast, but not in the thigh. Different scores were given by panelists to the thighs and breasts; the score difference was minimal only for HLB.
These results could indicate the positive effects of the genetic improvement carried out in recent years on the brown eggshell genotypes to obtain carcass meat with acceptable quality; higher juiciness in HLB is partly attributable to the higher fat content (Lawrie, 1991) of muscles (C. Rizzi, unpublished data).
Furthermore, in our trial, the juiciness reflects the trend of water loss data, according to Kok et al. (2005), as meat with higher scores presented the lowest total losses (thawing and cooking).
Different (P < 0.01) breast tenderness was observed among the 4 groups: HLW presented the lowest (P < 0.01) tenderness, followed by ER (P < 0.01) and RM (P < 0.01), whereas the HLB showed the highest (P < 0.01). In the thighs, significantly higher (P < 0.01) values were found in hybrid samples respect to local genotypes. Local breeds presented similar tenderness both for breast and thigh, whereas the hybrids showed similar values only in the thigh.
Variations of meat texture, particularly juiciness and hardness, could be related to the structure and to the acidic composition of the lipid fraction of the muscles, and many factors are able to influence them (Farmer et al., 1997; Castellini et al., 2002b; Lyon et al., 2004).
Recently, Jahan et al. (2005) pointed out that the primary difference among chicken breasts from differing production regimens (organic, free-range, corn-fed, and conventional) was mainly by appearance and texture, and less by aroma and flavor.
The effect of age on meat tenderness caused by the changing of muscle structure, in particular by increasing collagen content, is well established (Touraille et al., 1991; Castellini et al., 2002b). The increasing of the saturated fraction, with a consequent increase of melting point, or the increasing of protein content could result in drier and firmer meat (Du and Ahn, 2002).
In the present trial, differences in breast tenderness could be due to protein and lipid content, because breasts with higher lipid and lower protein content (C. Rizzi, unpublished data) showed higher tenderness. The saturated fatty acid content of the thighs, which tended to be higher in the local breeds, may be one of the factors that influenced meat tenderness.
In any case, it is worth noting that for breast samples only 1 muscle and i.m. lipids were considered, whereas for thigh samples more than 1 muscle and both i.m. and intermuscular fats were included.
Furthermore, according to Girolami et al. (2003), the differences in meat tenderness were detected by the sensory panel, whereas instrumental measures were not able to detect any difference. It is worth stating that the Warner-Bratzler method gives the maximum force needed to shear a core of meat, whereas information on perception of meat tenderness may be detected during biting and chewing. Similar responses were observed between shear resistance to the knife and the tenderness data for the breast, but not the thigh, probably because thigh samples were comprehensive of more muscles and were thus less homogeneous with respect to the breast.
The results give some indications on meat production of the 4 studied genotypes of laying hens reared under organic conditions in the first phase of the productive cycle. The local breeds demonstrated good capability in terms of meat production performance, presenting carcasses with heavier commercial cuts and higher fleshiness.
The panel test results point out that none of the genotypes presented a global sensorial profile better than another. The major effect of genotype involved the texture parameters rather than those concerning odor and flavor characteristics. The RM and HLB hens presented breast muscles with more tenderness and juiciness. Generally, the sensorial results observed on the breast do not agree with those of the thigh.
Further research is needed to determine meat yields and meat quality of hens of these genotypes reared under environmental and dietary conditions different from those studied in this trial and in a different phase of the laying cycle.
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ACKNOWLEDGMENTS |
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Received for publication March 23, 2006. Accepted for publication August 4, 2006.
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