Effect of NaCl Concentration and Cooking Temperature on the Color and Pigment Characteristics of Presalted Ground Chicken Breasts

The processing was performed with slightly modified procedure from a previous study (Claus and Jeong, 2018). Fresh, skinless, boneless chicken breasts (1 d postmortem) were obtained from a local processor (Kwangsung Food, Korea). Raw material was shipped in an insulated cooler and refrigerated (2–3°C) until use. Three separate replicates of ground chicken breast were used in this study. From each replication, a representative sample of raw ground chicken was used for pH determination and residual nitrite content analysis. A total of 20 kg of raw chicken trimmings was used for each replication and ground with a 0.3 cm plate using a chopper (TC-22 elegant plus, Tre Spade, Italy). The ground meat was randomly divided into four batches (4 kg each), based on NaCl concentrations (0%, 1%, 2%, and 3% NaCl). Each batch of ground meat was mixed with 0%, 1%, 2%, or 3% NaCl using a mixer (5K5SS, Whirlpool Inc., USA) for 10 min and individually vacuum-packaged with a vacuum packaging machine (M6-TM, Leepack Co., Ltd., Korea) in polyethylene/nylon bags, which were then stored for 7 d under refrigeration (2–3°C). After 7 d, each batch was remixed (5K5SS, Whirlpool Inc., USA) for 5 min, and air pockets were removed in a vacuum chamber (M6-TM, Leepack Co., Ltd., Korea); the batched were then stuffed into conical centrifuge tubes (approximately 50 g each). The tubes were centrifuged at 2,000×g for 10 min (FELTA5, Hanil Science Corp., Korea) to remove air pockets. All the samples were then cooked to four different endpoint temperatures (70°C, 75°C, 80°C, and 85°C, respectively) in a 90°C water bath (CB60L, Dongwon Scientific Machinery Corp., Korea) and the temperature was monitored by randomly placing four thermocouples attached to a 4-channel digital thermometer (Tes-1384, Ketech Scientific Instrument Co., Ltd., Taiwan) in the center of the extra samples in the water bath. After cooking, the samples were immediately cooled on ice for 20 min and stored at 2–3°C overnight in the dark, until further analysis. The experiments were replicated thrice.

Stuffed ground chicken meat samples were weighed prior to cooking to determine the raw sample weight. Cooked weights were measured prior to color measurements to determine yield. Cooking yield was calculated as: [cooked sample weight/raw sample weight]×100. A pH meter (Accumet AB50, Thermo Fisher Scientific Inc., Singapore, Singapore) was used to measure the pH of 5 g of raw meat or cooked chicken samples homogenized in 25 mL of distilled, deionized water. ORP of cooked turkey products was measured, following the modification of Cornforth et al. (1986) and John et al. (2005). A sample (10 g) from each chicken product was homogenized (DI 25 basic, IKA-Werke Gmbh & Co. KG, Germany) with 20 mL of 0.1 M sodium carbonate for 15 s at 13,000 rpm. Fifty microliters of butylated hydroxytoluene (BHT, 7.2% in ethanol) was added to minimize sample oxidation during blending. The ORP values were determined after 3 min of stabilization using a platinum Ag/AgCl combination electrode (Model 13-620-631, Thermo Fisher Scientific Inc., Singapore) attached to the pH meter set to the milli-volt scale.

CIE (L*, a*, b*) values were measured on freshly cut surfaces of cooked samples using a chroma meter (CR-400, 8 mm aperture, illuminant C; Konica Minolta Corp., Japan) calibrated with a white plate (L* 94.90, a* –0.39, b* 3.88). CIE (Commission Internationale de l'Eclairage) measurements were used to determine lightness (CIE L*), redness (CIE a*), and yellowness (CIE b*). Two slices were cut parallel to the longitudinal axis of each ground chicken breast sample, and 3 measurements per slice (six readings per sample) were taken immediately after cutting.

Myoglobin (Mb) was extracted from uncooked or cooked turkey breast products using the method published by Warriss (1979) and Trout (1989). The extracted supernatants were clarified by filtration through Whatman No. 1 filter paper, and absorbance was determined at 525, 572, and 700 nm (Krzywicki, 1979) using a UV/VIS spectrophotometer (UV-1800, Shimadzu Corp., Kyoto, Japan). The total myoglobin (Mb) and PMD were calculated using the following formulas (Trout, 1989): Mb (mg/g)=(A₅₂₅–A₇₀₀)×2.303×dilution factor, PMD=[1–(Mb concentration after heating/Mb concentration before heating)]×100. To obtain the percentage reflectance, a UV/VIS spectrophotometer (UV-1800, Shimadzu Corp., Japan) was used to read absorbance on the filtrate from 400 to 700 nm with 1-nm increments. Four absorbance readings were taken on each cooked ground chicken sample, and the absorbance data were converted to percentage reflectance using the equation described by Stewart et al. (1965). Nicotinamide hemochrome (rNIC) was estimated by the percent reflectance ratio of %R537 nm/%R553 nm, where a higher value indicates more pigments (Schwarz et al., 1998).

Representative fresh ground turkey samples from each replication and cooked products from each NaCl treatment with the different endpoint cooking temperatures were analyzed for residual nitrite by the method described by AOAC (2007). Nitrosyl hemochrome and total pigments were measured on cooked turkey samples after extraction in 80% acetone and acidified acetone (Hornsey, 1956). For nitrosyl hemochrome determination, 10 g of cooked turkey product was blended with 40 mL acetone and 3 mL distilled, deionized water using a homogenizer (Polytron PT10-35, Kinematica AG, Switzerland). The homogenized samples were kept in the dark for 15 min before absorbance measurement. The homogenate was filtered through a Whatman No. 1 filter paper, and absorbance of the filtrate at 540 nm (A₅₄₀) was determined using a spectrophotometer (Model UV mini 1240, Shimadzu Corporation, Japan). Nitrosyl hemochrome concentration (ppm) was calculated as: A₅₄₀×290. For total pigment measurement, 10 g of the cooked samples was blended with 40 mL acetone, 1 mL HCl, and 2 mL distilled, deionized water, kept in the dark at cold temperatures (2–3°C) for 1 h, and then filtered through a Whatman No. 1 filter paper. Absorbance was measured at 640 nm (A₆₄₀). The total pigment concentration (ppm) was calculated as: A₆₄₀×680.

The experimental design of this study was a split plot design, with the four NaCl concentrations (0%, 1%, 2%, and 3%) representing the whole plot factor and the four endpoint cooking temperatures (70°C, 75°C, 80°C, and 85°C) representing the split plot factor. The fixed effects for NaCl concentration and endpoint temperature and their interactions were performed using the PROC MIXED procedure of the SAS 9.4 software (SAS, 2012). Dependent variable means were separated (p<0.05) by pairwise comparisons using the pdiff option. The experiment was replicated thrice.

The average pH value of the raw ground chicken breast samples was 5.96 (SD=0.12). A representative sample of raw ground chicken for all three replicates contained 0.16 ppm residual nitrite (SD=0.04). These results were consistent with those of Jeong (2017), who reported that raw ground chicken breast had an average pH of 5.98 and 0.18 ppm of residual nitrite. Claus and Jeong (2018) also reported similar results for raw turkey breast meat.

NaCl concentration affected all dependent variables tested in this study, associated with color and pigment properties of cooked ground chicken breasts (Table 1).

The cooking yield was lowest in 0% NaCl treatment (p<0.05), and increased (p<0.05) as the NaCl concentration increased from 0% to 3% (Table 2). This is consistent with the results of Lopez et al. (2012), who found that cooking loss decreased as NaCl concentration increased in vacuum-tumbled broiler breast meat. These results suggested that the addition of NaCl increased the negative charge on the protein surface, which increases the water holding capacity (Sebranek, 2009).

The pH values of cooked ground chicken products decreased with NaCl concentration (p<0.05), but there were no significant differences (p>0.05) in pH values between products treated with 2% and 3% NaCl (Table 2). This result was similar to that of Puolanne et al. (2001), who found that the addition of NaCl reduced the pH of pork and beef sausages. Our results on the effect of salt on the pH of cooked chicken breast meat are also partially consistent with those of Jeong (2017), who reported that the pH of cooked chicken breast meat was not affected by varying the salt level from 0 to 3%.

The ORP of meat affects its color through the formation of hemochromes, which is promoted by reducing conditions (Cornforth et al., 1986) and strong reducing conditions are also essential for the formation of a stable pink color in cooked meats (Cornforth et al., 1991). Therefore, measuring ORP is important for investigating the color characteristics. In this study, ORP was found to be lowest (p<0.05; most reducing condition) in cooked ground chicken products without salt (0% NaCl).

As the concentration of NaCl increased in the ground chicken breast, the ORP also increased (p<0.05) (Table 2). This result was in contrast with that of Ahn and Maurer (1989b), who reported that ORP decreased upon the addition of salt in ground turkey meat. This disagreement may be related to differences in the pH values in the two studies. Higher pH has been shown to promote reducing conditions (Antonini and Brunori, 1971; Claus and Jeong, 2018). Samples without NaCl had the highest pH values, resulting in the most negative ORP values. In addition, there were no significant differences in the pH of samples treated with 2% and 3% NaCl (Table 2). Jeong (2017) found that cooked ground chicken breasts with 0, 1, 2, or 3% NaCl had similar ORP values, when they were stored for 3 d before cooking, although these values tended to slightly decrease with increasing NaCl concentrations.

Residual nitrite contents in cooked ground chicken breasts were found to increase (p<0.05) with increasing NaCl concentrations (Table 2). It seems likely that NaCl caused the increase of residual nitrite (Ahn and Maurer, 1989a). However, the detected levels of residual nitrite contents ranged from 0.26 to 0.56 ppm across all samples in this study. These values were not sufficient to develop a pink color in meat products, as reported by previous researches (Ahn and Maurer, 1989a; Heaton et al., 2000). Ahn and Maurer (1989a) found that addition of 1 ppm nitrite resulted in a significant increase in the redness of turkey breast meat. Heaton et al. (2000) also reported that the minimum amount of nitrite for detecting pinkness was 1.3 and 0.7 ppm for cooked turkey and chicken breast, respectively.

The myoglobin contents were reduced (p<0.05) by the addition of NaCl, with the exception of 3% NaCl. However, there was no significant difference (p>0.05) between the myoglobin contents in the samples treated with 1% and 2% NaCl (Table 3). This finding is consistent with that of Jeong (2017), who also reported a decrease in myoglobin content when salt concentration was increased from 0% to 2%, except for cooked chicken breasts with 3% NaCl. However, we found no significant differences in the myoglobin contents of samples treated with 1% and 2% NaCl (p>0.05). Samples treated with 3% NaCl had lower (p<0.05) myoglobin contents than those treated with 1% and 2% NaCl, but had similar myoglobin content (p>0.05) as the samples without NaCl. The effects of salt on the PMD contrasted with those on myoglobin content (Table 3). The addition of NaCl is known to destabilize myoglobin in meat products upon cooking, leading to greater heat denaturation (Ahn and Maurer, 1989c; Jeong, 2017; Min et al., 2009; Trout, 1989). Claus and Jeong (2018) reported that cooked ground turkey breasts with 2% NaCl had lower myoglobin contents and higher PMD than those without NaCl, regardless of the processing condition, which is similar to our results.

Both nitrosyl hemochrome and total pigment content was highest in samples without NaCl (p<0.05), although no significant difference (p>0.05) was observed between the samples treated with NaCl (Table 3). Ahn and Maurer (1989a) reported that the addition of NaCl reduced the nitrosyl hemochrome and total pigment in turkey meat treated with nitrite, which is consistent with our results. Jeong (2017) also obtained similar results for cooked ground chicken breasts when ground meat was presalted (0-3% salt) and stored for 3 d before cooking.

The CIE L* values decreased with increasing NaCl concentration (p<0.05). The CIE a* value was lower in samples treated with 3% NaCl (p<0.05) than in the others. However, samples treated with 0%, 1%, and 2% NaCl had similar (p>0.05) CIE a* values in cooked chicken breasts (Table 4). Holownia et al. (2003) reported that pink color can be detected when a* value is more than 3.8 in chicken breast meat. In this study, CIE a* values of samples treated with 1% and 2% NaCl were 4.08 and 3.83, respectively. Therefore, the pink color was developed without any pink-generating ligands in cooked ground chicken breasts. In addition, Claus and Jeong (2018) demonstrated that the storage of ground turkey in the presence of 2% NaCl, rather than without salt, promoted the formation of pink pigments. Although the absence of salt in ground chicken meat was tested in this study, the average CIE a* value of these samples was 3.67, which was similar to those of the samples treated with 1% and 2% NaCl (Table 4). The CIE b* values were highest (p<0.05) in the samples without NaCl, and tended to decrease (p<0.05) with increasing NaCl concentration (Table 4). No significant differences (p>0.05) were observed in the CIE b* values of samples treated with 1% and 2% NaCl. The samples treated with 3% NaCl showed higher (p<0.05) CIE b* values than those treated with 1% and 2% NaCl. Ahn and Maurer (1989a) reported that, when 2% NaCl was added to turkey breast, the L* value decreased and a* value increased, which is consistent with our results. The addition of more than 3% NaCl may reduce the redness of cooked products by promoting oxidative conditions and denaturing myoglobin (Jeong, 2017; Rhee and Ziprin, 2001; Trout, 1989), and this could explain the decrease in the CIE a* value of samples treated with 3% NaCl in this study.

Nicotinamide can form strong heme complexes with myoglobin and hemoglobin (Ahn and Maurer, 1990b), and is responsible for producing the pink color (Cornforth et al., 1986; Claus et al., 1994). In this study, the rNIC ratio (ratio of %R537 nm/%R553 nm) was measured as an indicator of nicotinamide hemochrome. The rNIC ratio of the cooked ground chicken products was increased (p<0.05) when 1% NaCl was added, but decreased with higher concentrations of NaCl (p<0.05; Table 4). The rNIC ratio of samples treated with 2% NaCl was not different (p>0.05) from those not treated with NaCl. Samples treated with 3% NaCl showed the lowest rNIC ratio. Overall, the rNIC showed a trend similar to the CIE a* values in current study. These results indicate that nicotinamide hemochrome may contribute to the development of pink color in fully cooked ground chicken breasts without the addition of pink-generating ligands, if the ground meat is presalted and stored for 7 d before cooking.

The endpoint cooking temperature had limited effects on the color and pigment properties of cooked ground chicken breasts (Table 1).

As expected, the cooking yield decreased as the endpoint cooking temperature increased (p<0.05), but there were no differences (p>0.05) between the samples cooked to 70°C and 75°C (Table 5). Murphy and Marks (2000) found that cooking loss in chicken breasts patties increased as the cooking temperature increased from 23°C to 80°C, which is similar to our results.

The pH values ranged from 6.14 to 6.15 across all cooked products and there were no differences (p>0.05) in the pH values, regardless of internal cooking temperatures (Table 5). A similar finding was reported by Claus and Jeong (2018) for ground turkey breast products cooked to 71.1°C, 73.9°C, 76.7°C, and 79.4°C. Generally, the pH value affects the PMD, and increasing the pH may cause incomplete denaturation of myoglobin, forming a pink hemochrome in turkey breast and bratwurst (Trout, 1989; Ghorpade et al., 1992), which can lead to increased redness (Davis and Franks, 1995). Thus, consistent pH values at different cooking temperatures may not have influenced myoglobin denaturation and redness in this study.

As endpoint cooking temperature increased, the ORP also increased (p<0.05; Table 5). Cornforth et al. (1986; 1991) found that pink color developed under reducing conditions. In cooked meat, globin denaturation could cause the exposure of heme, and heme iron is oxidized rapidly by air exposure; thus, relatively strong reducing conditions are necessary to form stable pink complexes (Cornforth et al., 1991).

Residual nitrite contents were generally increased with cooking temperature. When samples were cooked at 80°C and 85°C, the residual nitrite contents were higher than when samples were cooked at 70°C. However, no differences (p>0.05) in residual nitrite contents were found between samples cooked at 75°C and 85°C. Ahn and Maurer (1987) reported that at least 1 ppm of nitrite is required to develop pink color in turkey meat. In this study, as residual nitrite content ranged from 0.40 to 0.46 ppm, it is considered that the residual nitrite content did not affect the color and pigment characteristics of cooked chicken breasts.

No differences (p>0.05) were observed in myoglobin contents and PMD for any of the endpoint cooking temperatures tested (Table 6). Similar results were reported by Ghorpade and Cornforth (1993); when pork meat was heated to final internal temperatures of 65°C and 82°C, myoglobin content and PMD was found to be not affected by the cooking temperature.

Further, the endpoint cooking temperature did not affect nitrosyl hemochorme and total pigments (p>0.05; Table 6). Claus and Jeong (2018) obtained similar results in ground turkey breasts cooked at different internal temperatures.

The CIE L* values tended to increase at high cooking temperatures (p<0.05), but there were no differences between the samples cooked to 80°C and 85°C (p>0.05). Similarly, the CIE b* values increased (p<0.05) with cooking temperature (Table 7). In contrast, the CIE a* values were similar (p>0.05) in all cooked samples, regardless of the cooking temperature (Table 7), although they decreased with cooking temperature. Davis and Franks (1995) reported that high endpoint cooking temperatures reduced redness, but increased lightness and yellowness in broiler thigh meat. Helmke and Froning (1971) found that lightness was increased, but redness and yellowness were decreased, as temperature increased from 60°C to 82°C in turkey meat, which was partially different from our results.

The rNIC ratio of cooked ground chicken breast samples showed significant difference (p>0.05) among the different treatments. Cornforth et al. (1986) reported that reduced globin or nicotinamide hemochromes could cause the pink color in cooked turkey rolls and that the pigments could be promoted by reducing conditions. Further, high cooking temperatures could lead to a more reducing environment in meat, which is more favorable for the formation of pink hemochromes such as nicotinamide hemochrome (Claus et al., 1994; Ghorpade and Cornforth, 1993; Hamm and Hofmann, 1965; Trout, 1989). However, in our study, the inherent levels of nicotinamide present in ground chicken meat did not affect the rNIC ratio, regardless of the cooking temperature.

Interaction effects between NaCl concentration and endpoint cooking temperature were found on cooking yield (p<0.0001) and total pigments (p<0.05) in cooked ground chicken breasts (Table 1). As expected, the cooking yield was lowest (p<0.05) in the samples without NaCl and cooked to 85°C (Table 8). The cooking yield decreased (p<0.05) as the cooking temperature increased. In general, the cooking yield from poultry products has been shown to be decreased when cooking temperature is increased (Claus and Jeong, 2018; Sammel and Claus, 2003; Slesinski et al., 2000b). However, higher levels of NaCl in ground chicken breast had little effect on the cooking yield at the different endpoint temperatures (Table 8). Samples cooked to 85°C had lower (p<0.05) cooking yield than those cooked to lower temperatures.

In samples without NaCl, the total pigments increased (p<0.05) with increasing cooking temperatures. However, samples treated with NaCl did not show significant differences (p>0.05) in total pigments when cooked to different temperatures. Furthermore, when the samples were cooked to 70°C and 75°C, there were no significant differences (p>0.05) in total pigments depending on NaCl concentration. However, the total pigments was higher in samples without salt (0% NaCl) than in those with salt (1%, 2%, and 3% NaCl) when cooked to 80°C and 85°C (p<0.05).