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Journal of Food Science and Technology logoLink to Journal of Food Science and Technology
. 2022 Mar 4;59(9):3683–3692. doi: 10.1007/s13197-022-05391-7

Air chilling of Turkey carcasses: process efficiency and impact in the meat quality traits

Rosemar Frigotto Saggin 1, Naimara Vieira do Prado 1, Maycon Meier dos Santos 2, Evellin Balbinot-Alfaro 3, Alexandre da Trindade Alfaro 1,✉
PMCID: PMC9304514  PMID: 35875225

Abstract

The study evaluated the influence of two air-spray chilling systems on the water absorption, cooling time, and the impact of both on the quality traits of the turkey meat. In system A (air/water spray + air) a weight loss of 1.78% (w/w) occurred, while in system B (continuous air/water spray) turkey meat showed a weight gain of 1.82 (w/w). The cooling time in system B was significantly (P < 0.05) shorter. Water retention capacity, the color, and the sarcomere length of turkey meat are significantly influenced (P < 0.05) by the air chilling system. Turkey meat refrigerated in system B showed smaller structural changes. Air chilling with water spray in a continuous process promotes carcass weight gain and reduces processing time, in addition to less impact on the quality traits of turkey meat.

Keywords: Chilling process, Poultry meat, Water absorption, Cooling time, Economic losses

Introduction

Turkey meat has gained great popularity around the world and is used in many regional cuisines (Murawska et al. 2015). Turkey meat is lean compared with red meat, being a source of essential components of diets in developed countries, especially for their sensory characteristics, such as taste and texture.

Brazil is a major world producer and exporter of turkey meat. According to the Brazilian Animal Protein Association (ABPA 2019), Europe is one of the main importing continents. Among the parameters required by Europe for the purchase of turkey meat is the control of the percentage of water absorption and the moisture: protein ratio (MPR) of the carcasses.

The parameters must comply with the European Union Implementing Regulation (EU) 1239/2012 (European Commission 2012). According to the regulation, are allowed chilling systems by air, air with water spray, immersion, or even combined chilling systems by two or more of these methods. For any combination of chilling methods, weight gain in the process is not allowed. In the air-spray chilling method, the absorption percentage must be a maximum of 2.0%, while in immersion chilling, the weight gain must not exceed 4.5%.

In poultry processing, effective and proper chilling is a critical factor affecting the overall quality. In poultry processing, effective and proper chilling is a critical factor affecting the overall quality. The purpose of chilling is to reduce the temperature below which pathogens can grow and microbial growth of spoilage organisms is limited. According to Regulation (EC) No 853/2004 of the European Parliament and of the Council, after inspection and evisceration, turkey carcass must be cleaned and refrigerated until they reach a lower temperature to 4 °C as soon as possible (European Commission 2004).

According to Sansawat et al. (2014), air chilling has many advantages, such as reduced water consumption, reduced wastewater, lower labor costs, and the potential for improving product quality. However, air chilling can change the water content of meat and can cause dehydration and discoloration on the surface of the carcasses (Demirok et al. 2013).

The weight loss of the carcass through the change in its water content can result in changes in its physical and chemical characteristics, in addition to significantly impacting the economic viability of the process. In the same way, the cooling time of the carcasses has a direct influence on the cost of the process.

The air chilling system is widely used for cooling turkey carcasses in Brazil and other countries of the world. Therefore, the evaluation of its influence on meat characteristics and carcass weight reduction is essential for processing companies. The study evaluated the effects of two air-spray chilling systems on the water absorption, cooling time, and the impact of both on the quality traits of the turkey meat.

Material and methods

Material

The experiment was carried out in a turkey slaughterhouse registered in the Federal Inspection Service, located in the Brazilian southern region.

120-carcass of male turkeys (Nicholas) aged between 145 and 160 days, and an average live weight of 18.5 kg were studied. The birds were grown on a turkey farm with 15 km away from the slaughter plant in a cooperative integrated system. The lairage time was 60 ± 10 min. Feed withdrawal took place 9:00 ± 0:30 h before slaughter, according to the standard industry practice.

The sequence of steps before the chilling were: hanging, electrically stunning (frequency 1000 Hz, current 250 mA, voltage 150 V), bleeding, scalding (55–58 °C for 180 s), defeathering and evisceration. Air-spray chilling processes were carried out immediately after the evisceration stage. All tests were performed in triplicate with 20 carcasses per test.

Experimental design

The quantitative and qualitative impacts of two air-spray chilling systems on turkey meat were evaluated. System A, currently used in this turkey slaughterhouse (control system) performed in two stages (air/water spray + air), and system B performed in a continuous process (air/water spray).

Air-spray chilling system A

The selected carcasses were weighed (TOLEDO 200316-2090) and identified. After measuring the temperature (TESTO 106), they were hung on individual hooks and carried on a continuous air conveyor for pre-cooling in the air and water spraying (ASC) chamber, with a capacity for 1540 carcasses, the temperature of − 0.5 °C, water spray 3.0 m3/h, water temperature 2 °C and air velocity 1.4 m/s. The carcasses remained in the chamber for 80 min. At the exit, the carcasses were weighed, manually transferred to rod hooks, and sent through rails to the air chamber (AC), with a temperature of − 2.5 °C and an airspeed of 1.4 m/s. The carcasses remained in the air chamber until they reached 4 °C in the depth of the pectoral musculature. Afterward, the carcasses were manually removed from the rods for the second weighing.

Air-spray chilling system B

The carcasses were weighed (TOLEDO 200316-2090) and identified. After measuring the temperature (TESTO 106), the carcasses were hung on individual hooks and sent on a continuous air conveyor to the air and water spraying (ASC) chamber, with a temperature of − 0.5 °C, water spraying of 3.0 m3/h, and airspeed of 1.4 m/s. The carcasses temperature was monitored every 80 min during the cooling period. Upon reaching 4 °C in the depth of the pectoral musculature, the carcasses were removed and weighed again.

Absorption percentage

The water absorption by the turkey carcasses was determined immediately after chilling according to Eq. (1) (European Commission 2012).

%ofabsorption=Finalweight-InitialweightInitialweight×100 1

Final weight—end of cooling (temperature of 4 °C).

Initial weight—before cooling.

Meat measurements

After determining the percentage of absorption in the carcasses, half a breast (left side) of each carcass was removed to perform the evaluations on turkey meat. Samples with an average weight of 2.1 kg were stored in plastic packaging, identified, frozen in a blast freezing tunnel at − 33 °C for 12 h with a product exit temperature of − 18 °C, and stored for about 10 days in a storage chamber (− 23 °C). The samples were thawed at refrigeration temperature (5 °C) for 24 h before the analyses.

Moisture protein ratio

Moisture content was measured by the gravimetric method, according to AOAC, (2000). Protein was determined by the Kjeldahl method, according to AOAC (2000). The Moisture:Protein Ratio (MPR) was obtained by dividing the percentage of moisture by the percentage of protein in the sample (AOAC 2000). All evaluations were performed in triplicates.

pH

The pH of the sample was determined according to the ISO 2917:1999 method (ISO 1999), using a portable digital meter (Mettler Toledo, FG2 FiveGo). All evaluations were performed in triplicates.

Color

Surface color (lightness (L*), redness (a*) and yellowness (b*) values) were measured with a colorimeter MiniScan XE Spectrophotometer (Hunter Associates Laboratory, Inc., Reston, Virginia, USA), with D65 illuminant and 10° viewing angle. Each value is the average result of three measurements (Zhuang et al. 2013).

Lipid peroxidation determination by TBARS

The thiobarbituric acid reactive substances (TBARS) assay was used for monitoring lipid peroxidation of the turkey meat using the method reported by Fernández et al. (1997). For this, 5.0 g of meat were homogenized in 15 ml of 0.38 M HClO4 for 3 min in an ice bath. It was added 0.5 ml of a 0.19 M ethanolic solution of butylated hydroxytoluene (BHT) to prevent further oxidation. The homogeneous solution was centrifuged (3.000 g, 5 min, 5 °C) and filtered on Whatman No 54 filter paper. After that, an aliquot of 0.7 mL was mixed with 0.7 mL of a TBA solution 0.02 M and heated in 100 °C C in a water bath for 30 min. After cooling, the mixture was centrifuged at 3.000 g for 15 min at 5 °C. Absorbance was measured at 532 nm on a spectrophotometer (Milton Roy, Rochester, NY). The results were expressed as mg malondialdehyde (MDA)/kg of sample. All evaluations were performed in triplicates.

Water retention capacity (WRC)

WRC analysis was performed using the procedure described by Wierbicki and Deatherage (1958). The sample of comminuted lean meat was wrapped in filter paper, placed between acrylic plates, and pressed immediately under the constant pressure of 500 p.s.i. for a minute. The press assembly was removed, and the first acrylic plate was separated. The plate containing the sample was directed against the light, and the areas formed by the meat film and the exudate were marked with a pen. The film was removed from the plate, and the marked areas were measured with image analysis software. The brown or red circular area (area of free water) of water absorbed by the paper filter was measured using image analysis software. All evaluations were performed in triplicates.

The calculation of the WRC is performed according to Eq. (2):

FreeH2O%=Aexudatecm2-Afilmcm2×9.47×100Totalsamplehumiditymg 2

Total sample humidity = sample weight × oven humidity.

9.47 means that each cm2 soaked contains 9.47 mg of water

WRC (%) = 100 − free H2O.

Shear force

The shear force analysis was performed according to Dadgar et al. (2010). Ten rectangular blocks of 1 cm2 cross-section allowing fiber direction parallel to a long dimension of 2–3 cm were cut from each cooked fillet. The shear force was determined using a TMS-Pro texture analyzer (model 2R1087, Food Technology Corp., Sterling, VA) equipped with a Warner–Bratzler shear blade. The sample was cut perpendicular to the direction of the fibers and the shear force, calculated as the average shear force from the ten samples.

Sarcomere length

Sarcomere length was assessed by the laser-diffraction method as described by Koolmees and Smulders, (1986). Parallel to the muscle fiber, small pieces (3.0 × 3.0 × 2.0 cm) were cut from different locations across the center of the pectoral muscle. The samples were fixed in glutaraldehyde solution. All evaluations were performed in triplicate.

Fatty acid profile

The composition of fatty acids was determined in fat extracted using the Soxhlet method (AOAC 2000). The extracted fat was esterified as described by Peisker (1964). The fatty acid methyl esters obtained (FAME) were analyzed by gas chromatography using a capillary gas chromatograph Agilent 68,650 Series GC System equipped with a DB-23 Agilent capillary column (60 m × 0.25 mm) according to the American Oil Chemists Society (AOCS 2009). Chromatograph operating conditions: carrier gas: He (1 mL/min); injector temperature: 250 °C; detector temperature: 280 °C; column temperature: 110 °C/5 min, 110–215 °C at 5 °C/min and then 215 °C/24 min. Fatty acids were identified based on their retention times. All evaluations were performed in duplicate.

Scanning electron microscopy (SEM)

Scanning Electron Microscopy was performed using the method described by Ribeiro et al. (2011). The samples were fixed (2.5% glutaraldehyde + 2% formaldehyde) in buffered solution (0.1 mol/L cacodylate) for 24 h, and afterward, they were washed in Cacodilate buffer solution (0.1 mol/L; pH 7.2–7.4). Subsequently, post-fixation in 1.0% Osmium Tetroxide solution was performed for one hour. The samples were dehydrated in an increasing gradient of ethanol (30, 50, 70, 90, and 100%) for 30 min each bath and dried at a critical point (Autosandri-815, Tousimis). Afterward, gold plating was performed in a metallizer (Desk V, Denton Vacuum). A scanning electron microscope (Tescan, mod. VEGA3—LMU) was used at 15 kV to view the samples.

Statistical analysis

The results were submitted to analysis of variance (ANOVA) followed by the Tukey test at a 95% confidence interval. The evaluations were performed with the aid of the XLSTAT software version 218.1.49386 for Excel.

Results and discussion

Evaluation of the air-spray chilling systems

In this study, in one of the systems evaluated (System A), the carcasses were pre-cooled in an air chamber and water spray (ASC) for 80 min, and the process was completed in the air chamber (AC), requiring more a time of 498 min for the carcasses to reach 4 °C at the depth of the pectoral musculature. At the end of the cooling stage, the turkey carcasses showed a weight reduction, concerning the initial weight (Table 1). According to Demirok et al. (2013), in the air chilling system, weight losses between 1 and 1.5% are common, in some cases, reaching 3%, depending on the capacity and type of system.

Table 1.

Weight difference, percentage of water absorption, and total cooling time of turkey carcasses refrigerated by two different air chilling systems

*Weight difference (grams) Water absorption (%) Total cooling time (minutes)
System A − 330a ± 24 − 1.78a 578b ± 17
System B  + 336b ± 31  + 1.82b 474a ± 3
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*Weight difference from the initial weight (before refrigeration)

System A - two stages (air/water spray + air)

System B - continuous process (air/water spray)

Means in the same column with different letters are significantly different (P < 0.05) by the Tukey test

In the chilling system B, the cooling occurred only in the air and water spraying (ASC) chamber, with a temperature of − 0.5 °C, water spraying of 3.0 m3/h. The carcasses remained in the chamber for 474 min to reach 4 °C in the depth of the pectoral musculature. Turkey carcasses had an average weight increase of approximately 1.82%. Table 1 shows the weight difference, percentage of water gain/loss, and total cooling time of turkey carcasses refrigerated by air chilling systems A and B.

When evaluating the results obtained in terms of weight gain or loss, the impact of the refrigeration process is evident. Air chilling system A promoted a significant (P < 0.05) weight reduction in the sample. In the second stage of this process (air chamber—AC), there was probably marked dehydration of the carcasses. Demirok et al. 2013, states that the cooled dry air can cause dehydration and alter qualitative aspects, such as discoloration on the surface.

In system B, on the contrary, there was a significant (P < 0.05) weight gain of the carcasses. Integral cooling with water spraying, reduced the loss of water by evaporation, where the appearance of the cooled carcass was similar to that of the carcasses cooled by immersion in water, mainly in the less thick limbs and with the greater contact surface, such as the neck, wings, thighs, and the walls of the thoracic cavity. The estimated difference between weight loss and gain was 0.66 kg/carcass. Considering the average value of US$ 0.80 kg/carcass of the turkey, this would represent a gain for the processing company of US$ 0.53 per turkey carcass.

It is important to emphasize that the use of chilling system B will imply the use of a greater amount of water in the process, which leads us to an assessment of the economic impacts. Considering that in system A, 3.99m3 of water was needed for pre-cooling (air chamber and water spraying—ASC) for 80 min of 1540 carcasses, it appears that 2.59 L of water/carcass were used. While in system B, to perform the complete cooling of 1540 carcasses, 23.7m3 of water was needed, that is, 15.38 L of water/carcass. Considering the average cost of US$0.06/m3 of water, the higher water consumption in system B (19.71 m3) would imply an increase in the cost of water of US$ 1.18 for the cooling of 1540 carcasses, while the gain in the US$ 0.53 per turkey carcass would represent an approximate profit of US$ 816.2 for the slaughterhouse.

However, the possible environmental implications of using more water in this continuous chilling process (system B) should also be considered. Further studies must be carried out in order to reduce the amount of water (3.0 m3/h) used. The optimization of the water spray and airspeed (1.4 m/s) parameters, possibly will allow the reduction of the volume or even the use of intermittent water sprays during the chilling process.

The processing time is a factor of great importance for the industries. More agile processes increase the company's efficiency, reducing production costs. The cooling time of carcasses in system B was significantly (P < 0.05) shorter than in system A (Table 1). The estimated time difference between the two systems, necessary for the turkey carcasses to reach 4 °C at the depth of the pectoral musculature, was 104 min, that is, an approximate 18% reduction in the cooling time. Considering the air and water spray chamber (ASC) capacity of 1540 carcasses, this reduction in cooling time would enable an increase in chilling capacity by an average of 278 turkey carcasses.

It should be considered that in addition to the shorter cooling time, the continuous system does not require the manual removal of carcasses from the line for allocation to the second chilling stage (system A), thus eliminating a cooling step (energy saving), being the fastest process, with greater biological safety for food and less demand for labor. According to Barbut (2014), with large-scale poultry slaughter operations, the companies demand fast and efficient processes, preferably without removing the carcasses from the line.

In addition, other possible advantages of continuous cooling (System B) should be considered, such as:

  • Greater control over production traceability;

  • Reduction of the risks of work accidents, due to rehanging carcasses on rod hooks for the second stage of cooling in the air chamber (AC);

  • Better control of the temperature of the carcasses.

Meat measurements

Pectoral muscle samples taken from refrigerated carcasses in systems A and B were used to evaluate meat quality. The moisture percentage and protein content of the samples refrigerated in system A were 74.5 ± 0.3% and 24.1 ± 0.6%, respectively. In system B, the samples had a moisture percentage of 75.2 ± 0.3% and protein content of 23.8 ± 0.3%.

The moisture: protein (MPR) ratio of the refrigerated samples in systems A and B were 3.09 and 3.14, respectively. The chilled turkey meat in both systems showed a similar MPR (P < 0.05). According to the European Union Implementing Regulation (EU) nº. 1239/2012 (European Commission 2012), the moisture: protein ratio (MPR) for skinless turkey breast cuts should be a maximum of 3.40 for air-cooled carcasses.

The percentage of moisture and protein are related to post-mortem conditions (Parteca et al. 2020). According to Pearce et al. (2011), the longitudinal and lateral contraction of the muscle fiber that occurs during post-mortem metabolism displaces water from the intra-myofibrillar space to the extra-myofibrillar space. Therefore, the greater the degree of post-mortem muscle changes, the greater the removal of water from inside the myofibrils. According to Zhuang et al. (2013), the water content of meat is strongly influenced by muscle pH.

The average pH value of the air chilled samples was 5.74 in system A, and 5.91 in system B. The refrigerated turkey meat in both systems did not present significant difference (P < 0.05) in the pH value. According to the United States Department of Agriculture (USDA 2019), the normal pH of turkey breast meat ranges from 5.7 to 6.1. The final pH of the muscle is one of the determining factors for meat quality and is related to glycogen depletion and release of lactic acid in the pre- and post-slaughter (Watanabe et al. 1996).

The formation of lactic acid and the consequent drop in pH post mortem can generate denaturation of muscle proteins and loss of solubility, reducing the water retention capacity (WRC) of meat (Hughes et al. 2014). The WRC of the sample refrigerated by system A was 56.2% ± 5.7% and system B, 62.3 ± 1.7%, both being below the value of 79.73%, described by Carvalho et al. (2014). The WRC of turkey meat refrigerated by system B was significantly (P < 0.05) higher than that refrigerated by system A. The lowest WRC of chilled meat in System A, possibly are related to its lower pH value. According to Goli et al. (2014) lower pH values result in meat with lower water retention capacity (WRC).

According to Carvalho et al. 2014, WRC has a direct correlation with the color of the meat. Excessive water loss is not desirable as it causes changes in color due to the loss of myoglobin along with water (Roque-Specht et al. 2009). Table 2 presents the results for shear force, sarcomere length, and color of turkey meat refrigerated by systems A and B.

Table 2.

Shear force, sarcomere length, and color of turkey meat (breast) refrigerated by two different air chilling systems

Air chilling systems Shear force (kgf) Sarcomere length (µm) L* a* b*
System A 3.94 ± 0.9a 1.88 ± 0.1a 71.76 ± 2.0b 2.25 ± 0.7b 16.54 ± 1.2b
System B 4.01 ± 1.2a 1.75 ± 0.0b 78.04 ± 2.6a 3.76 ± 0.8a 19.33 ± 1.5a
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System A - two stages (air/water spray + air)

System B - continuous process (air/water spray)

Means ± Standard Deviation. Means in the same column with different letters are significantly different (P < 0.05) by the Tukey test

According to Carvalho et al. (2014), turkey meat is considered clear when it presents L * values greater than 53. Dadgar et al. (2010), states that the luminosity values (L*) for turkey meat are between 46 and 53. In both air chilling systems, the luminosity values (L*) were higher than those described in the literature. The higher luminosity values (L*) may be related to aspects related to the birds evaluated in the study. It is known that the myoglobin content is the main determinant of color in the meat, this content being variable according to the species, muscle, and age of the animal (Çelen et al. 2016).

The L*, a*, and b* values of air-chilled turkey meat in system B were significantly (P < 0.05) higher than those from system A. The variation in meat color is possible due to the different percentages of water on the surface of the carcasses, refrigerated in each system. Refrigerated air is known to cause dehydration and discoloration of the carcass surface (James et al, 2006). The carcasses refrigerated in system A, suffered dehydration becoming opaquer, and therefore, with a lower luminosity value (L*). However, the results found for a* and b* were not expected due to the higher water absorption by the carcass in system B. It is known that dryness affects carcass light reflectance and background color increases redness and yellowness as a result of dehydration (Huezo et al. 2007).

It is known that scalding parameters can influence the color of poultry meat (Pool et al. 1954; Huezo et al. 2007; Jeong et al. 2011) According to Huezo et al., 2007, poultry carcasses that have undergone hard scalding, may experience a discoloration of the skin during air chilling. Higher temperature scalds, result in the loss of pigmentation of the skin due to removal of the cuticle or outer skin layer, exposing the surface that is very susceptible to dehydration and darkening on exposure to air (Pool et al. 1954). In this study, were used temperature and time parameters (55–58 °C for 180 s) considered intermediate, which made it possible to loosen the feathers without causing significant damage to the outer skin layers.

The postmortal sarcomere lengths have marked effects on textural properties of raw and cooked meat, and on water-holding especially in raw meat as well as indirect effects on color, taste, among others (Ertbjerg and Puolanne, 2017). The turkey breast meat refrigerated by system A had a higher (P < 0.05) sarcomere length than that refrigerated in system B. It is known that the length of the sarcomere is influenced by cooling and post-mortem metabolism (Aaslyng 2002). Possibly, the shorter length of the sarcomere of turkey meat refrigerated by system B, is related to the faster cooling of the carcasses, which reached lower temperatures in a significantly (P < 0.05) shorter time (Table 1). According to Aaslyng (2002), if the temperature of a muscle is below 10 °C before the onset of rigor mortis, shortening by cold can occur. Meat characteristics such as tenderness and WRC are directly related to the sarcomere length (Ertbjerg and Puolanne 2017).

The tenderness of turkey meat was assessed by determining the shear force (Table 2). Although turkey breast meat refrigerated in system B has a shorter sarcomere length, there was no significant difference (P < 0.05) in the shear force between samples cooled by systems A and B. According to Guo and Greaser (2017), meat tenderness is associated with many factors involving structural changes in muscle, protein breakdown, breakdown of high-energy compounds, enzyme activity, pH, temperature and processing time.

The evaluation of the lipid oxidation of turkey meat was performed using the TBARS method. The samples refrigerated in systems A and B presented similar lipid oxidation rates (P < 0.05), of 0.631 ± 0.02 and 0.634 ± 0.04 mg MDA/kg, respectively. These results were not expected due to the different hydration percentage of the refrigerated samples in each system. The chilled turkey carcasses in system A showed a reduction in weight due to the dehydration of the tissue, while the chilled carcasses in system B had an increase in weight due to water absorption. It was expected that the change in the percentage of water in the tissue would influence the oxidation index. It is known that lipid oxidation is strongly influenced by the water content, where dehydrated surfaces have a greater surface of contact with oxygen. Therefore, they are more susceptible to lipid oxidation.

It should also be noted that the turkey meat refrigerated by the two systems showed a high index of lipid oxidation when compared to the results described by Feng et al. (2017) (0.16 mg MDA/kg). Possibly, the high lipid oxidation is related to the high percentage of unsaturated fatty acids in the samples (Table 3). Both samples showed a high amount of unsaturated fatty acids when compared to the values described in other studies. Skiepko et al. (2014) and Mikulski et al. (2012) reported the percentage of unsaturated fatty acids in samples of chilled turkey breast of 63.15 and 65.27%, respectively.

Table 3.

Fatty acid profile (total fatty acid %) of turkey meat (breast) refrigerated by two different air chilling systems

Fatty acids System A System B
Lauric (C12:0) 0.24 ± 0.07 0.25 ± 0.14
Myristic (C14:0) 0.60 ± 0.04 0.49 ± 0.04
Pentadecanoic (C15:0) 0.14 ± 0.03 0.13 ± 0.02
Palmitic (16:0) 19.93 ± 1.95 19.46 ± 0.54
Margaric (C17:0) 0.26 ± 0.00 0.22 ± 0.04
Stearic (C18:0) 9.74 ± 0.53 9.84 ± 1.40
Arachidic (C20:0) 0.20 ± 0.01 0.19 ± 0.00
Behenic (C22:0) 0.15 ± 0.02 0.12 ± 0.00
Lignoceric (C24:0) 0.07 ± 0.03 0.09 ± 0.01
Palmitoleic (C16:1) 1.10 ± 0. 11 1.53 ± 0.92
Cis-10-heptadecenoic (C17:1) 0.08 ± 0.01 0.05 ± 0.00
Oleic (C18:1) 26.32 ± 0.10 24.92 ± 0.48
Linoleic (C18:2) 32.54 ± 2.65 32.74 ± 2.13
Trans elaidic (C18:1) 0.21 ± 0.23 0.13 ± 0.12
T-Linoleic (C18:2) 0.10 ± 0.00 0.34 ± 0.04
T-Linolenic (C18:3) 0.16 ± 0.04 0.10 ± 0.01
Linolenic (C18:3) 2.29 ± 0.04 2.24 ± 0.18
Conjugated linoleic acid (C18:3) 0.16 ± 0,02 0.13 ± 0.00
Eicosenoic (C20:1) 0.18 ± 0.00 0.19 ± 0.01
Arachidonic (C20:4) 4.42 ± 0.02 5.48 ± 1.27
Docosapentaenoic (C22:5) 0.62 ± 0.00 0.77 ± 0.24
Docosahexaenoic (C22:6) 0.44 ± 0.00 0.55 ± 0.21
% Saturated fatty acids* 31.35a 30.80a
% Unsaturated fatty acids* 68.65a 69.19a
MUFA 27.89a 26.82a
PUFA 40.73a 42.35a
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System A - two stages (air/water spray + air)

System B - continuous process (air/water spray)

*Means in the same line with different letters are significantly different (P < 0.05) by the Tukey test

MUFA Monounsaturated fatty acids, PUFA Polyunsaturated fatty acids

Turkey meat (breast) refrigerated by air chilling, presented a similar fatty acid profile (P < 0.05), independent of the chilling system (Table 3). The results showed that intramuscular fat from chilled turkey breast is an important source of polyunsaturated fatty acids (PUFA). The samples chilled in systems A and B, showed a high content of linoleic acid (C18: 2), with values around 32%. Among the monounsaturated fatty acids, oleic acid (C18: 1) and palmitoleic (C16: 1) showed the highest content. The content of saturated fatty acids was lower than those reported by Skiepko et al. (2014) for chilled turkey breast (36.85%). The saturated fatty acids palmitic (16: 0) and stearic (C18: 0) presented the highest content in both samples.

In our experiment, the turkey breast chilled in both systems showed a high content of unsaturated fatty acids, mainly polyunsaturated. Consequently, the levels of monounsaturated and saturated fatty acids were lower than those reported in other studies. It is known that the different percentages of fatty acids may be related to the feeding of birds. According to De Smet and Vossen (2016), in monogastric species, the composition of tissue fatty acids is a mirror of the composition of dietary fatty acids.

The morphological changes of the muscle, resulting from the air chilling process were evaluated by scanning electron microscopy (SEM). According to Pearce et al. (2011), different carcass chilling rates will affect the water dynamics in post mortem muscle by changing the water movements from the myofibrillar lattice to the extra-myofibrillar space.

In Fig. 1, it is possible to visualize the structure of the muscle submitted to air chilling in system A. In the 200 µm longitudinal sections (Fig. 1A), the presence of empty (dark) spaces between the myofibrils (marked area) is observed. These empty spaces are due to the marked loss of water during the cooling process. In Fig. 1B, with the 50 µm detail, it is possible to observe changes in the myofibrillar structure. The light points at the ends of the myofibrillar structure, with a more frayed appearance, indicate signs of dryness due to marked dehydration. These changes occurred due to the loss of intra and/or intermyofibrillar fluid during the chilling process.

Fig. 1.

Fig. 1

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Micrographs of turkey meat refrigerated in the air chilling system with two stages (air/water spray + air)

According to Honikel et al. 1985, the movement of water happens firstly from within the myofibrillar compartment into the inter-myofibrillar space and then into one of two other extra myofibrillar compartments, the inter and extra fascicular spaces.

On the other hand, it is observed that the muscle fibers of the turkey breast cooled in system B are more fragmented, as seen in the 200 µm longitudinal sections (Fig. 2A). In the 50 µm longitudinal sections (Fig. 2B) it is observed muscle fibers with protuberances and protrusions, due to the greater absorption of water in the tissue, which can be verified by the swelling of the fibers. The images presented in the scanning electron microscopy (SEM), confirm the results observed in the previous evaluations, where it was verified water absorption occurred in turkey carcasses air-chilled by system B, while in the refrigerated ones in system A there was water desorption.

Fig. 2.

Fig. 2

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Micrographs of turkey meat refrigerated in the air chilling system with a single stage (air/water spray)

Conclusion

The air chilling method influences the water absorption, cooling time, and some quality traits of turkey meat. Air chilling in a continuous process (air/water spray) decreases the cooling time by approximately 18%, and reduced the loss of water by evaporation, mainly in the less thick limbs and with the greater contact surface, resulting in an increase in the weight of the carcass. In this cooling process, the turkey meat showed a higher WRC and a shorter length of the sarcomere, however, no significant difference in the shear force was observed.

The air-spray chilling (control system) performed in two stages (air/water spray + air), was more prolonged and reduced the weight of the carcass. Turkey meat suffered dehydration becoming opaquer with a lower luminosity value (L*).

The air-spray chilling system in a continuous process is recommended to avoid economic losses, reduce the processing time and minimize the impacts of the chilling process in the meat quality traits.

Acknowledgements

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Author contributions

RFS conceived the idea, carried out the experiments and corrected the manuscript; NVP conceived the idea and corrected the manuscript; MMS carried out the experiments and corrected the manuscript; EBA wrote and corrected the manuscript; ATA conceived the idea, supervised the work, wrote and corrected the manuscript.

Funding

No funding was received to assist with the preparation of this manuscript.

Availability of data and material

The datasets generated during and/or analysed during the current study are available from the corresponding author on reasonable request.

Declarations

Conflict of interest

The authors have no conflicts of interest to declare that are relevant to the content of this article.

Footnotes

Publisher's Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

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Associated Data

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Data Availability Statement

The datasets generated during and/or analysed during the current study are available from the corresponding author on reasonable request.

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