Influence of Genotype on Meat Quality in Laying Hens after the Egg Production Season

Abstract

The aim of this study was to compare the quality characteristics of the meat of two genotypes (Lohmann Brown and Lohmann White) of laying hens after the laying period. Studies were conducted on pectoral and leg muscles from 26 females, 13 of each genotype. Breast and leg muscles were evaluated in terms of their basic chemical composition, acidity (pH₂₄), color attributes (L*, a*, b*), electrical conductivity (EC₂₄) and macro- (K, P, Na, Mg, Ca) and microelements (Fe, Zn, Cu, Mn, Cr). Analysis of the texture of the pectoral muscle major and rheological properties (sum of viscosity modules and sum of elasticity modules) was also performed. Breast and leg meat were also subjected to sensory evaluation. The genotype of the birds significantly affected the percentage of intramuscular fat in the pectoral muscle and the percentage of protein, fat and water in the leg muscle. When analyzing pectoral and leg muscles for color attributes, we found no significant (p > 0.05) differences between genotypes. Differences were shown, however, between genotypes in EC₂₄ and phosphorus content in leg muscle. Breast muscles differed significantly (p < 0.05) in iron and zinc content. Sensory analysis revealed significant differences between genotypes in leg muscle tenderness and juiciness, and breast muscle juiciness and aroma desirability. When analyzing the breast muscle in terms of texture, we did not observe any significant differences, nor did we find any differences in the assessment of rheological properties. Not depending on genotype, however, we noted significant differences between protein, fat, water and collagen content, sodium, magnesium, calcium, iron, zinc, copper, manganese, chromium, acidity, color parameters (L*, a*, b*), EC₂₄ and tastiness desirability between breast meat and leg meat. The results of this study showed that meat from old hens obtained after the laying period is a good material for further technological processing, due to its favorable basic chemical composition and high nutritional value expressed in the content of macro- and microelements, and is also characterized by relatively good sensory characteristics, which can be improved by marinating or adding enzymatic preparations during its processing.

1. Introduction

Global production of table eggs in 2021 reached 86.3 million tonnes [1]. China is the largest producer of table eggs, supplying about 35% of world production [1]. The European Union is only in fourth place, with a share of 6% of world production. The leaders in 2022 were France and Germany; Poland ranked sixth, and its share of the production of table eggs in the EU amounted to 8% [2]. In Poland in 2020, more than 10 billion table eggs were produced [3]. The main commercial hybrids of laying hens kept in Poland are Rosa, Hy-line, Bovans, Lohmann, Messa, and Isa Brown [4]. For more than 50 years, Lohmann Selected Leghorn and Lohmann Brown have been among the world’s leading commercial laying hybrids [5]. Lohmann Brown is the result of a cross between Rhode Island and White Rock, which begin egg production at about 19 weeks of age. The laying period lasts continuously up to about 72 weeks, during which one Lohmann Brown laying hen lays about 315 brown-shelled eggs, while a Lohmann White lays 321 white-shelled eggs. The body weight at the end of the laying period ranges from 1.90 to 2.10 kg for Lohmann Brown and from 1.72 to 18.7 kg for Lohmann White [6]. After the production period, the laying hens are replaced and the old hens are sent to the slaughterhouse [7].

Poultry meat is one of the most popular meats in the world, with consumption of 132.4 million tonnes in 2021 [8]. The demand for poultry meat is constantly growing and exceeds production capacity, so one of the solutions to the increased consumer demand may be to use post-production laying hens for the processing industry [9]. It is estimated that around 7% of the world’s poultry production consists of laying hens and post-laying parent flocks [10].

Meat that comes from laying hens after the production period is not readily consumed due to poor organoleptic and sensory properties, while there are countries where old chickens are a delicacy and traditional dishes are prepared from them, e.g., Thailand’s tom yum soup or broths with a strong aroma in Africa [10,11]. Choe and Kim [12], on the other hand, have shown that meat from old chickens is characterized by high levels of myofibrillar protein and omega-3 fatty acids. Nevertheless, due to a lack of consumer interest, the prices of carcasses and meat of old laying hens on the market are low [9,12,13]. Therefore, meat from laying hens or breeding flocks after the production period is mainly used for the production of canned food as well as for the production of pet food [10].

Among the factors that determine the nutritional value and suitability for processing, we can identify the age of the bird, the housing system used and the nutrition provided to the birds; genetic and environmental conditions also play a very important role [14]. According to Bhaskar Reddy et al. [15], the most important factors that affect the quality of poultry meat include pH, thermal leakage, water retention capacity, muscularity, fiber diameter, myoglobin content, collagen and protein extract content, chemical composition and sensory characteristics.

The fact that a large number of birds are slaughtered every year and then used in some parts of the world for animal feed production led us to carry out a comparative analysis of two genotypes of laying hens after the production period. Lohmann Brown and Lohmann White were analyzed after the laying period (83 weeks) in terms of basic chemical composition, physicochemical properties (pH and color), content of selected minerals and sensory properties of pectoral and leg muscles. An analysis of the cardboard features of the pectoral muscle major was also carried out. These analyses determined the nutritional value, technological suitability and culinary suitability of meat from laying hens after the production period.

2. Materials and Methods

2.1. Experiment Animals

The study was carried out on 26 carcasses of Lohmann Brown (LB, n = 13) and Lohmann White (LW, n = 13) laying hens after laying at 83 weeks of age. We received information regarding the genotype and age of the hens, the housing system and environmental and nutritional conditions from the contracting department of the poultry slaughterhouse. Layers during the egg production period were kept in cages in the same poultry house, without windows and access to runways on a commercial farm. During egg production, birds were fed a complete diet containing 16.5% CP, 11.6 MJ ME, 0.34% Met, 0.81% Lys, 3.5% Ca, 0.61% P and 0.15% Na intended for laying hens. The temperature in the chicken coop was 20 °C and the relative humidity ranged from 65 to 75%. After the laying period, the birds were transported to a commercial slaughterhouse where they were slaughtered.

2.2. Carcass Analysis

After slaughter, the eviscerated carcasses with necks were transported in a refrigerated truck at a temperature of 4 °C degrees for 1 h to the University, where they were refrigerated at 2 °C (Hendi, Robakowo, Poland) for 18 h. After cooling, the carcasses were dissected using the simplified method described by Ziołecki and Doruchowski [16]. The carcasses were dissected into the following cuts: wings with skin, neck without skin, leg muscle, breast muscle, abdominal fat, skin with subcutaneous fat, and remainder of the carcass. Analyses were performed on isolated pectoral and leg muscles.

2.3. Physicochemical Analysis

Acidity (pH₂₄) and EC₂₄ of the pectoralis major and leg muscles were measured 24 h after slaughter. The pH₂₄ was measured using a pH-Star CPU pH-meter equipped with a glass electrode in a steel knife (Elmetron, Zabrze, Poland). The measurement was made with an accuracy of 0.01. The electrical conductivity was performed using the LF-Star CPU (Ingenieurbüro R. Matthäus, Nobitz, Germany) with an accuracy of 0.1 mS/cm. The measurement analysis was performed by placing the conductometer electrode at an angle of 90 °C along the muscle fibers. Next, the color analysis of pectoralis and thigh muscles was performed using the MINOLTA CR 400 colorimeter (Konica Minolta Poland, Chiyoda, Japan). Muscles were evaluated in terms of color L* (lightness), a* (redness) and b* (yellowness). The pH₂₄ measurement was repeated 3 times for each sample.

To determine the basic chemical composition of the meat, 90 g of breast meat and 90 g of leg meat from each carcass were used; then, the samples taken were minced. An electric meat grinder (Zelmer, Rzeszow, Poland), which was equipped with a 2 mm diameter mesh, was used for grinding. FoodScan (FoodScan, Hillerød, Denmark) was used to determine the water, collagen, protein and fat content, and near-infrared transmission spectroscopy (NIT) was applied.

Dissolution of muscle samples was carried out using a high-pressure microwave digester (Speedwave Xpert, Berghof, Eningen, Germany). Approximately 0.500 ± 0.001 g of muscle dry weight each was digested in 6.0 mL of a mixture of concentrated acids, HNO3 and HClO4 (ultra pure, Merck, Darmstadt, Germany; acid ratio 5:1). After digestion, the samples were diluted with Milli-Q (18.2 MΩ) water to 25 mL. The elements in the diluted muscle samples were then determined. Minerals were determined using a Hitachi ZA3000 atomic absorption spectrophotometer (Hitachi High-Technologies Corporation, Tokyo, Japan). Macroelements (Ca, K, Mg, Na) were determined using the flame atomic absorption technique (FAAS) in an air–acetylene flame. Microelements (Cr, Cu, Fe, Mn, Zn) were determined by the graphite furnace atomic absorption technique (GFAAS). Phosphorus was determined by the colorimetric method using ammonium molybdate and ascorbic acid as a reducing agent. Absorbance was measured using a Hitachi U-2900 UV-VIS spectrophotometer (Hitachi High-Technologies Corporation, Tokyo, Japan). Calibration curves were performed using certified standard solutions (1000 mg/L) from Scharlau (Barcelona, Spain) for Ca, Fe, K, Mg and Na and from Merck (Germany) for Cu, Cr, Mn, P and Zn. The accuracy of the analytical method was tested using Dogfish Liver NCR-DOLT-5 reference material (National Research Council Canada). Elemental recoveries were 93% (for Cr), 98% (for Zn), 99% (for Mg), 101% (for Cu), 103% (for Fe, Mn), 104% (for Ca), 106% (for K), 107% (for P) and 114% (for Na).

2.4. Sensory Evaluation

The sensory properties of the pectoral muscles and legs were assessed. A 0.6% brine solution was prepared in which the meat samples were boiled. Then, six trained judges determined the tenderness, juiciness, intensity and desirability of the tastiness and aroma. The 5-point scale described by Baryłko-Piekielna and Matuszewska [17] was used for the assessment. The score ranged from 5 (highest) to 1 (lowest).

2.5. Meat Texture

The pectoralis major muscle was used to analyze texture and rheological properties. The precooked samples were heated to 70.2 °C and then cooled to 12 °C. Texture (hardness, springiness, cohesiveness, chewiness, gumminess and WB shear force) was assessed according to texture profile analysis (TPA) procedures and Warner–Bratzler (WB) protowheels. Analysis of the measurements was performed using a Stable Micro Systems TA.XT Plus apparatus (Stable Micro Systems, Godalming, UK). In the TPA test, a 0.62 cm diameter plunger was inserted into the specimen twice, parallel to the direction of the muscle fibers, to a depth of 80% (16 mm) of its height. A 50 N load cell was used, and the speed of the crossbar was set at 50 mm/min. The hardness, cohesiveness, springiness, chewiness and gumminess of the meat were calculated from the strange-deformation curve obtained by the TPA test. Hardness was calculated as the maximum height of the first peak, cohesiveness as the ratio of the area of the second peak to the area of the first peak, springiness as the width of the base of the rising portion of the second peak, gumminess as the product of hardness and cohesiveness, and chewiness as the product of hardness, cohesiveness and springiness [18].

The rheological properties were evaluated with Intron 1140 (Intron, Boston, MA, USA), applying the relaxation test, during which a stylus with 0.96 cm diameter was inserted 2 mm into the sample (deformation of 10%), registering strain changes for 90 s. Modules of springiness and viscosity were calculated with the Generalized Maxwell model comprising a Hooke body connected in parallel with two Maxwell bodies [19]. The equation in this model is as follows:

$$\delta =\epsilon \cdot \left[E_0+E_1\cdot \exp \left(\frac{-E_1\cdot t}{{\mu }_1}\right)+E_2\cdot \exp \left(\frac{-E_2\cdot t}{{\mu }_2}\right)\right]$$

where δ—is the tension (kPa), ε—is the deformation, E₀—is the modulus of elasticity of Hooke’s body (kPa), E₁, E₂—are the moduli of elasticity of Hooke’s body 1 and 2, respectively (kPa), µ₁, µ₂ are the moduli of viscosity of Maxwell’s body 1 and 2, respectively (kPa × s), and t—is the time.

In order to better interpret the results for each test, the sum of the moduli of elasticity (E₀ + E₁ + E₂) and the sum of viscosity moduli (µ₁ + µ₂) were calculated for each sample.

2.6. Statistical Analysis

The results obtained in this experiment were subjected to analysis of variance. Using the Statistica 13.3 PL computer program, the arithmetic mean and standard deviation, as well as the standard error of the mean (SEM), were calculated for each assessed trait (total for two genotypes). The significance of differences (p < 0.05) between genotypes and between breast meat and leg meat characteristics (without taking into account genotype) was verified using Tukey’s post hoc test.

3. Results

3.1. Physicochemical Properties

Comparing two genotypes of laying hens in terms of pH₂₄ of breast and leg muscles, we found no significant differences (

Table 1. Selected physicochemical traits of meat of laying hens at 83 weeks.

Item		Lohmann Brown	Lohmann White	SEM	p Value
					Genotype	Muscle
Acidity—pH24	PM	5.99 ± 0.2	6.03 ± 0.1 y	0.1	0.643	0.001
	LM	6.13 ± 0.1	6.20 ± 0.2	0.1	0.168
Conductivity—EC24 (mS/cm)	PM	11.8 ± 1.0	11.3 ± 1.0 y	0.2	0.261	<0.001
	LM	10.8 a ± 0.8	9.7 b ± 1.6	0.2	0.032
Lightness—L*	PM	45.2 ± 2.5	45.0 ± 2.6 y	0.5	0.877	0.018
	LM	42.4 ± 4.1	43.6 ± 3.0	0.7	0.381
Redness—a*	PM	3.9 ± 1.5	4.6 ± 1.9 y	0.3	0.324	<0.001
	LM	11.8 ± 3.3	9.8 ± 4.6	0.9	0.204
Yellowness—b*	PM	3.4 ± 1.7	3.7 ± 1.5 y	0.3	0.660	0.009
	LM	5.6 ± 3.3	4.5 ± 4.6	0.5	0.244

Note: Values are expressed as means ± standard deviation, n = 13/genotype, PM—pectoral muscle, LM—leg muscle. ^a,b p < 0.05—means with different superscripts are statistically different between genotypes. ^y p < 0.05—statistically significant differences between pectoral muscle and leg muscle regardless of genotype.

), but there were significant (p < 0.05) differences between the acidity of breast and leg muscles regardless of genotype (average breast—6.02 versus leg—6.17). Analyzing pectoral muscles for EC₂₄, we found no significant effect of genotype on the studied trait, while genotype significantly affected the analyzed trait of leg muscles. Lohmann White (LW) leg muscles had a lower EC₂₄ compared to Lohmann Brown (LB) leg muscles.

We also showed significant differences between pectoral and leg muscles independent of genotype in terms of EC₂₄; pectoral muscles (EC₂₄—11.6) had a significantly higher EC₂₄ compared to leg muscles (EC₂₄—10.3) as evidenced by p < 0.001. We did not show a significant effect of genotype on pectoral and leg muscles in terms of meat color L* (lightness), a* (redness) and b* (yellowness). In contrast, we showed significant differences between breast and leg muscles in terms of color (L*, a*, b*) independent of genotype. Leg muscles were characterized by significantly higher color saturation a* and b* and lower lightness (L*) compared to pectoral muscles as evidenced by p-values from <0.001 to 0.018.

3.2. Chemical Composition

The basic chemical composition of pectoral and leg muscles is shown in

Table 2. The basic chemical composition of meat of laying hens at 83 weeks.

Item		Lohmann Brown	Lohmann White	SEM	p Value
					Genotype	Muscle
Protein, %	PM	25.2 ± 0.4	25.1 ± 0.3 y	0.1	0.410	<0.001
	LM	19.6 a ± 0.3	19.0 b ± 0.8	0.1	0.049
Intramuscular fat, %	PM	0.9 a ± 0.1	0.8 b ± 0.1 y	0.1	0.005	<0.001
	LM	8.6 b ± 1.4	9.9 a ± 1.3	0.3	0.028
Water, %	PM	72.1 ± 0.3	71.9 ± 0.3 y	0.1	0.097	<0.001
	LM	68.7 a ± 1.2	67.5 b ± 1.3	0.3	0.020
Collagen, %	PM	1.5 ± 0.2	1.4 ± 0.1 y	0.1	0.190	<0.001
	LM	2.0 ± 0.2	2.0 ± 0.2	0.1	0.394

Note: Values are expressed as means ± standard deviation, n = 13/genotype, PM—pectoral muscle, LM—leg muscle. ^a,b p < 0.05—means with different superscripts are statistically different between genotypes. ^y p < 0.05—statistically significant differences between pectoral muscle and leg muscle regardless of genotype.

. We demonstrated a significant (p < 0.05) effect of genotype on the percentage of intramuscular fat in pectoral muscle as evidenced by p = 0.005. LB pectoral muscles had a 0.1% higher level of intramuscular fat compared to LW pectoral muscles. In the other pectoral muscle traits analyzed, genotype had no effect. In contrast, genotype had a significant effect on the percentage of water, protein and intramuscular fat in leg muscle. LB leg muscles were characterized by higher water and protein content and lower intramuscular fat content compared to LW leg muscles. Not dependent on genotype, we also observed significant differences in analyzed traits between pectoral and leg muscles. Thoracic muscles were characterized (p < 0.05) by higher percentages of protein and water, and lower intramuscular fat and collagen compared to leg muscles.

In

Table 3. Content of selected macro- and micronutrients in meat of laying hens at 83 weeks.

Item		Lohmann Brown	Lohmann White	SEM	p Value
					Genotype	Muscle
Macroelements (mg/100 g of meat)
K—potasium	PM	288.4 ± 29.3	276.3 ± 13.5	4.5	0.309	0.434
	LM	287.1 ± 28.1	295.1 ± 47.1	7.4	0.685
P—phosphorus	PM	250.0 ± 14.9	238.6 ± 12.1	3.6	0.112	0.302
	LM	257.5 a ± 27.4	213.4 b ± 11.9	7.6	0.001
Na—sodium	PM	54.2 ± 6.8	54.8 ± 7.6 y	1.8	0.876	<0.001
	LM	81.3 ± 12.2	80.1 ± 11.4	2.2	0.830
Mg—magnesium	PM	26.8 ± 1.7	26.9 ± 1.1 y	0.4	0.828	<0.001
	LM	23.7 ± 2.1	23.3 ± 2.5	0.6	0.735
Ca—calcium	PM	3.5 ± 1.0	3.3 ± 0.3 y	0.2	0.446	<0.001
	LM	5.0 ± 1.5	4.9 ± 0.7	0.3	0.823
Microelements (mg/100 g of meat)
Fe—iron	PM	0.428 b ± 0.09	0.532 a ± 0.13 y	0.1	0.049	<0.001
	LM	1.248 ± 0.30	1.370 ± 0.18	0.1	0.346
Zn—zinc	PM	0.230 b ± 0.03	0.388 a ± 0.18 y	0.1	0.035	<0.001
	LM	1.541 ± 0.33	1.775 ± 0.33	0.1	0.181
Cu—copper	PM	0.032 ± 0.01	0.033 ± 0.01 y	0.1	0.757	<0.001
	LM	0.071 ± 0.01	0.073 ± 0.01	0.1	0.753
Mn—manganese	PM	0.010 ± 0.01	0.009 ± 0.01 y	0.1	0.262	<0.001
	LM	0.019 ± 0.01	0.022 ± 0.01	0.1	0.274
Cr—chrome	PM	0.002 ± 0.01	0.002 ± 0.01	0.1	0.990	0.033
	LM	0.002 ± 0.01	0.003 ± 0.01	0.1	0.114

Note: Values are expressed as means ± standard deviation, n = 13/genotype, PM—pectoral muscle, LM—leg muscle. ^a,b p < 0.05—means with different superscripts are statistically different between genotypes. ^y p < 0.05—statistically significant differences between pectoral muscle and leg muscle regardless of genotype.

, we present the content of selected macro- and micronutrients in pectoral and leg muscle. We show a significant (p < 0.05) effect of genotype on the contents of iron (Fe) and zinc (Zn) in pectoral muscle and phosphorus (P) in leg muscle. LB pectoral muscles had lower Fe and Zn contents compared to LW pectoral muscles, while LB leg muscles had higher P levels compared to LW leg muscles. The other determined mineral contents in breast meat, which were potassium (K), phosphorus (P), copper (Cu), manganese (Mn), chromium (Cr), magnesium (Mg), sodium (Na) and calcium (Ca), and for leg muscles were potassium (K), copper (Cu), manganese (Mn), chromium (Cr), magnesium (Mg), sodium (Na), calcium (Ca), iron (Fe) and zinc (Zn), were not affected by genotype. Independent of genotype, we showed significant differences between pectoral muscle and leg muscle in macronutrient content for Na, Mg and Ca and the microelements Mn, Cu, Zn and Fe. Significantly (p < 0.05) higher values of Na, Ca, Fe, Zn, Cu and Mn were characterized by leg muscles compared to pectoral muscles, while Mg content was significantly higher in pectoral muscle than in leg muscle as evidenced by the p-value < 0.001.

3.3. Sensory Evaluation

Analyzing the pectoral and leg muscles in terms of sensory evaluation (

Table 4. Selected sensory traits of meat of laying hens at 83 weeks.

Item		Lohmann Brown	Lohmann White	SEM	p-Value
					Genotype	Muscle
Tenderness, pts.	PM	2.9 ± 0.2	2.8 ± 0.2	0.1	0.671	0.065
	LM	3.2 a ± 0.3	2.9 b ± 0.4	0.1	0.018
Juiciness, pts.	PM	3.1 a ± 0.2	2.8 b ± 0.2	0.1	0.006	0.124
	LM	3.3 a ± 0.3	2.9 b ± 0.3	0.1	0.011
Aroma intensity, pts.	PM	3.7 ± 0.3	3.8 ± 0.3 y	0.1	0.568	<0.001
	LM	3.3 ± 0.4	3.3 ± 0.2	0.1	0.905
Aroma desirability, pts.	PM	3.0 b ± 0.2	3.2 a ± 0.2	0.1	0.018	0.199
	LM	3.1 ± 0.4	3.2 ± 0.4	0.1	0.591
Tastiness intensity, pts.	PM	3.2 ± 0.3	3.1 ± 0.3	0.1	0.639	0.944
	LM	3.2 ± 0.4	3.1 ± 0.2	0.1	0.479
Tastiness desirability, pts.	PM	2.8 ± 0.2	2.8 ± 0.2 y	0.1	0.701	<0.001
	LM	3.2 ± 0.2	3.1 ± 0.3	0.1	0.678

Note: Values are expressed as means ± standard deviation, n = 13/genotype, PM—pectoral muscle, LM—leg muscle. ^a,b p < 0.05—means with different superscripts are statistically different between genotypes. ^y p < 0.05—statistically significant differences between pectoral muscle and leg muscle regardless of genotype.

), we showed a significant effect of genotype on the traits analyzed. LB pectoral muscles were characterized by higher juiciness and worse aroma desirability compared to LW pectoral muscles. In contrast, LB leg muscles were characterized by significantly (p < 0.05) higher tenderness and juiciness compared to LW leg muscles. Significant differences were also found between pectoral and leg muscles not depending on genotype in the evaluation of flavor intensity and tastiness desirability. Breast muscles were characterized by higher aroma intensity, while leg muscles were characterized by more desirability.

3.4. Meat Texture

Analyzing the texture of the pectoralis major muscle and rheological properties (sum of viscosity moduli, sum of elasticity moduli), we did not note a significant (p < 0.05) effect of genotype on the studied traits (

Table 5. Some textural and rheological traits of pectoralis major muscle of laying hens at 83 weeks.

Item	Lohmann Brown	Lohmann White	SEM	p-Value
WB shear force (N)	70.0 ± 16.2	71.4 ± 16.8	3.2	0.831
Hardness (N)	32.9 ± 5.4	35.4 ± 5.9	1.1	0.277
Cohesiveness	0.4 ± 0.1	0.4 ± 0.1	0.1	0.211
Springiness (cm)	1.5 ± 0.1	1.4± 0.1	0.1	0.602
Chewiness (N × cm)	18.6 ± 4.5	20.9 ± 5.1	0.9	0.229
Gumminess (N)	12.8 ± 2.9	14.4 ± 3.7	0.7	0.236
Sum of elastic moduli (kPa)	375.4 ± 63.3	351.7 ± 52.1	963.0	0.308
Sum of viscous moduli (kPa × s)	17,795 ± 5439	15,906 ± 4329	11.4	0.308

Note: Values are expressed as means ± standard deviation, n = 13/genotype. No statistically significant differences were found.

). Nevertheless, the LB pectoralis muscle was characterized by better parameters expressed in WB shear force and hardness, with less gumminess and better chewiness characteristics compared to the LW pectoralis muscle. Also, the obtained results for the rheological properties were higher in LB hens than LW.

4. Discussion

Poultry meat is a very important part of the human diet because it has high dietary and nutritional qualities, and yet it is relatively inexpensive compared to pork or beef. It is also an excellent source of protein, vitamins, unsaturated fatty acids and macro- and microelements [20]. One of the main factors that influence the purchase of poultry meat is its color. A large proportion of consumers, more than 74%, are guided by its appearance when choosing meat [21]. Meat color and fattiness, which from the consumer’s point of view determine demand, are influenced by factors such as age, sex, genotype, nutrition and housing system [11,21]. In our study, the genotype of the birds did not significantly affect the color of the pectoral and leg muscles. The Lohmann Brown (LB) and Lohmann White (LW) breast muscles evaluated in our study were characterized by lower L*, a* and b* color saturation than the breast muscles of Hi -Line Brown laying hens at 80 weeks of age [22]. Also, the leg muscles evaluated in this study for color had lower values (L* and a*) relative to Hi-Line Brown’s results, while yellowness (b*) in LB and LW was 3.71–4.81 higher relative to Hi-Line Brown [22]. The darker color of the meat in our study is most likely related to the amount of myoglobin in the muscles, which depends on the birds’ genotype, age and physical activity. Myoglobin content in the muscles of young birds is lower compared to older birds and increases with physical activity. This was confirmed in another study by Vargas-Ramella et al. [11] in which high levels of leg muscle yellowness (b*) were also obtained in Isa Brown (b*—13.03) at 72 weeks of age. High levels of muscle yellowness (b*) are influenced not only by the age of the birds but also by nutrition or the maintenance system [23,24]. The muscles of birds that were kept outdoors had more yellow-colored meat than those of birds kept indoors [25]. This was also confirmed in other studies, which showed that birds kept in an open system that fed on carotenoid-rich vegetation had meat that was more yellow than birds kept indoors [23]. In our study, we also noted significant differences in breast and leg muscle color not depending on genotype. LB and LW leg muscles after laying were characterized by significantly (p < 0.05) lower lightness (L*) and higher levels of yellowness (b*) and redness (a*) compared to pectoral muscles. Our results were confirmed in previous studies [11,22,26]. In our study, the genotype of birds did not significantly affect the pH₂₄ value of pectoral and leg muscles. On the other hand, we showed significant (p < 0.05) differences between the acidity reaction of pectoral muscles and pH₂₄ of leg muscles regardless of genotype. Leg muscles had a higher pH₂₄ (0.14–0.17) compared to pectoral muscles. This indicates that the leg muscles performed more physical activity in comparison to the pectoral muscles, resulting in higher levels of myoglobin in the muscles, which influenced the color characteristics analyzed. Also, in another experiment, the acidity of leg muscles was higher than the pH₂₄ of pectoral muscles [11]. In a study conducted by Vargas-Ramella et al. [11], the pH₂₄ of Isa Brown’s pectoral muscles (72 wks) was 5.88, while in an experiment conducted by Lambertz et al. [27] on dual-purpose chicken (75 weeks), it was 5.81–5.83. The obtained results of pH₂₄ of pectoral muscles in the above studies are lower than in our study (LB, BM—5.99). Regardless, the obtained results of the acidity of the pectoral muscles and leg muscles are within the limits (5.90–6.20) of meat suitable for technological processes [26]. An important characteristic for assessing meat quality is EC₂₄. The value of EC₂₄ of meat and byproducts is influenced by the composition of the meat and the compactness of the fat, but also the direction of the muscle fibers [28]. A study by Czyżak-Runowska et al. [29] showed that a decrease in EC values at 24 h after slaughter compared to EC90’ may indicate greater leakage and lower water absorption of the meat, which greatly affects juiciness and tenderness. In our study, the genotype of the birds did not significantly affect the EC₂₄ of the pectoral muscles, while it differentiated the birds in terms of the electroconductivity of the leg muscles. The EC₂₄ value of leg muscles was higher in LB by 1.1 (mS/cm) compared to LW. The reported EC₂₄ results of the pectoral muscle in our study were similar to those in other works [26,30]. In contrast, in the study conducted by Biegniewska et al. [30], the EC₂₄ of leg muscles (6.3–6.8 mS/cm) in Ross 308 at 64 weeks of age was significantly lower than the results obtained in our study (9.7–10.8 mS/cm).

Poultry meat, especially breast muscle, is a rich source of protein which is highly dependent on genotype, breed, age, housing system and nutrition [20]. In our study, the genotype of birds significantly (p < 0.05) affected the percentage of intramuscular fat in breast muscle and the water, protein and intramuscular fat content of leg muscles. An important factor determining the processability of poultry meat is its protein content, its composition and the amount of fat. A study by Puchała et al. [14] showed that the genotype of laying hens significantly influenced the protein and fat content of pectoral muscle and leg muscle fat. In our study, the protein level in the breast muscle (LB—25.2%) was higher than that of Greenleg Partridge (Z11strain—24.73%) [31] and 0.53% lower than that of Isa Brown (25.73%) [11]. In contrast, the percentage of fat in the pectoral muscle in Lohmann Brown was 0.29% lower than Greenleg Partridge and 0.62% lower than Isa Brown. The protein content of leg muscle in the above studies was, similarly to our results, not dependent on genotype (LB, LW), while a significantly higher level of fat was shown in our study (LW—9.9%) than in Rhode Island Red hens (6.15%) [14]. In contrast, another study showed significantly higher levels of protein (22.05%) and lower levels of fat (2.6%) in the leg muscles of Isa Brown laying hens at 72 weeks of age [11]. Based on the results obtained in our study, it can be concluded that LB pectoral muscles with higher fat levels will be more tender and juicier. In our study, the percentage of water in the pectoral muscle regardless of genotype was at a similar level and the results obtained were similar to those in other works [11]. In contrast, the percentage of water in the leg muscle in our study (LW—67.5%) was considerably lower than that of Isa Brown (74.4%) [11]. Poultry meat contains a relatively small amount of collagen, which is a major component of connective tissue [31]. The percentage of collagen in pectoral muscles is about 2.5%, while in leg muscles it is about 6%, which decreases with bird age in pectoral muscles and increases in leg muscles [20]. In our study, we found no significant differences between collagen levels according to genotype. However, the collagen content of leg muscles was significantly (p < 0.05) higher than that of pectoral muscle as evidenced by the p-value (p < 0.001).

In the course of comparing two genotypes of laying hens, we performed a comparative analysis of micro- and macronutrient content in pectoral and leg muscle. Genotype differentiated birds in terms of phosphorus (P) content in leg muscles and iron (Fe) and zinc (Zn) content in pectoral muscle. LB leg muscles contained significantly more (p < 0.05) (44.1 mg/100 g) meat P than LW leg muscles. In a study by Kokoszynski et al. [10], the phosphorus content of leg muscle was significantly lower in Ross 308 (64 weeks) than in our study. In our study, pectoral and leg muscles contained the most phosphorus and potassium. This was also confirmed in other studies, which showed that P and K are the main minerals found in poultry muscle [22,32,33,34]. On the other hand, Kokoszyński et al. [10] showed that there was significantly less phosphorus potassium and zinc in the leg muscles of broiler chickens than in parental flocks of the same genotype. According to Chen et al. [22], the daily requirement of potassium in the human diet is 1500 mg, so it can be assumed that 100 g of breast or leg meat fills the daily requirement at 20%. In our study, we also examined the content of individual micronutrients. Among the most important, we can count iron (Fe) and zinc (Zn), which were higher than the content of copper, manganese or chromium in the analyzed muscles. In another study on Ross 308, the iron and zinc contents were equally high [10]. In our study, significantly more iron, zinc, copper and manganese were contained in leg muscles relative to pectoral muscles regardless of the birds’ genotype. The same relationships have also been shown in other works [10,22,35,36]. Kokoszynski et al. [10] showed that there was significantly more zinc in the leg muscles of parental flocks than in the compared leg muscles of broiler chickens of the same genotype (Ross 308).

Analyzing the muscles of post-reproductive laying hens for sensory evaluation, we showed that LW leg muscles were characterized by inferior tenderness and juiciness compared to LB leg muscles. In contrast, the LB pectoral muscles evaluated were characterized by better juiciness and worse desirability compared to LW pectoral muscles. A study by Kokoszyński et al. [10] showed that the breast and leg muscles of Ross 308 parent flocks (64 weeks) were characterized by inferior sensory evaluation results (juiciness, tenderness and palatability) relative to Ross 308 comparison broiler chickens. Also, in another study, it was shown that the age of birds affected the toughness, juiciness, flavor intensity and palatability of breast muscles [37]. Breast muscles of hens after reproductive age (68 weeks) had higher toughness and lower juiciness, flavor intensity and palatability when compared to breast muscles of broiler chickens [37]. Other authors have confirmed that the age of the birds affects the sensory characteristics of the meat, particularly juiciness, which decreases when the birds are between 9 and 16 weeks of age, while flavor intensity is inversely correlated and increases with age [21].

Many authors have shown that the textural characteristics of the pectoral muscle are influenced by genotype, age of the birds, sex, nutrition and handling of carcasses after slaughter [11,26,38,39]. In our study, the genotype of the birds did not significantly affect the texture characteristics of the pectoralis major muscle. The shear force value (LB—70.0 N) was significantly higher than in our earlier study of Ross 308 (60.2 N) and Cobb 500 (48.1 N) broiler breeders [26]. The higher shear force values in laying hens obtained in our study compared to the parent flocks of meat hens are most likely due to the chemical composition, in particular, the amount of intramuscular fat, which is more abundant in the pectoral muscle in the parent flocks of meat hens. In contrast, other works have shown that the genotype of birds influenced the value of cutting force [26,40]. Most likely, the shear force results obtained in our study were influenced by the age of the birds because with age, the diameter of the muscle fibers increases and there is more connective tissue in the muscles, which affects their hardness [41,42]. A study by Kokoszyński et al. [35] showed lower WB shear force values of pectoral muscles of 42-day-old Ross 308 (20.8 N) and Cobb 500 (24.3 N) broiler chickens. Breast muscle hardness in our study was 2.5 N higher in LW compared to LB. However, our results were higher (LW—35.4 N) than in our earlier study (Cobb 500—28.2 N) [26]. Also, another study showed significantly lower values for the hardness of the pectoralis major muscle in 42-day-old broiler chickens (Cobb 500—15.4 N) [35]. The lower hardness of the pectoral muscles in broiler chickens and parent flocks is due to the size of the muscle fibers and the thickness of the connective tissue, which are significantly lower in younger birds. Other authors have shown that the texture characteristics of the pectoral muscle (tenderness and chewiness) were affected by the age of the birds [43,44]. In contrast, yet other work showed that a varied diet affected the hardness, elasticity, gumminess and chewiness of the pectoral muscle in Isa Brown [11]. In our study, there was no significant effect (p < 0.05) of genotype on rheological properties. But despite this, the sum of elastic moduli and the sum of viscosity moduli of the pectoralis major muscle in LB was higher than in LW (by 23.7 kPa, and by 289 kPa × s, respectively). Another study [35] also showed no effect of genotype on rheological properties but the difference in viscosity and elasticity between Ross 308 and Cobb 500 females at 42 days of age was 31 kPa and 941 kPa × s, respectively.

5. Conclusions

In conclusion, it can be said that Lohmann Brown and Lohmann White’s pectoral muscles are characterized by high protein content and low intramuscular fat content compared to leg muscles. In contrast, leg muscles contained more iron, zinc, copper, manganese, sodium and calcium compared to pectoral muscles. However, more magnesium was found in pectoral muscle. Analysis of textural traits indicated that Lohmann Brown’s pectoral muscle showed more springiness and less gumminess, and less cutting force was needed, compared to Lohmann White. In terms of sensory evaluation, the pectoral muscles were more succulent and the leg muscles were juicier and more tender compared to the LW muscles. Leg muscles were characterized by better tastiness desirability and aroma intensity independent of genotype. Based on these results, it can be concluded that meat from hens after the laying period can serve as material for further technological processing.