Possibilities of Quality Management of Chicken Meat Produced in Polish Industrial Conditions Using an Own-Construction Device for Poultry Electric Stunning in a Water Bath

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Both scientists and meat producers interested in managing the quality of fresh and stored chicken meat at the slaughter stage (as per Directive 1099/2009) are the target audience for this work. The research is innovative in nature and focuses on assessing the possibilities of shaping the visual and technological characteristics of fillets in Polish poultry plants, as expected by consumers, using an own-construction device for stunning poultry in a water bath. The authors demonstrated that the patented device significantly improves meat quality, reducing hemorrhages by approx. 50% and ensuring uniform color and tenderness when compared to commercial devices (Polish, Danish, and Dutch). This improvement could serve as a foundation for producers to implement preventive measures to enhance meat quality management.

Abstract

The aim of the research was to determine the possibilities for managing chicken meat (fillet) quality by applying the own-construction (OC) device for electrical stunning. We determined the effects based on selected technological and visual features of fillets, providing a measurable basis for producers to take preventive actions to improve meat quality management practices. The experimental material consisted of fillets from broiler chickens. The process of electrically stunning chickens in a water bath was carried out in Polish industrial conditions using two devices: own-construction (OC) and commercial from a Polish company (PLC). We determined the quality of fresh and stored meat (14 days/4 °C) based on technological characteristics (pH, color, tenderness) and visual assessment (number of small and large hemorrhages, defects). As a result, the use of the own-construction (OC) device compared to the commercial (PLC) one has a beneficial effect on: (1) reducing the number of hemorrhages, (2) increasing the share of high-quality fillet production by approx. 50%, (3) brightening and uniforming the color of fillets, and (4) improving the tenderness of fresh meat and maintaining it during 14 days of storage. The effects of using the OC device are beneficial for meat producers on the market.

1. Introduction

Quality is an interdisciplinary term, and its perception depends on what it concerns and by whom it is assessed. One can perceive quality from the following perspectives: objective—focused on the quality of the product, process, control; and subjective—customer oriented. When keen to satisfy food quality attributes, it is important to consider customer requirements and expectations. Food processing facilities wishing to maintain high product quality should focus on continuous improvement and search for reasons for deviations from the planned results in the existing production system to take actions aimed at minimizing negative effects and maximizing the use of emerging opportunities [1]. Polish poultry production, which has maintained its leading position among European Union countries since 2014, engages in such activities. The Polish poultry industry has set several strategic goals to achieve by 2024. These goals include maintaining a high level of poultry consumption in Poland by building values such as quality, safety, and sustainable production of meat and poultry products. Moreover, scientific research and development work are conducted to improve the quality of poultry meat [2].

The process of stunning poultry is the first and most important technological process, which, while ensuring humane behavior during slaughter (depriving the birds of consciousness and feeling until bleeding), determines the good quality of meat and carcasses. The most popular method in Poland and most countries in the world is the method of electric stunning in a water bath [3,4,5]. It is often criticized due to animal welfare during slaughter and reduced meat quality, which generates large economic losses. To ensure the effective stunning of poultry, the legislative document developed [6] strictly indicates defined doses of electric current, characterized by a range of frequency and intensity values. To achieve effective stunning in 90% of chickens, the minimum current per animal was determined: at frequency (f) < 200 Hz—100 mA; at f = 200–400 Hz—150 mA; and at f > 400 to 1500 Hz—200 mA. In practice, however, it turned out that the variants of electrical parameters suggested in the current Regulation (much higher than before the entry into force of this Regulation) do not allow maintaining high quality standards and cause more hemorrhages in fillets [7,8,9]. Meat defects in the form of hemorrhages are noticeable, especially on the inside of fillets sold both loosely and in packages, so they significantly reduce their culinary and technological usefulness, reduce customer purchasing decisions, and lower the market price of meat [10,11]. The results of own research on the effects of using own-construction devices for stunning poultry compared to commercial devices (Dutch and Danish companies), most often used in poultry plants, showed that the current parameters used [12,13] allow for an increase of approx. 50% of the production of high-quality fillets without hemorrhages and with uniform color [14,15], which also meet the expectations of Polish consumers [10]. The availability of devices for electrically stunning poultry on the domestic market and their use by Polish plants inspired the authors to continue the research problem with a broader scope of analysis and evaluation.

The aim of the research was to determine the possibility of managing the quality of chicken meat, fresh and refrigerated, using two stunning devices—own-construction and a commercial one from a Polish company (control). These possibilities were determined on the basis of instrumental assessment of technological parameters (pH, tenderness, color, cooking loss) and visual features (hemorrhages, defects) of meat, as well as Profit statistical analysis, which constitutes measurable evidence for producers to take actions to improve the production process and meat quality.

2. Materials and Methods

The research was carried out in industrial conditions at a poultry plant in the central-eastern part of Poland. The experimental material consisted of fillets of broiler chickens of the Ross breed, approx. 6 weeks old, whose average live carcass weights were between 1.60 and 2.10 kg. Live birds were delivered to the slaughterhouse from a farm approx. 100 km away from the plant by road. The plant assessed the raw material as having good quality based on its adopted criteria. The experimental slaughter process—using own-construction (OC) and commercial (PLC) devices—was carried out on approximately 1000 live birds (of the same batch, from the same flock) in accordance with the requirements of humane slaughter [6]. Experimental stunning procedures were carried out by employees of the poultry plant with the appropriate level of qualifications to perform activities related to slaughter. A sufficient degree of animal stunning has been confirmed by a veterinarian based on his competence and subjective visual assessment. The production line was able to produce 6000 pieces per hour. The broiler stunning process was carried out using an electric method in a water bath, using two devices:

⮚

own-construction (OC) [12,13]: rectangular wave AC, f = 400 Hz, U = 100 V,

⮚

commercial, Polish company (PLC): sine wave AC, f = 200 Hz, U = 120 V.

Moreover, the OC stunning method did not subject the live birds to any conditions that are different from other commonly practiced methods.

The process of experimental and control stunning of broilers was carried out with 5 min breaks between trials.

On a cooled batch of experimental and control carcasses (air method with water spray, 2 °C/2 h), industrial cutting into portions, including fillets, was carried out (without cleaning). One hundred pieces of left fillets were randomly taken from the obtained experimental (OC) and control (PLC) meat. The assessment of the impact of the broiler stunning devices on meat quality was carried out on fresh fillets (approx. 9 h after slaughter), vacuum packed and stored in polyethylene bags for 7, 9, 12, and 14 days in a cooling chamber (temp. 4 ± 0.1 °C, Memmert ICP 500, Schwabach, Germany).

2.1. Visual Assessment of the Number of Hemorrhages and Defects

The visual assessment of fresh meat (left fillets), in terms of the frequency and number of petechiae (hemorrhages), was carried out by a trained five-person committee. Criteria for the quantitative assessment of the occurrence of hematomas and defects were developed by Banach [14], taking into account quality problems suggested by the manufacturer. The subject of the fillet quality assessment was hemorrhages occurring in/on the fillet on the outside and inside, with hemorrhages of various sizes (small, ø < 10 mm; large, ø > 10 mm)—Figure 1. The number of present hemorrhages determined the defectiveness of the meat. The assumption that even one hemorrhage, regardless of size, classified the fillet as a defective product was the basis for this assessment criterion.

2.2. Color Measurements

The Hunter Miniscan XE Plus colorimeter (HunterLab, Reston, VA, USA) was used to measure the color of randomly chosen fillets. It was set to collect spectral data with illuminant A/observer D65/10° on the CIELAB scale (L*, a*, b*). Before starting the measurements, the device was calibrated using ceramic reference plates (white and black). Color measurements were performed on fresh meat (approx. 9 h after slaughter, n = 30) and refrigerated meat (7, 9, 12, and 14 days, air temperature approx. 2 °C, n = 6), in 3 repetitions for each sample. Additionally, when assessing the color of the meat, two elements were taken into account: the tenderloin (m.pectoralis minor—MPn) and the fillet (m.pectoralis major—MPj), including the external surface (ES) and the internal surface (IS). To increase the objectivity of the assessment, places with visible defects (e.g., hemorrhages) were omitted during the measurements. Figure 2 shows a visualization of the different colors of the fillets in terms of brightness (L* parameter).

2.3. pH Measurements

pH measurements of experimental and control samples (fresh, n = 30 and stored, n = 6) were performed using a CP-411 pH meter equipped with an FC 200 dagger electrode (Elmetron, Zabrze, Poland) in the thickest part of the fillet (m. pectoralis major—PMj) in 3 repetitions for each trial. Measurements were taken approx. 9 h after slaughter, and after 7, 9, 12, and 14 days of storage. Before starting the tests, the pH meter was calibrated with two buffers (pH 4.0 and 7.0) and washed with distilled water.

2.4. Texture Measurements

Texture tests were carried out on fillets (approx. 300 g) after heat treatment in a water bath (80 °C/15 min, WB14-Memmert GmbH + Co., KG, Schwabach, Germany). Test samples were cut from the thickest part of the fillet in the shape of a cuboid (30 × 10 × 30 mm). Instrumental evaluation of meat texture was carried out using an Instron device (type 5942, Instron Corp., Norwood, MA, USA) and a piercing test (pin, ø = 11.32 mm, speed of working elements 50 mm/min). Measurements of the maximum puncture force (F_p) and deformation during puncture (D_p) were performed in 8 repetitions for each test at an ambient temperature of approximately 20 °C. The results were analyzed using a computer with Bluehill^®2 Software ver.2.1 (Norwood, MA, USA).

2.5. Cooking Loss

Meat weight loss after heat treatment was determined based on the following formula [16]:

Cooking loss [%] = (a − b)/a × 100

where: a—mass of the meat sample before pasteurization [g], b—mass of the meat sample after pasteurization [g]

2.6. Statistical Analysis

The obtained results were subjected to statistical analysis using the Statistica v.13.1 program. The characteristics of the studied variables were determined (arithmetic mean, standard deviation, variance), and the strength and direction of the relationship between the analyzed objects (device; storage time) and meat parameters were identified at the level of significance of differences (p < 0.05; p < 0.01). Then, PROFIT analysis was performed, which allows for vector scaling (non-linear reduction of dimensionality) and multiple regression analysis [17]. The aim of this analysis was to check the impact of the device used (OC, PLC) and storage time (fresh, 7–14 d) on the assessment of similarities between a set of parameters characterizing meat quality (hemorrhages, pH, F_p, D_p, cooking loss). In the first stage of extended multidimensional scaling, the configuration of points in two-dimensional space was obtained. In the second stage of the Profit analysis, multiple regression was determined using coordinates (independent and dependent variables), presented in the form of a biplot.

3. Results and Discussion

3.1. Assessment of the Quality of Fresh Fillets

The results of the visual assessment of hemorrhages in chicken fillets showed that the use of an own-construction (OC) device significantly (p < 0.01) reduced the number of small hemorrhages on the external surface (2 times) and large and small hemorrhages on the internal surface of the fillet (approx. 2.5 and 3.5 times, respectively) compared to the number of hemorrhages in chicken fillets stunned using the PLC device. A much larger number of small hemorrhages (external and internal) occurring in the meat of chickens stunned with PLC may result from an inappropriate selection of the current frequency, which results in an increase in pressure in the blood vessels and capillaries in stressed birds, causing their rupture and, consequently, blood leaking into the surrounding tissues [18,19].

A significant (p < 0.01) effect of the OC device on the number of hemorrhages in fillets was also confirmed by statistical analysis (Figure 3A). The results of the assessment of fillet defects (Figure 3B) also showed that the use of the OC device allows the production of fillets without defects at a level of approximately 60%, while when using a commercial device (PLC), the production of meat without defects was only 15%.

The obtained results confirm the research previously carried out by the authors on the beneficial effect of the own-construction device on the production of high-quality chicken fillets [20] and the reduction of serious and minor meat defects (approx. 50%) in commercial elements of turkey carcasses—fillet, loin, and wing [14,15] compared to defects occurring using equipment from the Netherlands and Denmark. According to Mouchoniere et al. [21,22], at a higher current frequency (800 Hz), obtaining a smaller number of defects is the result of more effective stunning, i.e., faster and longer loss of consciousness in all birds, which consequently allows for better bleeding and the occurrence of fewer hemorrhages. The use of electric current with a frequency of 400 Hz in the stunning process results in a slightly higher defect of meat than in the case of f = 800 Hz.

The results of measuring the pH of fresh meat (pH_9h) revealed that the type of device (OC and PLC) and its parameters did not significantly affect the meat’s pH, as their values remained at a similar level of approximately 5.90 (

Table 1. The values (mean ± standard deviation) of pH_9h, maximum puncture force (F_p), deformation (D_p), and cooking loss from meat of chickens stunned using the own-construction (OC) and Polish company (PLC) devices.

Measured Parameter	Type of Device
	OC	PLC
pH9h	5.88 ± 0.11	5.90 ± 0.07
Fp [N]	25.44 ± 4.31 A	27.82 ± 2.35 B
Dp [mm]	7.88 ± 0.76 A	9.32 ± 1.73 B
Cooking loss [%]	14.75 ± 1.62	15.06 ± 0.55

^A–B—significant differences between rows (devices), p < 0.05.

). Taking into account the division into meat quality classes adopted in the literature on the subject, this meat should be considered of good quality (so-called normal, pH = 5.9–6.2). Despite the lack of differences between the pH values of fresh meat, a significant (p < 0.05) effect of the type of device was observed in meat tenderness, determined using the instrumental method. The results of measurements of the maximum puncture force (F_p) and deformation (D_p) of fillets from chickens stunned using a PLC device showed that their values were on average 27.82 N and 9.32 mm and were higher by approximately 9% and 18% than the values of F_p and D_p of fillets from chickens stunned using an OC device. We observed a similar relationship, albeit not statistically significant, in the case of cooking loss. As a result of using the PLC device, its average value was approximately 15% and was approximately 2% higher than the value of cooking loss from fillets from chickens stunned using OC (Table 1). This proves the better tenderness and greater juiciness of chicken fillets stunned using the OC device than meat produced using the PLC device.

The results of measurement of the parameters (L*, a*, b*) of the color of fresh fillets showed that the L* values of the color of the external (ES) and internal (IS) surfaces of the m. pectoralis major (PMj) and m. pectoralis minor (PMn) muscles from chickens stunned using the OC device were, respectively, approx. 67, 63, and 58, and were higher than the L* values of the corresponding muscles of chickens stunned with the PLC device by approx. 2.5%, 2%, and 2%. The a* ES and IS values of the above-mentioned muscles of chickens stunned with the OC device were 2.94, 3.19, and 4.22, respectively, and were smaller than the a* of the corresponding muscles of chickens stunned with the PLC device by approx. 9%, 5%, and 8%. The b* values of ES and IS—PMj colors of chickens stunned with the OC device were 12.41 and 15.81, respectively, and were higher than the b* values of this muscle of chickens stunned with the PLC device by approximately 8.4% and 4.6%. The b* value of the PMn color of chickens stunned using the OC and PLC devices was the same—15.12 (

Table 2. The values (mean + standard deviation) of color parameters L*, a*, b* of fresh meat produced using devices for electrical stunning of chickens—own-construction (OC) and a Polish company (PLC).

Type of Device	m.pectoralis major (PMj)		m.pectoralis minor (PMn)	Analysis of Variance, Variable Surface
	External Surface (ES)	Internal Surface (IS)
				ES-IS	IS-PMn	PMn-ES
L*
OC	66.92 ± 2.39 b	62.86 ± 2.50	58.18 ± 2.36 B	**	**	**
PLC	65.35 ± 1.96 a	61.88 ± 1.91	56.97 ± 1.99 A	**	**	**
a*
OC	2.94 ± 0.96	3.19 ± 0.90	4.22 ± 0.78	NS	**	**
PLC	3.23 ± 0.69	3.36 ± 0.77	4.59 ± 1.08	NS	**	**
b*
OC	12.41 ± 1.27 b	15.81 ± 0.92 b	15.12 ± 1.20	**	**	**
PLC	11.45 ± 1.06 a	15.12 ± 0.85 a	15.12 ± 1.20	**	NS	**

^a–b—significant differences between rows, p < 0.01; ^A–B—significant differences between rows, p < 0.05; **—significant differences between surfaces, p < 0.01; NS—no significant differences.

).

The results of color parameter measurements clearly indicate that the use of the OC device results in greater meat brightness (L* ≈ 67–58), and low values of the a* parameter—red color saturation (2.94–4.22) and high values of the b* parameter—yellow color saturation (12.41–15.12), which are probably the result of a smaller number of hemorrhages occurring on the inner and outer surfaces (Figure 3A) and defects (Figure 3B). Statistical analysis of chicken meat color parameters showed significant differences (p < 0.01; p < 0.05) between the L* of ES color of fillet and tenderloin of chickens stunned using the OC and PLC devices. Significant differences (p < 0.01) were also observed between the b* color parameter of chicken fillets stunned with OC and PLC devices (Table 2).

The conducted research shows that, regardless of the stunning device used, the L* values of the color of the fillet on the external surface were higher and differed significantly from the L* value of the color on the internal surface of the fillet and tenderloin. The obtained results confirm the results of research by Sandusky and Heath [23] and Wilkins et al. [24], where the outer surface of the fillet was lighter than the internal surface. Therefore, measuring the color on the external surface may pose a problem when classifying the raw material into a specific quality group [25]. Moreover, it is difficult to determine the quality of meat based on the L* value because studies conducted by various researchers have shown a wide range of values for this parameter, e.g., 45–67 [24], 41–66 [26], 43–56 [27], and 55–62 [28].

3.2. Assessment of Technological Quality of Stored Meat

Chilled meat will be the basic form of selling meat products in the future, so it is important to guarantee high-quality meat already at the stage of slaughtering animals and then during storage [29]. The ability to manage the quality of chilled meat in segments of the processing chain and customer deliveries [11] will allow for sustainable management of the production of packaged meat. Therefore, the study aimed to assess the technological suitability of refrigerated meat storage, considering changes in pH, tenderness, cooking loss, and color.

The results of meat pH measurements during storage revealed that the use of the OC device had an insignificant effect on the meat’s pH values, which varied in the range of 5.90–6.00. When the PLC device was used, significant changes (p < 0.05) in the pH of the meat during storage were observed. For 12 days of storage, the pH values increased in the range of 5.90–6.08, then on the 14th day they decreased to 5.88. An analysis of the impact of the type of appliance used revealed that this factor differentially affects the pH of meat in the final storage period (12 and 14 days). The observed trends testify to the beneficial effect of the OC device on the quality of meat, while a decrease in the pH value to 5.88 in the final period of its storage (

Table 3. Changes in values (mean ± standard deviation) of pH, maximum puncture force (F_p), deformation (D_p), and cooking loss, from meat of chickens stunned using the own-construction (OC) and Polish company (PLC) devices during 14 days of storage.

Time of Storage [Days]	Type of Device	pH	Fp [N]	Dp [mm]	Cooking Loss [%]
7	OC	5.86 ± 0.02	22.96 ± 5.21 A	8.50 ± 0.58 a	12.91 ± 0.68
	PLC	5.81 ± 0.06	27.82 ± 7.28 B	9.92 ± 1.14 b	13.44 ± 0.11
9	OC	5.92 ± 0.12	21.94 ± 2.95	8.02 ± 1.28	17.76 ± 3.64
	PLC	6.08 ± 0.10	20.95 ± 3.51	7.55 ± 1.29	17.13 ± 1.42
12	OC	5.92 ± 0.10 a	22.65 ± 3.24	8.26 ± 1.05	17.69 ± 2.85
	PLC	6.16 ± 0.13 b	22.55 ± 2.68	8.50 ± 0.98	19.83 ± 0.48
14	OC	6.00 ± 0.06 b	22.89 ± 3.27	8.19 ±1.26	17.43 ± 0.55
	PLC	5.88 ± 0.09 a	22.75 ± 2.93	8.20 ± 1.04	14.95 ± 1.84
Analysis of variance, variable storage time	OC	NS	NS	NS	NS
	PLC	*	**	**	*

^a–b—significant differences between rows (devices), p < 0.01, ^A–B—significant differences between rows, p < 0.05; **—significant differences, p < 0.01; *—significant differences, p < 0.05, NS—no significant differences.

), in the case of the use of the PLC device, may indicate the process of protein denaturation already taking place in meat [30]. To identify the direction of changes occurring in the meat during storage, an instrumental fragility assessment was carried out, which is a function of the biochemical properties of the muscles in the time after slaughter and the rate and severity of the development of post-mortem concentration [31].

The meat tenderness tests showed that the maximum puncture force (F_p) of the fillets of chickens stunned using the OC device dropped to about 23 N after 7 days of storage compared to fresh meat (Table 1). The F_p value of the fillets of chickens stunned using the PLC device stayed the same at about 28 N. After 9 days of storage, the F_p value of the fillets of chickens stunned using the OC device was approx. 22 N, and the F_p value of the fillets using the PLC device decreased to approx. 21 N. During 12 to 14 days of storage, F_p values, regardless of the type of device, were at a similar level of approx. 23 N. Statistical analysis of the influence of meat storage time on changes in F_p values revealed significant differences (p < 0.05) only in the case of stunning chicken fillets using a PLC device. The deformation values (D_p) of chicken fillets stunned using the OC device were, similarly to the F_p values, at a similar level (8.50–8.02 mm) throughout the entire storage period, and did not differ significantly. The D_p values of chicken fillets that were stunned using the PLC device and stored for 7 and 9 days were 9.92 and 7.55 mm, respectively. After 12 days of storage, they increased to 8.50 mm, and after 14 days, they decreased to 8.20 mm. Statistical analysis of the influence of the storage time of meat from chickens stunned using a PLC device on changes in D_p showed, similarly to F_p, significant differences at the p < 0.01 level. The type of device used (OC/PLC) had a significant effect (p < 0.01) on the variation in the D_p value of the fillet stored for 7 days (Table 3).

A significant (p < 0.05) reduction in the F_p value may be caused by the initiation of proteolytic processes and the release of amino acids, which also reduce the pH of meat [32]. However, the lack of significant changes in F_p and D_p during 14 days of storage proves the beneficial effect of the OC device on meat tenderness (maturity), which is one of the most important quality determinants for the consumer. By maintaining their native structure, myofibrillar proteins retain their water-holding capacity, providing more desirable textural properties [33]. According to Banach [14], structural changes in muscle tissue and meat tenderness are influenced by the frequency of electric current flowing through the chicken body during stunning. As the current frequency (f) increases, cell membranes lose their impermeable properties, and the current flows through both intracellular and extracellular spaces. At f = 800 Hz, the current flows evenly through the bird’s entire body, causing degradation of the muscle tissue structure to the same extent. The beneficial effect of high current frequencies (480, 600, and 750 Hz) compared to low frequencies (f = 50 Hz) on improving meat tenderness was also demonstrated by Sante et al. [34] and Huang et al. [9]. The authors described its beneficial effects as a significantly higher myofibril fragmentation index and lower glycogen content in muscles after slaughter.

Although cooking losses are an important indicator of the meat’s water-holding capacity during thermal processing, the test results showed that the values of cooking loss from chicken meat stunned using the OC and PLC devices did not differ significantly at any stage of storage. Nevertheless, these changes in the meat of chickens stunned with the PLC device differed significantly (p < 0.05) as a function of storage time, which also confirms the significance of changes in the pH parameters (p < 0.05) and tenderness F_d and D_p (p < 0.01)—Table 3.

Taking into account that when assessing the quality of packaged meat, the consumer pays mainly attention to the color or its variation in the individual packaging [35], if the color is not acceptable, all other quality characteristics lose their importance; therefore, the influence of an additional factor of storage time (apart from the type of device) on the color changes of fillets and tenderloin was determined.

The results of measurements of the color of meat stored for 7, 9, 12, and 14 days showed that the values of the L* parameter of the color of the external surface (ES) of fillet (PMj) of chickens stunned using the OC device were, respectively: 65.25, 67.99, 68.40, and 62.06, while on the internal surface (IS), they were smaller, respectively, and amounted to: 63.10, 64.98, 66.30, and 61.78. The L* values of the tenderloin (PMn) during the storage time presented above were lower than the values on the IS surface, which were: 60.48, 61.97, 62.19, and 59.51. The values of the ES color parameters a* and b* of the fillet and tenderloin of chickens stunned with OC and stored for 7, 9, 12, and 14 days were, respectively: 2.76, 3.19, 3.24, and 3.96; and 15.53, 14.64, 15.25, and 13.83. The a* and b* values of the IS color of the fillet (except for the a* value of the muscle stored for 7 days) were higher and amounted to, respectively, 2.63, 3.77, 3.67, 4.16 and 17.30, 16.04, 16.99, and 16.29. The a* and b* values of the tenderloin color varied and amounted to: 3.28, 3.45, 5.20, 4.58; and 16.52, 14.43, 16.92, and 15.31. The results of previous own research [28] showed a beneficial effect of the device of own-construction compared to the effect of the Meyn device, expressed in a more even and stable color during storage, regardless of the time and origin of the raw material (

Table 4. Changes in the values (mean + standard deviation) of the color parameters L*, a*, b* of chicken fillets electrically stunned using own-construction (OC) and commercial—Polish company (PLC) devices, during 7, 9, 12, and 14 days of storage.

Time of Storage [Days]	Type of Device	m.pectoralis major (PMj)						m.pectoralis minor (PMn)
		External Surface—ES			Internal Surface—IS
		L*	a*	b*	L*	a*	b*	L*	a*	b*
7	OC	65.25 ± 1.31	2.76 ± 0.44	15.53 ± 1.47	63.10 ± 0.61	2.63 ± 1.36	17.30 ± 1.99	60.48 ± 1.75	3.28 ± 1.54	16.52 ± 1.62
	PLC	65.54 ± 2.33	3.16 ± 0.55	14.53 ± 0.93	63.90 ± 2.92	3.83 ± 0.38	17.27 ± 0.88	60.75 ± 2.10	4.59 ± 0.32	16.64 ± 1.21
9	OC	67.99 ± 1.45	3.19 ± 0.42	14.64 ± 0.96 b	64.98 ± 1.57	3.77 ± 0.52	16.04 ± 0.70 B	61.97 ± 0.50 B	3.45 ± 0.68	14.43 ± 0.71 b
	PLC	63.76 ± 6.45	3.64 ± 1.53	11.71 ± 1.66 a	62.42 ± 5.04	4.19 ± 1.43	14.53 ± 1.30 A	58.18 ± 3.93 A	4.47 ± 2.38	13.14 ± 0.59 a
12	OC	68.40 ± 1.04 b	3.24 ± 0.98	15.25 ± 1.42 B	66.30 ± 2.55 b	3.67 ± 0.75	16.99 ± 1.49	62.19 ± 0.51 b	5.20 ± 1.66	16.92 ± 1.66
	PLC	63.07 ± 3.47 a	3.86 ± 1.09	12.98 ± 1.83 A	61.42 ± 1.32 a	4.24 ± 0.40	16.01 ± 0.84	58.89 ± 0.94 a	4.81 ± 0.43	15.48 ± 0.74
14	OC	62.06 ± 1.29	3.96 ± 0.82 A	13.83 ± 0.93	61.78 ± 1.73	4.16 ± 1.37	16.29 ± 0.93	59.51 ± 0.46	4.58 ± 1.24	15.31 ± 1.24
	PLC	62.65 ± 1.76	4.92 ± 0.84 B	14.60 ± 2.03	61.60 ± 2.15	4.35 ± 0.73	17.07 ± 1.25	59.18 ± 1.36	5.51 ± 1.43	15.72 ± 0.87
Variance analysis (time of storage)	OC	**	*	NS	**	NS	NS	**	NS	*
	PLC	NS	*	NS	NS	NS	**	NS	NS	**

^a–b—significant differences between devices, p < 0.01; ^A–B—significant differences between rows, p < 0.05; *—significance of differences during storage (p < 0.05); **—significance of differences during storage (p < 0.01). NS—no significant differences.

).

After 7 and 14 days of storage, the values of the ES color parameter L* of chicken fillets stunned with PLC were higher (by 0.44% and 0.9%), and after 9 and 12 days of storage, they were lower (by 6.2% and 7.8%) than the L* values of chicken fillets stunned with the OC device. After 7 days of storage, the L* values of the IS color of fillets and tenderloins of chickens stunned using the same device (PLC) were higher by 1.3% and 4.5%, while after 9, 12, and 14 days of storage, they were lower by 3.9%, 7.4%, and 0.3%, and at 6.11%, 5.3%, and 0.55% of the L* value of these muscles of chickens stunned with the OC device. In the case of the parameter a*, which is the red color saturation on ES and IS of chicken fillets stunned with the PLC device and stored for 7, 9, 12, and 14 days, its values were higher by approximately 14.5%, 14.1%, 19.1%, and 24% and approx. 45.63%, 11.14%, 15.5%, and 4.56% of the a* value of chicken fillets stunned using the OC device (Table 4).

An inverse relationship with changes in the saturation of the red color (a*) was observed with changes in the saturation of the yellow color (b*). The b* values of meat from chickens stunned with the PLC device were lower for: ES of fillets stored for 9 and 12 days by approx. 20 and 15% and IS of fillets stored for 7, 9 and 12 days by approx. 0.2; 9.4 and 5.8% from the b* value of chicken fillets stunned with the OC device. The exceptions were: ES of fillets stored for 7 days—b* values were the same for the OC and PLC devices, and ES and IS of fillets stored for 14 days—b* values were higher by approximately 5.6 and 5.0% for the meat of chickens stunned with the OC device (Table 4).

The a* values of the tenderloin of chickens stunned with the PLC device and stored for 7, 9, and 14 days were higher by approximately 39.94, 29.56, and 20.30%, while when stored for 12 days, they were 7.5% lower than the corresponding a* values of chicken tenderloin stunned using the OC device. The b* values of the color of chicken tenderloin stunned using the PLC device and stored for 7 and 14 days were higher by 0.73 and 2.68%, while those stored for 9 and 12 days were lower by 8.94 and 8.51% compared to the a* value of chicken tenderloin stunned with the OC device (Table 4).

Summarizing the obtained results of color parameter tests and their statistical analysis, it was found that the lightness—L* of the meat color (fillets, tenderloins) of chickens stunned using the OC device was higher than when using the PLC device, and the storage time had a significant effect (p < 0.01) on its changes (Table 4). The greater lightness of the meat color may result from the decreasing water-holding capacity, especially as a result of increasing water loss during thermal processing (Table 4). According to Hayat et al. [30], poor water holding capacity is caused by the presence of more liquid on the surface of the meat, which enhances light reflection. Denaturation of proteins during storage causes light to pass through the meat tissue and changes the way it is scattered compared to the normal refractive behavior of proteins. Significant differences (p < 0.01) between the brightness and saturation of red and yellow meat in chickens stunned with OC and PLC were observed mainly after 9 and 12 days of storage, with an inverse relationship between changes between the values of parameters a* and b*. Significant differences in changes in meat color parameters of chickens stunned using the PLC device were observed only in the case of parameters a* (ES fillet, p < 0.05) and b* (IS fillet, p < 0.01 and tenderloin, p < 0.01). The results of research by other scientists have shown that the saturation of the red color (b*) is influenced by voltage [9,36] and current intensity [7], while the saturation of the yellow color has no significant influence: frequency [37], voltage [36], intensity [7], and the electrical stunning method [9,38]. According to Siqueira et al. [39], in the meat of broilers stunned with a higher current frequency (650 Hz), a higher yellowness value was obtained compared to broilers stunned with a low current frequency (300 Hz).

As a result of the PROFILE analysis—multidimensional scaling and Euclidean distance, eleven features characterizing chicken meat were reduced to two dimensions. As a result of these activities, each of the examined features received two coordinates, thanks to which it was presented in the form of a two-dimensional perception map. The value of the “Stress” coefficient for multidimensional scaling, taking into account all features, was 0.00036; therefore, the scaling procedure was reliable. Parameters of the regression function (b₀, b_Dim.1, b_Dim2), in which the explained variable were meat parameters and the explanatory variables—the values of two dimensions for each object. Based on the obtained values of determination coefficients (R²), it can be concluded that the tested objects (type of device, storage time) significantly affect such quality characteristics as: hemorrhages (LEx, SEx, LIn, SIn), tenderness (F_p, D_p), and color (a*, b*)—

Table 5. Results of regression analysis between meat parameters and the obtained dimensions of the examined quality characteristics (b₀, b_{(Dim. 1)}; b_{(Dim. 2)}).

Parameters	b0	b(Dim. 1)	b(Dim. 2)	R2
Large external (LEx)	3.50 ***	−0.55 ***	0.05 ***	0.99
Large internal (LIn)	20.50 ***	12.62 ***	−1.03 ***	0.99
Small external (SEx)	9.00 ***	3.29 ***	−0.27 ***	0.99
Small internal (SIn)	46.00 ***	36.22 ***	−2.95 ***	0.99
pH	5.94 ***	0.03	0.15	0.29
Fp	23.72 ***	0.53	−4.64 ***	0.76
Dp	8.40 ***	0.32 ***	−1.32 ***	0.85
Cooking loss	16.09 ***	0.03	2.58	0.52
L*	−0.46 *	−0.55	−0.35	0.49
a*	0.16 ***	−0.04	−0.12 *	0.55
b*	−0.20 *	−0.11 **	−0.68 *	0.65

*—p < 0.05; **—p < 0.01; ***—p < 0.001; R²—coefficient of determination.

.

The biplot (Figure 4) presents the location of the meat quality parameters and the tested objects (OC/PLC*storage time) in a multidimensional space. The obtained biplot shows that, taking into account the factors of the OC device for stunning poultry and meat storage time, they have the greatest impact on the occurrence of large hemorrhages on the external surface and the color (L*, a*, and b*), which mainly determine the improvement of the visual characteristics of fillets and can significantly reduce meat (fillet) and economic losses in the poultry plant [14]. However, in the variant of factor analysis (PLC—commercial device) and storage time, their influence on quality characteristics was split into two groups of meat. The greatest impact, in relation to fresh meat and meat stored for 7 days, has large hemorrhages on the internal surface (LInHemor.) and small hemorrhages on its internal and external surfaces (SInHemor, SExHemor)—occurring in the largest number, as well as tenderness parameters (F_p and D_p), indicating greater hardness of meat. In the case of meat stored for 9, 12, and 14 days, the influence of the PLC device (at a lower level) was observed in terms of cooking loss and pH as well as L*, b*, and a* (negative relationship), which changed during storage as a result of protein denaturation.

To sum up, it was stated that the results of the studies and their statistical analysis clearly indicated the aim of taking implementation measures of the self-construction device (OC) and renouncing the Polish construction device (PLC), so that in terms of strategic and operational activities, the plant could manage the quality of the meat produced in it. Despite the beneficial technological effects obtained as a result of the use of the OC device, a valuable supplement to the effectiveness of its impact will be further studies to evaluate animal welfare (physiological and behavioral indicators) during their slaughter.

4. Conclusions

The obtained results of the study demonstrated that using an own-construction (OC) device for stunning poultry, as opposed to a device from a Polish company (PLC), had the following effects: (1) reducing the number of hemorrhages, mainly large ones, that determine the quality and durability of meat, as well as its acceptability or lack thereof by consumers; (2) increasing the share of production of fillets without hemorrhages (without defects) by approx. 50%; (3) brightening and unifying the color of the outer and inner surfaces of the fillet during storage, which consumers pay a lot of attention to when shopping; (4) improving the tenderness of the fillet and maintaining it at a constant level throughout the entire storage period (stability), which proves that it is fully ripe in a much shorter time than fillets from chickens stunned using a PLC device. The obtained effects of improving meat quality prove the possibility of pro-quality management of meat production at the poultry slaughter stage using the OC device for stunning poultry, especially in the face of increasing demand for poultry meat and competition on the domestic and foreign markets.