Alterations in the Water Properties of Wooden Breast Fillets During the First 24 h Postmortem

Introduction

Intensive genetic selection and optimized nutritional programs have enhanced efficiency and production in modern broiler farming (Goo et al., 2025). However, muscle myopathies, such as wooden breast (WB) syndrome, have become increasingly common in fast-growing broilers (Che et al., 2022). The WB syndrome is characterized by abnormal muscle hardness and diminished meat quality, which decreases consumer acceptance and causes tremendous economic losses to the poultry industry (Pedrão et al., 2021). High moisture content and reduced water-holding capacity are typical characteristics of WB fillets, potentially impacting meat yield, quality, shelf life, and consumer acceptance (de Almeida Assunção et al., 2020; Li et al., 2024).

The physical and chemical changes in chicken muscle after slaughter are crucial in shaping the final meat quality. Gaining deeper insights into the critical early postmortem phase of muscle-to-meat conversion will enhance our understanding of the factors influencing broiler meat quality. In chickens, rigor mortis development typically starts within the first hour postmortem and is completed by 4 h to 6 h (Papa and Fletcher, 1988; Sams and Janky, 1991). Rigor mortis can impact water-holding capacity by inducing a shrinkage in muscle fiber diameter and increasing the extracellular space around the fibers, which can decrease the amount of immobilized water and increase the amount of free water (Huff-Lonergan and Lonergan, 2005). Time-domain nuclear magnetic resonance (NMR) is a fast, nondestructive technique for evaluating the mobility and distribution of different water populations within muscle. It has proven valuable in exploring the relationships between water properties (water mobility and distribution) and water-holding capacity in meat (Bertram et al., 2002a; Pang et al., 2021; Zhang et al., 2022). However, limited data are available to understand water property dynamics in chicken meat during the early postmortem phase when many important biophysical changes occur in the muscle that may impact final meat quality. Therefore, this study aimed to examine changes in water properties of normal (N) and WB chicken breast fillets during the first 24 h postmortem as muscle transitions to meat.

Materials and Methods

Sample collection, purge loss, pH, and temperature

In each of 3 independent trial replicates, sixty 56-d old Cobb 500 male broiler chickens were used, with an equal number of birds preselected for N and WB conditions using breast muscle palpation. Birds were transported for approximately 5 to 10 min from the University of Georgia Poultry Farm (Athens, GA) to the US National Poultry Research Center pilot processing plant (Athens, GA). Slaughter was conducted in accordance with an approved animal use proposal (Protocol Number: USNPRC-2024-07) (Choi et al., 2022). Immediately following electrical stunning and bleeding out, breast muscles were exposed and assessed for the presence and severity of the WB condition by trained experts. In each replicate, 5 N (no WB) and 5 severe WB carcasses were selected for further analysis. The breast muscles (Pectoralis major) of selected carcasses were immediately deboned (5–10 min postmortem). Deboned fillets were reassessed WB scores on a 3-point scale with 0.5 point increments (1 = no WB, 2 = moderate WB, 3 = severe WB) (Pang et al., 2020b). The average scores of the N group and WB group were 1.1 and 2.6, respectively in 3 replicates.

From each carcass, 1 fillet was used for water property, pH, and purge loss measurements, and the other fillet was used for texture, proximate composition, and color measurements. Using a cutting frame, the fillets designated for water property measurements were trimmed to equal dimensions (10 × 10 × 2 cm) from the cranial-ventral portions of the fillets to reduce potential temperature variation during fillet chilling. All samples (trimmed fillet portions and intact fillets) were placed in individual sealed plastic bags and chilled on ice for 7 h before being moved to a 4°C refrigerator. Fillet portions were weighed at 0 h (5–10 min), 0.5 h, 1 h, 2 h, 3 h, 4 h, 5 h, 7 h, 9 h, 12 h, 24 h, and 48 h postmortem after being removed from the bag and gently blotted dry to determine purge loss. Noncumulative purge loss per hour was calculated based on weight changes between consecutive time points, while cumulative purge loss was determined as the total weight loss over the entire measurement period. Cumulative purge loss was calculated using the difference between the initial fillet weight (at 0 h postmortem; W_Init) and the post-storage weight (W_Post) at each sampling time point, using the following formula:

$\mathrm{cumulative}\mathrm{purge}\mathrm{loss}(\%)=100\times [({\mathrm{W}}_{\mathrm{Init}}–{\mathrm{W}}_{\mathrm{Post}})/{\mathrm{W}}_{\mathrm{Init}})]$

At each time point, the pH of fillet portions was measured at the cranial end of the samples using a Thermo Scientific Orion Star A220 pH meter (Thermo Scientific, Pittsburgh, PA), equipped with a spear-tip probe (Thermo Scientific Orion 8163BNWP, Thermo Scientific) (Choi et al., 2022). The pH meter was calibrated using pH 4.0 and pH 7.0 standard buffers before each time point, and the probe was rinsed with deionized water between measurements. Sample temperatures were recorded using a temperature data logger equipped with thermocouple needles (Model SD-947, Reed Instruments, Wilmington, NC). The average temperature profiles of the samples are presented in Figure 1.

Figure 1.

Temperature of normal and wooden breast fillet portions during the first 7 h postmortem. Two-way analysis of variance with repeated measurements was used to analyze the effects of postmortem time (Time), WB condition (WB), and their interactions (WB × Time). The significance level was set at .05 (P < .05). Symbol with error bars = mean ± SE, n = 15. N, normal; WB, wooden breast.

Measurement of transverse relaxation time using time-domain nuclear magnetic resonance

At 0 h, 0.5 h, 1 h, 2 h, 3 h, 5 h, 7 h, 12 h, and 24 h postmortem, transverse relaxation time (T2) was measured in fillet portions using a time-domain ¹H NMR analyzer (Bruker LF90II Proton-NMR, Bruker Biospin GmbH, Rheinstetten, Germany) after samples were blotted dry. The analyzer was equipped with a sample holder (89 mm outer diameter) and operated at a magnetic field strength of 0.12 T, corresponding to a resonance frequency of 6.2 MHz for protons, as described by Pang et al. (2023). Carr-Purcell-Meiboom-Gill sequences were used to measure T2 relaxation with the following parameters: a 90° to 180° pulse separation (tau) of 2 ms, a total of 500 acquired echoes, and 16 scan repetitions. The distribution of T2 relaxation decays was analyzed using the CONTIN regularization algorithm (Provencher, 1982) provided by Minispec (Bruker Biospin GmbH, Rheinstetten, Germany). The analysis identified 4 distinct water populations in the breast fillets based on their T2. T2b (4–5 ms) represents water strongly bound to macromolecules or hydration water, while T21 (40–60 ms) corresponds to intramyofibrillar (immobilized) water. T22a (80–210 ms) represents a portion of the extramyofibrillar water or free water with lower mobility, whereas T22b (210–500 ms) represents a portion of the extramyofibrillar water or free water with higher mobility (Figure 2). The proportions of these water components, expressed as a percentage of the total peak areas, were designated as P2b, P21, P22a, and P22b, respectively. Additionally, the normalized abundance of each water component (per 100 g of meat) was denoted as A2b/100 g, A21/100 g, A22a/100 g, and A22b/100 g.

Figure 2.

Distribution of transverse relaxation time (T2) and the corresponding water populations in broiler breast meat includes: T2b (4–5 ms) representing strongly bound water associated with macromolecules or hydration water, T21 (40–60 ms) representing immobilized water located within the intramyofibrillar compartment, T22a (80–210 ms) representing free water with lower mobility within the extramyofibrillar compartment, and T22b (210–500 ms) representing free water with higher mobility in the extramyofibrillar compartment. The X-axis (relaxation time in ms) is presented on a logarithmic scale (base 10) to better visualize the distribution of these water components. Reprinted from Choi et al., 2024.

Statistical analysis

GraphPad Prism (Version 9.1.0; GraphPad Software, San Diego, CA) was used for statistical analyses and graph construction. The effects of WB condition, postmortem time, and their interactions were evaluated using 2-way analysis of variance with repeated measures. Segmented linear regression was applied to determine slopes and inflection time points (Figure 3). If an inflection time point could not be calculated, it was reported as nonapplicable. For compression force, proximate composition, and color measurements, mean comparisons were performed using an unpaired t-test. Statistical significance was set at P < .05. For this experiment, the bird served as the experimental unit, and the sample size was n = 15.

Figure 3.

Illustration of slopes (slope 1 and slope 2) and the inflection time point (X0) in segmented linear regression analysis.

Results

Water properties (T2 relaxation)

T2 relaxation distributions, including relaxation times (T2b, T21, T22a, and T22b), relative proportions (P2b, P21, P22a, and P22b), and abundance per 100 g of meat (A2b, A21, A22a, and A22b) for both N and WB fillets during the first 24 h postmortem are presented in Figure 4. Significant interactions between postmortem time and WB condition were observed for T2b, T21, T22a, and T22b (P < .05). Whereas relaxation patterns varied with meat condition and postmortem time, T2b, T21, and T22a were significantly influenced by postmortem time (P < .05) in all samples with WB fillets consistently exhibiting greater T2b, T21, and T22a values compared to N fillets. For T22b, there was also a significant interaction between postmortem time and WB condition (P < .05). WB fillets had consistently greater T22b values than N fillets. However, T22b was not significantly affected by postmortem time (P > .05).

Figure 4.

The changes in water properties of normal and wooden breast fillets during the first 24 h postmortem were measured, including T2b (4–5 ms) representing water strongly bound to macromolecules or hydration water, T21 (40–60 ms) representing immobilized water in the intramyofibrillar compartment, T22a (80–210 ms) representing free water with lower mobility in the extramyofibrillar compartment, and T22b (210–500 ms) representing free water with higher mobility in the extramyofibrillar compartment. The corresponding proportions (P2b, P21, P22a, P22b) and abundance (area/100 g of meat) (A2b/100 g, A21/100 g, A22a/100 g, A22b/100 g) of these water populations were also assessed. The effects of postmortem time (Time), WB condition (WB), and their interactions (WB × Time) were analyzed using 2-way analysis of variance with repeated measurements. The significance level was set at P < .05. Segmented linear regression analysis was employed to determine the inflection time points. If the inflection time point was not calculable, it is indicated as not applicable. Symbol with error bars represents mean ± SE, with n = 15. N, normal; N/A, not applicable; WB, wooden breast.

There were no significant interactions between postmortem time and WB condition for the relative proportion of each water population (P2b, P21, P22a, and P22b). However, postmortem time had a significant effect on P2b, P21, and P22b (P < .05) but not on P22a. WB fillets consistently exhibited lower P2b and P21 but greater P22b compared to N fillets. While P22a was consistently greater in WB fillets, it was not significantly influenced by postmortem time (P > .05).

While no interaction effects were observed for A2b, A22a, and A22b (P > .05), A21 was significantly affected by the interaction between postmortem time and WB condition (P < .05). Postmortem time influenced A2b, A21, and A22b (P < .05) but had no significant effect on A22a (P > .05). WB fillets consistently exhibited greater A21, A22a, and A22b compared to N fillets, while A2b showed no significant difference between N and WB fillets.

Slopes and inflection time points of T21, P21, A21, P22b, and A22b

The comparison of the slopes and inflection time points of T21, P21, A21, P22b, and A22b between N and WB fillets are shown in Figure 5. Regardless of the T2 parameters and WB condition, the absolute values of slope 1 (the first slope before the inflection time point) were consistently greater than the absolute value of slope 2. After the inflection time point, the values of slope 2 approached 0, suggesting a plateau was reached. The inflection time points were constructed approximately between 2 h and 5 h. For T21, P21, P22b, and A22b, the WB fillets had consistently earlier inflection time points compared to the N fillets. As shown in Figure 5, the slopes of P21 for N and WB were in opposite directions to those of the P22b slopes for N and WB. However, the absolute values of inflection time points of P21 were similar to those of P22b: they were 3.802 h for N and 3.277 h for WB for P21 and 3.777 h and 3.054 h for P22b, respectively. However, no such relationships were noted between P21 and P22a and between P22a and P22b regardless of WB condition.

Figure 5

Comparisons of slopes and inflection time points of normal and wooden breast fillets in T21 (relaxation time for intramyofibrillar water), P21 (proportion of intramyofibrillar water), A21 (abundance/100 g of meat of intramyofibrillar water), P22b (proportion of extramyofibrillar water), and A22b (abundance/100 g of meat of extramyofibrillar water). Inflection time points were calculated by using segmented linear regression. N, normal; WB, wooden breast.

Average differences in water properties between normal and wooden breast fillets

The average differences in water property parameters between N and WB fillets are shown in Figure 6. Differences in relaxation time (T2b, T21, T22a, and T22b) peaked at 3 h postmortem. However, noticeable trends in postmortem times of peak differences were not observed in the relative proportions (P2b, P21, P22a, and P22b) or abundances (A2b, A21, A22a, and A22b) of the 4 water populations.

Figure 6.

The average differences in water properties between normal and wooden breast fillets were analyzed based on T2 relaxation time constants and their corresponding proportions and abundance. The measured time constants included T2b (4–5 ms) representing water strongly bound to macromolecules or hydration water, T21 (40–60 ms) representing immobilized water in the intramyofibrillar compartment, T22a (80–210 ms) representing free water with lower mobility in the extramyofibrillar compartment, and T22b (210–500 ms) representing free water with higher mobility in the extramyofibrillar compartment. The relative proportions (P2b, P21, P22a, P22b) and abundance per 100 g of meat (A2b/100 g, A21/100 g, A22a/100 g, A22b/100 g) were compared between N and WB fillets to evaluate how the WB condition affects water distribution and mobility in broiler breast meat. N, normal; WB, wooden breast.

pH and purge loss

The pH decline patterns of N and WB fillets during the first 24 h postmortem are shown in Figure 7. There was a significant interaction between postmortem time and WB condition on breast meat pH (P < .05). The inflection time point of pH decline in WB fillets (6.263 h) occurred earlier than in N fillets (8.295 h). Additionally, the absolute value of slope 1 in WB fillets was greater than that of N fillets (N: −0.132 vs. WB: −0.147), indicating a more rapid initial decline in pH for WB fillets.

Figure 7.

The pH of normal and wooden breast fillets during 24 h postmortem. Two-way analysis of variance with repeated measurements was used to analyze the effects of postmortem time (Time), WB condition (WB), and their interactions (WB × Time). The significance level was set at .05 (P < .05). Segmented linear regression analysis was conducted to calculate the slopes and inflection time points. Symbol with error bars = mean ± SE, n = 15. N, normal; WB, wooden breast.

The noncumulative and cumulative purge loss of N and WB fillets during the first 24 h postmortem are presented in Figure 8. Significant interactions were observed between postmortem time and WB condition for both noncumulative purge loss per hour and cumulative purge loss (P < .05). Noncumulative purge loss fluctuated over the 24 h postmortem period in both fillet types (P < .05), with WB fillets consistently exhibiting greater purge loss per hour compared to N fillets. Similarly, cumulative purge loss increased over time in both fillet types (P < .05), with WB fillets showing significantly greater overall purge loss than N fillets (P < .05).

Figure 8.

Noncumulative and cumulative purge loss of normal and wooden breast fillets during 24 h postmortem. Noncumulative purge loss was calculated as purge loss per hour. Two-way analysis of variance with repeated measurements was used to analyze the effects of postmortem time (Time), WB condition (WB), and their interactions (WB × Time). The significance level was set at .05 (P < .05). Segmented linear regression analysis was conducted to calculate the inflection time points. Symbol with error bars = mean ± SE, n = 15. N, normal; WB, wooden breast.

Discussion

In a previous study (Choi et al., 2024b), changes in water properties of N and WB chicken breast fillets collected after immersion chilling (∼4 h postmortem) through 7 d of refrigerated postmortem storage were reported. The current study focused specifically on the water properties of broiler breast muscle from slaughter through the first 24 h postmortem, when many critical physical and chemical changes occur in the muscle tissue such as pH and temperature decline and rigor mortis development. A previous study by Tasoniero et al. (2020) showed that early postmortem changes in breast muscles are different between N and WB fillets. It is of interest to investigate further the effect of the WB myopathy on changes in muscle water properties during rigor mortis development, which was not feasible in previous work (Choi et al., 2024b). Another difference between the present study and the previous one is deboning time. In the current study, broiler breast fillets were deboned immediately after bleeding instead of 3 h postmortem as in the previous study.

Chilling is a critical step to maximize meat quality and secure food safety in poultry processing (Demirok et al., 2013). In the current study, immediately following broiler stunning and bleeding, breast fillets were deboned and placed on ice to simulate chilling conditions. Samples were chilled in sealed plastic bags to prevent the breast muscle from picking up water during chilling which could impact water properties within the tissue. The temperature of fillets dropped below 4°C in 120 min (Figure 1), exhibiting similar trends to immersion water chilling, as observed in a previous study by Lee et al. (2020). This approach allowed the investigation of early postmortem water property dynamics in breast meat without the confounding factor of water uptake during chilling. Elucidating the effects of immersion water chilling on muscle water properties of breast fillets on intact broiler carcasses would require additional research and was outside the scope of this study. The relatively greater absolute values of purge loss observed in this study compared to literature values (1–3% at 24–48 h) (Kaić et al., 2023) can be attributed to the hot deboning procedure, increased cut surfaces of fillet portions, and repeated blot drying of samples prior to each NMR measurement, which likely enhanced the removal of loosely bound surface water.

In the current study, the postmortem time and the WB condition significantly affected relaxation times of 3 of the 4 water populations (T2b, T21 and T22a), and there were interactions between postmortem time and WB condition. These data are consistent with previously published results in broiler fillets (Tasoniero et al., 2017; Pang et al., 2020a; Choi et al., 2024b). Greater relaxation times indicate that hydrogen protons take a longer time to return to their original state, which could be indicative of weakened interactions between water and macromolecules (T2b), less space limitations within the myofibrillar structures (T21), or changes in extramyofibrillar compartment space and a reduced ratio between water and areas of macromolecule interface in extramyofibrillar compartments (T22a and T22b). Such changes could lead to a redistribution among the different muscle water populations (Li et al., 2012). In a study that investigated the effects of water addition, sodium chloride, and pH on T2 relaxation rate in minced hake, Duflot et al. (2019) demonstrated that T2 relaxation time increased with increasing protein concentration or by addition of water to muscle. Bertram et al. (2002b) reported a strong and positive correlation between the T21 time constant and sarcomere length in pork muscle tissue and ascribed the changes in T21 to the structural features associated with changes in sarcomere length. Wu et al. (2006) investigated the influence of aging and salting on water distribution in pork and concluded that the decrease in T2 time constant generally reflects the loss of water and shrinkage of myofibrils, while the increase of T2 indicates the gain of water content as well as the swelling of meat proteins. The findings in the current study further demonstrate that the WB condition may alter both muscle structural features and the ratio of water to macromolecular surfaces.

It is worth noting that comparisons of differences in T2 measurements between N and WB fillets showed consistent trends in T2b, T21, T22a, and T22b throughout 24 h postmortem, with differences peaking at 3 h postmortem. These results suggest that the effect of the WB condition on water properties in broiler breast meat might be linked to the full development of rigor mortis, which typically occurs around 2 h to 4 h postmortem in broiler breast meat (Sams, 1999; Li et al., 2010). These results also suggest that rigor mortis may differentially influence water-macromolecule interfaces for T2b and both compartmental space and water-macromolecule ratios of intramyofibrillar and extramyofibrillar water populations in WB fillets compared to N fillets (Bertram et al., 2002b; Wu et al., 2006; Duflot et al., 2019).

The data also revealed that the inflection time points of P21, P22b, A21, and A22b occurred between 2 h to 4 h postmortem. Additionally, the absolute value of the first slope (before the inflection time point) was greater than that of the second slope (after the inflection time point), suggesting a more rapid change in water properties during the early postmortem phase. Moreover, the second slope after the inflection time point was approximately 0. These indicate that regardless of meat condition, the most dramatic changes in the intramyofibrillar water and extramyofibrillar water populations occurred during the early phase of rigor mortis, and, afterward, there were only minor changes in the water populations of the tissue. Bertram et al. (2004) showed that intramyofibrillar water increased in the early postmortem period and then subsequentially decreased, while extramyofibrillar water decreased early postmortem and then increased in porcine M. longissimus. This led to the hypothesis that increased intramyofibrillar water in prerigor muscle (e.g., early postmortem) may be due to cellular swelling as myofibers absorb water by increasing intracellular osmolarity. Afterward, the longitudinal shrinkage and disruption of membrane structure due to rigor mortis expel the intramyofibrillar water into the extracellular space in the muscle. Chicken breast fillets undergo similar rigor mortis related ultrastructural changes to porcine muscle; however, compared with pork, the timing of these events may be accelerated. In chicken muscle, rigor onset is early (<1 h postmortem), and full rigor mortis development and myofibrillar shrinkage are rapid (3–6 h postmortem) compared to other species (Sams, 1999; Li et al., 2010). According to Bertram et al. (2004), the proportion of intramyofibrillar water (P21) would be expected to decrease during rigor mortis at 2 h to 4 h postmortem in chicken breast fillets. However, in the current study, both the relative proportion (P21) and normalized abundance (A21) of the intramyofibrillar water population increased with increased relaxation time (T21) from 5 h to 7 h postmortem and remained relatively steady until 24 h postmortem. Increased intramyofibrillar water has been ascribed to increases in intramyofibrillar space in meat (Ge et al., 2021). The data of T21, P21, and A21 from the current study all suggest that rigor mortis potentially provided more space for intramyofibrillar water in the chicken breast meat perhaps due to myofiber swelling instead of reducing space during postmortem period, as hypothesized in pork meat by Bertram et al. (2004). Further studies are warranted to understand the relationships among changes in T21, sarcomere length, and myofiber swelling in chicken breast meat during rigor mortis.

Analysis of the inflection time points and slopes of water property measurements over 24 h postmortem further showed that the patterns matched well for the proportion of intramyofibrillar (P21) and extramyofibrillar water with greater mobility (P22b) in both N and WB fillets (Figure 5). Bertram et al. (2004) demonstrated that intramyofibrillar and extramyofibrillar water can be interchangeable during rigor mortis and hypothesized that there is a dynamic shift of immobilized water (T21) to free water (T22), or water moves from the intramyofibrillar compartment to the extramyofibrillar compartment during rigor mortis and meat aging. The water with higher relaxation time might move into the intramyofibrillar water in broiler fillets during rigor mortis. Similarly, the matched inflection time points and slopes in the current study also suggest water movement between the intra- and extramyofibrillar compartments with a direction opposite to what Bertram et al. (2002a; 2004) observed in red meats. These differences may be attributed to variations in muscle fiber composition, the rate of sarcoplasmic and myofibrillar protein denaturation, and the chilling process. In broiler fillets, the rapid postmortem metabolic changes and structural disruptions likely cause water with higher relaxation times to migrate into the intramyofibrillar compartments during rigor mortis, highlighting a fundamental distinction between white and red meat muscle postmortem.

The noncumulative purge loss per hour showed similar postmortem trends to P22b. These results suggest that the extramyofibrillar water with higher relaxation time (T22b) may also be responsible for water loss in chicken breast meat. Since distribution analysis of T2 relaxation classifies water or hydrogen protons based on mobility, water molecules existing next to myofibrils or outside of the muscle fiber could both be designated as T22b. Thus, it is feasible that highly mobile water molecules could be involved in both water exchange between intra- and extramyofibrillar compartments and drip loss. These data support previous findings that extramyofibrillar water with higher relaxation time can either move into the intramyofibrillar water compartment or move outside of the meat as drip (Pearce et al., 2011; Choi et al., 2024b).

In the current study, the inflection time points for T21, P21, P22b, and A22b in WB fillets were lower than those of N fillets throughout 24 h postmortem. This indicates that water movement during rigor mortis plateaus earlier in WB fillets compared to N fillets. This may be associated with the compromised energy metabolism with lower level of glycogen, glucose, adenosine triphosphate (ATP), and lactic acid production, which are essential for rigor mortis development, in WB fillets compared to the N fillets (Baldi et al., 2020; Zhang et al., 2020; Choi et al., 2024a). Muscle pH is a good indicator for the level of lactic acid and ATP production during rigor mortis. In the current study, a lower inflection time point of pH in WB fillets than in N fillets was observed, which also suggests that rigor mortis completed earlier in WB fillets compared to N fillets. This was further supported by the greater absolute values of the slope before the inflection time points (slope 1) in T21, P21, P22b, A22b, and pH of WB fillets compared to the N fillets. The greater noncumulative purge per hour observed in WB fillets in the early postmortem phase was likely due to a greater abundance of free water (A22a and A22b) and greater overall water content in the WB fillets compared to N fillets. After death, a high calcium level in the sarcoplasm of the muscle cell is the initiator of the process of myosin and actin molecules interacting to form cross-bridges as in muscle contraction (Smith et al., 2013). As ATP is depleted, the myosin and actin form permanent cross-bridges (i.e., rigor mortis). Previous work has shown that WB fillets have greater calcium content than N fillets (Welter et al., 2022). Potentially, the greater calcium concentrations may accelerate rigor mortis development, but the lack of ATP may induce the early completion of rigor mortis in WB fillets compared to N fillets. Relating how postmortem biochemical changes impact mechanical strength in WB, Hasegawa et al. (2020) suggested that WB fillets retain postmortem hardness and stiffness due to a greater abundance of connective tissue that is unaltered during the postmortem period, suggesting that WB fillets may experience physical limitations during rigor mortis progression (Soglia et al., 2018; Zhang et al., 2020; Kaewkot et al., 2024). Differences in inflection time points between N and WB fillets may not be observed if fillets are deboned at the typical postchill stage (∼3 h postmortem) as the breast muscle is fixed to the keel bone, and therefore sarcomere contraction is inhibited during the initial stages of rigor mortis development (Puolanne et al., 2021). Therefore, it would be of interest to investigate the effects of deboning time on sarcomere contraction as well as water movement in N and WB fillets. In addition to sarcomere shortening during rigor mortis and connective tissue, postmortem muscle protein degradation normally influences meat texture and quality characteristics. Although Kaewkot et al. (2024) observed a reduced myofibril fragmentation index in severe WB meat compared to N meat, others have reported increased postmortem protein degradation in WB meat (Soglia et al., 2018; Zhang et al., 2020) but concluded that the increased hardness of WB was not likely due to differences in the proteolytic process. Likewise, in the current study, any potential differences in postmortem proteolysis between N and WB meat were not thought to have a substantial impact on quality differences as measurements were taken at 24 h postmortem.

In conclusion, water properties (water population/distribution, mobility, and abundance) in chicken breast fillets undergo dynamic changes during the early postmortem phase (3–5 h) and then subsequently reach a plateau. The extramyofibrillar water with greater relaxation time (or greater mobility) disappears rapidly in broiler breast muscle in the first 24 h postmortem, either moving into the intramyofibrillar compartment and/or moving outside of fillets as water loss. Chicken breast meat with the WB condition has a larger proportion of muscle water with greater mobility than N breast meat, and the WB myopathy significantly impacts the water properties of the meat during the critical early postmortem phase. Data from this study suggest that the dynamic postmortem changes in muscle water properties occur earlier postmortem in WB meat compared to N meat. Differences in rigor mortis development early postmortem may result in differences in water properties and water movements in WB fillets. This study provides useful data for understanding muscle water movement/redistribution in N and WB chicken breast fillets during the early postmortem phase and the mechanisms that control water-holding capacity in chicken breast meat.

Conflict of Interest

The authors declare no conflict of interest. The use of trade, firm, or corporation names in this publication is for the information and convenience of the reader. Such use does not constitute an official endorsement or approval by the US Department of Agriculture or the Agricultural Research Service of any product or service to the exclusion of others that may be suitable.

Author Contribution

Janghan Choi: conceptualization, methodology, experimental design, data curation, formal analysis, visualization, experiment execution, and writing—original draft, review, and editing; Majid Shakeri: methodology, experiment execution, and writing—review and editing; Caitlin Harris: methodology, experiment execution, and writing—review and editing; Jeff Buhr: methodology, experiment execution, and writing—review and editing; Woo Kyun Kim: methodology, experiment execution, and writing—review and editing; Byungwhi Kong: methodology, experiment execution, and writing—review and editing; Brian Bowker: methodology, experiment execution, writing—review and editing, and supervision; and Hong Zhuang: conceptualization, experiment execution, methodology, project administration, resource acquisition, supervision, validation, and writing—review and editing.