Quality of chicken breast meat cooked in a pilot-scale radio frequency oven

Innovative Food Science and Emerging Technologies 14 (2012) 77–84

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Quality of chicken breast meat cooked in a pilot-scale radio frequency oven Bilal Kirmaci, Rakesh K. Singh ⁎ Department of Food Science and Technology, University of Georgia, 100 Cedar Street, Athens GA 30602-2610, USA

a r t i c l e

i n f o

Article history: Received 19 January 2011 Accepted 14 January 2012 Editor Proof Receive Date 14 February 2012 Keywords: Radio frequency Poultry Shear values Marination Meat quality

a b s t r a c t Radio frequency (RF) cooking was compared to water bath (WB) cooking in terms of heating rate, temperature distribution, and the quality of cooked meat. Packaged fresh and marinated chicken breast meat were cooked in a continuously moving belt RF oven at 27.12 MHz until the center of the meat reached to 74 °C at the coldest point of the package. The time to reach end point temperature in the RF oven was 23.8 min for 1.36 kg packages, whereas it took 41.3 min to cook in the WB. RF cooking time was 42.4% lower than WB cooking time. Despite RF cooking resulting in a higher heating rate, better temperature distribution was observed for WB cooked breasts. Cook yield, moisture content, pH, expressible moisture, and shear value of RF and WB cooked meats were similar. However, RF cooked meat had lower a* (redness) and higher hue angle values than their WB cooked counterparts. Marination increased the cook yield, moisture content, tenderness, and pH value. Addition of ι-carrageenan to the marinade further increased the cook yield, moisture content, and tenderness of the cooked breasts. Neither marination nor addition of ι-carrageenan affected the expressible moisture of cooked meat. Industrial relevance: We have conducted our experiments in a pilot-scale RF oven. This machine is designed for the use of food industry and has 6 kW power. We have tried to find out another application of this machine, therefore we have established a procedure to cook chicken breast meat in the RF oven. Our experimental design might be the starting point for the food industry to develop this cooking process. While planning this research, we thought that pre-cooked and packaged chicken breast meat will be a good option for the restaurants to deal with the food safety regulations and foodborne illness outbreaks. Furthermore, this will lower their cost, which food industry will also take advantage of. © 2012 Elsevier Ltd. All rights reserved.

1. Introduction In the 1980s, whole broiler sales accounted for half of the poultry market, while the share of further processed broilers was only 10%. However, in the last 20 years, the demand for further processed poultry products has sharply increased to about 48% (NCC, 2009). Precooked, packaged chicken breast meat is served to customers with gravy or sauce in many restaurants. This ensures the food safety of the cooked chicken breast meat and the cost. The packaged meat can be either cooked by the conventional heating where heat transfer occurs by convection and conduction from a hot medium to the product, or by volumetric heating using electromagnetic radiation. Unlike conventional heating, volumetric heating is observed in the radio frequency (RF) and microwave (MW) heating systems by generation of heat inside the product due to the electromagnetic field (Brunton et al., 2005). Radio frequencies used for heating are limited to 13.56, 27.12 and 40.68 MHz in order to prevent interference with communication systems (Piyasena, Dussault, Koutchma, Ramaswamy, & Awuah,

⁎ Corresponding author. Tel.: + 1 706 542 2286; fax: + 1 706 542 1050. E-mail address: [email protected] (R.K. Singh). 1466-8564/$ – see front matter © 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.ifset.2012.01.003

2003). The microwave frequencies approved for heating are 915 and 2450 MHz for industrial and home use, respectively. In RF heating, a food product is placed in between two electrodes where an electromagnetic field is created by conversion of electric energy. Movement of positive ions to the negative regions and negative ions to the positive region (ionic depolarization) causes heating when electromagnetic field is applied at RF wavelengths (Marra, Zhang, & Lyng, 2009). This mechanism is also valid in the MW heating in addition to the dipole rotation, which refers to the alignment of dipole molecules according to the polarity of the electromagnetic field (Marra et al., 2009). RF heating depends on the dielectric properties of the foods, which is influenced by frequency, temperature, moisture content and composition (Marra et al., 2009; Piyasena et al., 2003). Longer wavelengths of RF with respect to microwaves (MW) provide higher penetration depth, which allows heating of thicker products, like chicken breast meat. Overcooking is avoided while energy is transferred by longer wavelengths. However, the risks of arcing and thermal runaway are the main problems that limit the use of RF heating in the food industry (Zhao, Flugstad, Kolbe, Park, & Wells, 2000). However, RF cooking of ham, pork, ground and comminuted meat products, and turkey breast meat has been studied and compared to the conventionally cooked counterparts (Brunton et al., 2005; Laycock, Piyasena, & Mittal, 2003; Zhang, Lyng, & Brunton, 2004; Zhang, Lyng, & Brunton, 2006).

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In recent years, marination, a culinary technique is used to meet consumer expectations by tenderizing the meat as well as improving the juiciness of the chicken breast meat. Salt and phosphates, such as sodium tripolyphosphate (STPP) are the primary ingredients of the marinade that tenderize the meat by unfolding the proteins due to shifting the pH further away from the isoelectric point of proteins (Lemos, Nunes, & Viana, 1999). Marinades can be enhanced by secondary ingredients such as hydrocolloids, water binders, flavor enhancers and antimicrobials to increase functionality (Alvarado & McKee, 2007). Marination also increases the cook yield of chicken breast meat (Qiao, Fletcher, Smith, & Northcutt, 2002; Zheng, Toledo, & Wicker, 1999). Furthermore, ι-carrageenan, a seaweed extract and a hydrocolloid, retains the water in the structure, resulting in higher juiciness in the foods. The purpose of the study was twofold. Firstly, a RF protocol for chicken breast meat was developed. Secondly, the quality of the cooked chicken breast meat by conventional and RF methods was assessed. Furthermore, effects of marination and addition of ι-carrageenan on the quality of cooked chicken breasts were also studied up to 1 month storage at 4 °C. 2. Materials and methods 2.1. Overall procedure Flow diagram of the cooking process is given in Fig. 1. Preliminary studies included selection of type of packaging material, heating medium and determination of distance between electrodes. RF cooking procedure was built based on the preliminary experiments, and then quality parameters were analyzed. In subsequent sections, details are given. 2.1.1. Chicken breast meat preparation Six batches of 9 kg boneless skinless fresh chicken breast meat were obtained from a local poultry processing plant (Mar Jack Inc., Gainesville, GA). Each batch of chicken breast meat was refrigerated at 4 °C for 2 to 24 h, and then processed in a 7 °C processing room. Five different treatments were investigated to determine the efficiency of cooking. Each treatment was replicated from different batches. Chicken breast meat was marinated in a vacuum tumbler except in the first treatment (Fresh) that was packaged immediately after removal from cold storage. Marinade solutions were prepared in the Meat receiving Quality

Marination

analyses Thermocouple insertion Packaging

Radio frequency

Water bath

cooking

cooking

Storage

Quality

Storage

Quality

at 4 °C

analyses

at 4 °C

analyses

Quality

Quality

analyses

analyses

following the order: water, STPP, and salt. Four treatments were prepared to give the following concentration in the final products: 1% salt and 0.3% STPP. Two treatments (M15-G and M20-G) contained an additional 0.25% (w/w final product) semi refined ι-carrageenan (S-100Fi, Ingredient Solutions Inc., Waldo, ME). Composition of marinade solutions and uptake of each treatment are given in Table 1. 2.1.2. Packaging and temperature measurement Marinated or unmarinated fresh chicken breast meat was packaged in 1.36 kg (3.00 lb) and 2.27 kg (5.00 lb) retortable packages (Sealed Air Corp., Duncan, SC), under 93.3 kPa vacuum by a vacuum sealer (Henkelman, Hertogenbosch, Netherlands). Retortable packages were composed of three layers, 12 μm polyethylene terephthalate (PET) coated with aluminum oxide, 25 μm biaxially oriented nylon (BON) and 100 μm retortable cast polypropylene (CPP). Package dimensions were 28 × 29.2 × 2.3 cm 3, and 36.8 × 29.2 × 2.8 cm 3, for 1.36 kg and 2.27 kg respectively. The packages were then stored in a 4 °C cooler for 0–3 h, and placed in the RF oven or water bath (WB) for cooking experiments. Fiber optic temperature probes (Fiso Tech. Inc., Quebec, Canada) were used to monitor the temperature during the RF cooking. The temperature of breast meat in the WB cooking was monitored by thermocouples (type K, Fisher Scientific, Pittsburgh, PA). A hole was made on one side of the pouches by a #5 brass cork borer. Then, a stuffing box (C-5.2D, Eucklund-Harrison Tech., Fort Myers, FL) was placed on the pouches, so that either fiber optic cable or thermocouple could be inserted into the package. 2.1.3. RF system All treatments were cooked in the RF oven (Model S061B Strayfield Ltd, Reading, UK) operating at 27.12 MHz frequency. The RF oven consists of a RF generator, two electrodes, and a conveyor belt. The product and container were placed in between the upper and lower electrodes. The upper electrode was built in such a way that the distance between the two electrodes was adjustable. Since cooking was done in batches, the conveyor was turned off. The power output of the RF oven was adjusted to 6 kW. 2.1.4. RF cooking protocol Based on preliminary experiments, the individual packages were placed in two high density polyethylene trays, which were used for cooking 1.36 kg and 2.27 kg meats. Dimensions of the trays were 39.4 × 34.3 × 6 cm 3 and 43.8 × 36.2 × 6 cm 3 for 1.36 and 2.27 kg packages, respectively. Reverse osmosis (RO) filtered water at 20 °C was added to the container until the water level reached to half the height of the container. After placing the fiber optic temperature probe at the bottom of package, a customized grid was inserted on top of the container to hold the package. The grids were manufactured such that they were allowed to touch the package along its length only. Dimensions of the grids for the larger containers were 40.6 × 0.95 × 2.54 cm 3 and 38.1 × 0.95 × 0.95 cm 3. Dimensions of the grids for the smaller container were 38.4 × 0.95 × 2.54 cm 3 and 34.3 × 0.95 × 0.95 cm 3. Table 1 Marinade composition and weight uptake. Treatment

Salt (%) STPP (%) Carrageenan (%) Marinade uptake (%) a b c d

Fig. 1. Flow diagram of the cooking chicken breast meat.

e

Fresha

M15b

M15-Gc

M20d

M20-Ge

– – – –

7.6 2.3 – 15

7.6 2.3 1.9 15

6 1.8 – 20

6 1.8 1.5 20

Fresh unmarinated chicken breast meat (CBM). M15 marinated CBM with 15% weight gain. M15-G marinated CBM with 15% weight gain and ι-carrageenan. M20 marinated CBM with 20% weight gain. M20-G marinated CBM with 20% weight gain and ι-carrageenan.

B. Kirmaci, R.K. Singh / Innovative Food Science and Emerging Technologies 14 (2012) 77–84

After the container was filled with RO water, it was placed between the electrodes of the RF oven. Then the electromagnetic field was applied to the package immersed in water. The distance between the electrodes was adjusted such that the anode current flow was 0.7 A. The RF oven was turned off when the temperature at the center of the chicken breast meat reached 74 °C. The packages were opened immediately to obtain the temperature profile of cooked chicken breast meat. A type K thermocouple was also used to measure temperature of cooked chicken breast meat after cooking in RF to confirm the temperature measured by the fiber optic probes. The cooked meat was cooled down to room temperature (21 °C) before measuring the quality attributes. 2.1.5. Water bath cooking protocol Only fresh, M20 and M20-G conditioned chicken breast meats were cooked in the WB (Temptronic 100, Thermolyne Corp., Dubuque, IA) with circulating water at 80 °C. The M15 and M15-G conditioned chicken breast meats were not cooked in the WB. Aside from the fresh chicken breast meat, only the 1.36 kg packages were cooked in the WB since similar results from cooking in 1.36 kg and 2.27 kg packages were expected. Chicken breast meat was cooked to a core temperature of 74 °C. The temperature profiles of cooked chicken breast meat were determined immediately. Finally samples were cooled down to 21 °C before conducting quality control analyses. 2.1.6. Sample preparation and storage One breast from raw and marinated chicken breast meats was packaged and refrigerated at 4 °C. Eighteen cooked chicken breast meat strips of 1.9 cm wide were cut from randomly selected chicken breast meats. One third of cut strips were analyzed at day zero, and the remaining strips were packaged in a plastic pouch (Packall Packaging Brampton, ON, Canada) under vacuum with a vacuum sealer (Henkelman, Hertogenbosch, Netherlands). Packaged strips were stored for 7 and 30 days in the cooler at 4 °C. Analyses were conducted when the temperature of the strips reached 21 °C. Color, moisture content, pH, expressible moisture, and texture analysis were done. 2.2. Moisture content Moisture contents of fresh, uncooked marinated, and cooked chicken breast meats were determined in duplicate according to the Association of Official Analytical Chemists (AOAC, 1995). About 3.0–3.5 g samples were placed in appropriate pre-dried aluminum pans (Fisher Scientific, Pittsburgh, PA) and dried in a vacuum oven (Cole-Parmer Instrument Co., Vernon Hills, IL) at 10.7 kPa pressure and 99 °C for 24 h. 2.3. pH value The pH values of fresh, marinated and cooked chicken breast meats were measured in triplicate according to a direct probe method. A pH meter (Accumet AR15, Fisher Scientific, Pittsburgh, PA) was used with a flat meat surface probe (Accumet, Fisher Scientific, Pittsburgh, PA). The probe of the pH meter was calibrated using pH 4.00 and pH 7.00 buffer solutions (Fisher Scientific, Pittsburgh, PA). 2.4. Cook yield Cook yield was determined based on the original weight (green weight) of fresh chicken breast meat. As previously described, cooked meat was cooled down to room temperature (21 °C) and weighed. Cook yield was calculated as follows: % Cook yield ¼ ðCooked weight=Initial green weightÞ  100:

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2.5. Expressible moisture The expressible moisture was measured in duplicate according to the filter press method as described by Wierbicki and Deatherage (1958). Samples having 19 mm fixed diameter and 300 ± 10 mg weight were obtained from fresh, marinated and cooked chicken breast meats using a #12 brass cork borer. The sample was placed on a pre-weighed Whatmann filter paper (no.1, 9 cm) between two Plexiglass plates and compressed by a 1.0 kg load cell for 1 min. After 1 min, the filter paper was weighed to determine the amount of water released from the sample. Expressible moisture was calculated: Expressible Moisture ðEMÞ ¼ 100  ðWfinal −Winitial Þ=sample weight where; Wfinal ¼ weight of filter paper after compression Winitial ¼ initial weight of filter paper:

2.6. Warner–Bratzler shear test Warner–Bratzler shear test (WBS) was performed on the cooked chicken breast meat, as described by Deshpande (2008). Shear force was determined using a Texture Analyzer (TA-XT2i, Texture Tech. Corp., Scarsdale, NY) with a 25-kg load cell using a shearing blade (TA 7-WB blade). As described, six cooked chicken breast meat strips (1.9 cm wide) were cut to 2.5 cm long and 2.0 cm thick samples. The samples were placed on a slotted plate which was installed into a heavy-duty platform (TA 90). The platform was adjustable to allow the blade to pass through the slotted plate. The crosshead speed was set at 10 mm/s, and the test was triggered by a 0.05 N contact force. The pre- and post-test speeds were set to 5 mm/s. Shear force was calculated as area under the force deformation curve by the texture analyzer. Shear value was reported as mean of six replicates for each cooking condition. 2.7. Color The surface color of cooked chicken breast meat was determined by a chroma meter (Model CR-300 Minolta, Ramsey, NJ). Lightness (L*), a* (redness/greenness), b* (yellowness/blueness), chroma (saturation) and hue angle (H°) were determined. The measurements were reported as mean of six chicken breast meat strips for each cooking treatment. A standard white plate was used to calibrate the color measurement. 2.8. Statistical analysis Experiments were conducted according to an incomplete randomized block design, since the main objective of this study was comparison of RF cooking to WB cooking. The experimental design was not a full factorial design because the WB cooked samples were considered controls. The general linear model was used to analyze data. Treatment means were separated by the least square means using the Tukey's test at 95% confidence level (Minitab V.15.0, Minitab Inc., State College, PA). 3. Results and discussion 3.1. Uncooked chicken breast meat Results of moisture content, expressible moisture, and pH analysis of fresh and marinated uncooked chicken breast meat are given in Table 2. As expected, the total moisture content of the marinated chicken breast meat was higher than that of fresh chicken breast meat. It was observed that moisture content of the raw chicken breast meat varied by the lot. To eliminate this error, moisture content of fresh chicken breast meat was subtracted from that of marinated chicken breast meat and the differences were statistically analyzed

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Table 2 Moisture content, expressible moisture and pH of uncooked chicken breast meat. Treatment

Fresh M15 M15-G M20 M20-G a b

Raw

Marinated

MCa (%)

EMb (%)

pH

MC (%)

EM (%)

pH

75.61 ± 0.4 75.32 ± 0.7 76.02 ± 0.3 75.98 ± 0.6 76.32 ± 0.6

15.71 ± 2.2 14.07 ± 2.1 15.37 ± 1.3 14.70 ± 1.8 16.73 ± 2.3

5.84 ± 0.07 5.96 ± 0.14 6.02 ± 0.06 5.92 ± 0.08 5.97 ± 0.09

n/a 76.16 ± 0.5 76.13 ± 0.2 77.10 ± 0.9 78.87 ± 1.3

n/a 11.39 ± 3.0 10.96 ± 1.7 11.57 ± 2.4 12.71 ± 2.2

n/a 6.04 ± 0.10 6.01 ± 0.11 6.02 ± 0.07 6.05 ± 0.09

MC: moisture content. EM: expressible moisture.

(Table 3). Moisture content of fresh chicken breast meat was determined to be 76.12 ± 0.2%. Marination resulted in significant increase in the moisture content of chicken breast meat except in M15-G conditions. The highest increase in moisture content was observed in M20-G conditions (p b 0.05). Furthermore, level of marination also did not affect the moisture content of breast meats (p > 0.05). All marinated chicken breast meat had lower expressible moisture value than the fresh chicken breast meat (p b 0.05). This result shows that free water (unbound water) of the raw chicken breast meat was retained by meat protein structure, ι-carrageenan or their interaction. Inclusion of hydrocolloid at the same marination level did not affect the expressible moisture (p > 0.05). Even though ι-carrageenan is insoluble in cold water, it swells during the tumbling process. Nevertheless, swelling of ι-carrageenan did not result in low expressible moisture value at the same marination level. Marination levels also did not affect expressible moisture significantly. It might be related to having the same concentration levels of salt and STPP in the final product in both, 15% and 20% uptake in the marinated chicken breast meat. The pH value of raw chicken breast meat varied between lots (5.87–6.03). Storage of some raw chicken breast meat for 1 day prior to cooking or unequal aging of chicken breast meat at the processing plant might be the reasons for the variation. To neutralize that error term, the pH difference between marinated and raw chicken breast meat was analyzed (Table 3). Mean pH value for raw chicken breast meat was determined as 5.98± 0.03 within the range of reported pH values 5.81–6.12 (Qiao et al., 2002; Zheng et al., 1999). Results showed that the marinated chicken breast meat at 20% uptake (M20 and M20-G) had significantly greater pH value than the raw meat. However, there was no significant difference in pH values at 15% marinade uptake (M15 and M15-G) and the pH of raw chicken breast meat. Despite the fact that the aim of marination is to shift the pH toward basic pH, results did not show the expected rise in pH values of chicken breast meat after marination. Mean pH value for marinated chicken breast meat was 6.02, which is very close to the 6.03 reported by Qiao et al. (2002), and lower than 6.81 reported by Zheng et al. (1999). Inclusion of ι-carrageenan did not affect the pH value at the same marination level (p > 0.05). Since semi refined ι-carrageenan has almost neutral pH, those results were expected. Table 3 Difference in moisture content, expressible moisture and pH values between raw and marinated uncooked chicken breast meat. Treatment

M15 M15-G M20 M20-G

Difference ΔMC1

ΔEM2

ΔpH3

0.84ab ± 0.8 0.11a ± 0.2 1.12b ± 1.2 2.55c ± 1.0

− 2.68 ± 3.3 − 4.41 ± 1.9 − 3.13 ± 3.3 − 4.01 ± 2.9

0.05ab ± 0.10 0.02a ± 0.10 0.10b ± 0.11 0.07ab ± 0.09

Different letters in the same column show significant difference (p b 0.05). 1 ΔMC = MC of marinated chicken breast meat – MC of raw chicken breast meat. 2 ΔEM = EM of marinated chicken breast meat – EM of raw chicken breast meat. 3 ΔpH = pH of marinated chicken breast meat – pH of raw chicken breast meat.

3.2. Preliminary study for RF cooking Heating rate of products in the RF depends on several parameters such as dielectric properties of product, heating medium, anode and grid current. Anode and grid current were adjusted by changing the distance between the upper and lower electrodes. Anode current can be increased to maximize heating by decreasing the distance between the electrodes. However, decreasing the distance increases the risk of arcing. In the preliminary studies, packages were easily melted due to high anode current above 0.7 A. Therefore, cooking was done at that current. Nevertheless, it was difficult to control the current when the water temperature increased above 95 °C. The distance between electrodes was 9 cm in the beginning of the process. The distance was gradually increased until the water temperature reached 97 °C. Then a sharp increase in the distance was required to prevent arcing. However, the current was high enough to boil the water. RF generator was turned off for 1 min to cool down the water and then it was turned on again. The type of package was determined during preliminary experiments. Different types of packages such as, ovenable, retortable and cook-in-bags, from Sealed Air Corporation and Floeter Inc. (Elk Grove Village, IL) were used to select the most appropriate package. Parts of the ovenable and cook-in-bag packages melted during RF heating. Although, the packages composed of polyethylene terephthalate (PET) and cast polypropylene (CPP) were very durable for cooking, it was not possible to use them due to the size limitation. Preliminary experiments showed much better results for retortable pouches. The heating medium was also studied during the preliminary experiments. Initially, the heating was done with the air medium around the breast meat, so that the heating rate of product would be high. However, the arcing and melting of the packages made it impossible to cook in the air medium. Brunton et al. (2005) also reported failure to cook comminuted pork meat product in air using an RF oven. Water immersion cooking was suggested to avoid the arcing problem. Although sufficient amount of water was added into the tray, some parts of the package floated out of the water, and RF energy melted that area of the package when the temperature of the product reached around 50 °C. This ballooning effect was due to the expansion of vapor generated inside the packages. In order to prevent packages from floating, customized parallel spacers, made from polyetherimide, were attached to the top of the container. Even though it delayed arcing, the problem could not be completely solved. A polyetherimide plate was placed under the spacers covering the package surface to prevent interaction between electromagnetic energy and the package. Despite very high heating rate of water, heat was transferred to the product by convection and conduction only. Hence, a slow heating rate of product was observed. Melting of package was again observed when the temperature of the plate rose. Finally, a grid was manufactured from polyetherimide instead of covering the whole package with a plate. Trays integrated with customized grid were able to hold the packages under water throughout the RF cooking.

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Fig. 2. Typical temperature–time history of radio frequency and water bath cooking of marinated chicken breast meat with 20% weight gain (M20).

3.3. RF cooking RF oven was turned off once during the cooking of Fresh, M20 and M20-G conditioned chicken breast meats, whereas during cooking of M15 and M15-G conditioned chicken breast meat it was turned off twice. A considerable amount of water evaporation was observed during cooking experiments. In several experiments, arcing occurred at the end of the process. Despite developing the RF cooking protocol, arcing occurred either on the container or the grid instead of the package. Even though arcing was observed in some experiments, all the cooked chicken breast meat packages were free of melting or any indication of burning. Results showed that RF cooking of chicken breast meat had higher heating rate than WB cooking. Average heating rate of chicken breast meat was 2.67 °C/min during cooking in the RF oven, while it was 1.8 °C/min for WB cooking. Typical time–temperature graphs for RF and WB cooking of M20 conditioned 1.36 kg chicken breast meat are given in Fig. 2.

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the RF oven, the cooking time was significantly lower in the RF oven cooking than the WB cooking in both size of packages. In contrast to cooking method and package size, neither marination level nor inclusion of hydrocolloid altered the cooking time significantly. Addition of salt due to marination changed dielectric properties of chicken breast meat except the dielectric constant. Dielectric loss factor of fresh chicken breast meat was lower than that of marinated chicken breast meat, 415.2 and 967.8, respectively (Lee, Toledo, & Nelson, 2008). On the other hand, fresh meat had greater penetration depth of RF than the marinated meat, 11 cm and 8.3 cm, respectively (Lee et al., 2008). This could be the reason to get the same cooking time for fresh and marinated chicken breast meat. National Advisory Committee On Microbiological Criteria For Foods ([Anon] & Nacmcf, 2007) recommends cooking poultry products until its internal temperature reaches 74 °C. Therefore, endpoint temperature was selected as 74 °C at the coldest point of the package in both RF oven and WB. However, mean temperature of the RF cooked chicken breast meat was 79.3 ± 0.4 °C. On the contrary, WB cooked chicken breast meat had better temperature distribution with a mean temperature of 74.9 ± 0.08 °C. As heat is generated within the product in the RF oven, a more uniform temperature distribution was expected. Temperature of the cooked meat near to the edges and walls of the container was greater than that of the meat in the middle of the container (Fig. 3). This could be attributed to shape, edge or corner effect (Reuter, 1993). Edges of the container are usually exposed to more energy than the middle part of the container, as runaway heating occurs. In this study, the average temperature differential between RF cooked chicken breasts was 5.33 ± 0.4 °C, which was greater than temperature differential between WB cooked chicken breast, 0.9 ± 0.08 °C. A previous study reported RF cooked muscle beef had a 10 °C temperature differential within the different areas of muscle (Laycock et al., 2003). Tang, Cronin, and Brunton (2005) were able to decrease the temperature differential to 5.3 °C by circulating water during RF heating of turkey rolls.

3.4. Cooking time and temperature distribution 3.5. Cook yield RF cooking time was significantly lower than the WB cooking time (Table 4). The average time required to cook the 1.36 kg chicken breast meat in the RF was 23.8 min, about 42.4% lower than the time required for WB, 41.3 min. Tang et al. (2005) cooked the turkey breast rolls in an RF oven for 40 min, while it took 150 min to cook it in a thermostatically controlled steam oven at 80 °C. In another study a 79% reduction in cooking time was achieved during cooking of a large diameter comminuted meat product (Zhang et al., 2004). As the mass of product increases by increasing the package size, the 2.27 kg chicken breast meat package required more time, 32.6 min, for cooking in the RF oven. It took 57 min for the same amount of chicken breast meat to cook in the WB. There was a 42.8% reduction in cooking time in RF with respect to WB cooking (p b 0.05). Even though WB had circulation of water advantage over

Cook yields of RF and WB cooked samples were not significantly different (Table 4). This is in agreement with the previously published research (Tang et al., 2005; Zhang et al., 2004). However, Laycock et al. (2003) reported higher cook yield for RF cooked samples than that of WB cooked samples. The inclusion of ι-carrageenan to marinade formula increased the cook yield (p b 0.05). The highest cook yield was achieved when M15-G and M20-G conditioned chicken breast meats were used. Mean cook yield of M20-G conditioned chicken breast meat was determined as 106.59% due to water binding effect of carrageenan. It was significantly greater than the cook yield of M20 conditioned chicken breast meat, as ι-carrageenan has the ability to retain large amount of water. In another study, addition of κ-carrageenan in the

Table 4 Cooking time, cook yield, moisture content, expressible moisture, pH value of RF and WB cooked chicken breast meat. Treatment

RF

WB

Cooking time (min)

Fresh M15 M15-G M20 M20-G Fresh M20 M20-G

1.36 kg

2.27 kg

20.5a ± 0.7 27.5a ± 0.7 24.5a ± 0.7 23.5a ± 0.7 23a ± 1.4 41b ± 1.4 41b ± 0.0 42b ± 1.4

28.75a ± 1.1 36.75a ± 7.4 30a ± 1.4 34a ± 1.4 33.5a ± 3.5 57b ± 0.7 n/a n/a

Different letters in the same column show significant difference (p b 0.05).

Cook yield (%)

Moisture content (%)

Expressible moisture (%)

pH

76.5a ± 2.3 92.5b ± 4.4 101.72c ± 1.6 95.98b ± 1.4 105.73c ± 2.9 77.48a ± 1.3 99.45b ± 0.2 107.45c ± 0.6

69.68a ± 1.2 71.68b ± 1.0 74.35cd ± 1.4 73.45c ± 1.5 74.76d ± 1.5 69.46a ± 0.9 74.11c ± 0.7 75.06d ± 1.6

10.51 ± 2.6 10.80 ± 3.4 10.84 ± 2.7 11.16 ± 3.5 11.31 ± 2.8 11.13 ± 1.9 11.21 ± 3.6 12.41 ± 1.9

6.13a ± 0.06 6.20bc ± 0.10 6.21bc ± 0.05 6.21c ± 0.06 6.24b ± 0.05 6.13a ± 0.07 6.19c ± 0.04 6.24b ± 0.03

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Fig. 3. Temperature distribution (°C) of radio frequency cooked marinated chicken breast meat with 20% weight gain and ι-carrageenan (M20-G).

low fat pork sausages resulted in lower cook loss (Lyons, Kerry, Morrissey, & Buckley, 1999) implying higher cook yield. Pietrasik (2003) reported that addition of κ-carrageenan improved the waterbinding properties of beef gels, so that cook loss was significantly decreased. Even though marination resulted in significant increase in the cook yield, the marination level did not affect the cook yield (p > 0.05). In fact, marinated chicken breast meats contained the same percentage of STPP and salt regardless of their marination level. 3.6. Storage, moisture content, expressible moisture and pH The quality analyses data were pooled for each storage period and statistically analyzed to determine the effect of storage. The treatments within the same storage period did not show any trend. Thus, the data were pooled to compare the effect of cooking methods on each quality parameter. In another study (Rozum & Maurer, 1997), cooked chicken breast meat stored for 5 weeks was investigated for microbial shelf life. They found that the microbial quality declined after 2 weeks of storage, but the microbiological analysis was not in the scope of this study. However, the other quality attributes in our study did not change over 4 weeks of storage. RF and WB cooking did not significantly affect the moisture content, expressible moisture and pH value of the samples (Table 4). ι-Carrageenan inclusion and marination level significantly increased the moisture content of cooked chicken breast meat. Although there was no difference between moisture content of cooked meat in M15-G and M20-G conditions (p> 0.05), M20 conditioned cooked meats had significantly greater moisture content than M15 conditioned cooked meats. The inclusion of ι-carrageenan increased the moisture content of cooked meat at the same marination level (pb 0.05). In fact, gelatinization and stability of carrageenan structure were established during cooling period after heating. Zheng et al. (1999) reported moisture content of cooked fresh and marinated chicken breast meat as 71.6% and 75.1%, respectively. In this study, mean moisture content of cooked fresh and marinated chicken breast meat was determined as 69.57% and 73.78%, respectively. Results showed that there was no significant difference among the expressible moisture content values of all samples. RF and WB cooking did not affect the expressible moisture significantly, which is similar to the results given for cooking of comminuted pork meat product

(Brunton et al., 2005). In another study, however, RF cooked ground beef and whole muscle meat products had better water holding capacity than WB cooked ground beef and whole muscle meat products (Laycock et al., 2003). Furthermore, Zhang et al. (2004) concluded that water holding capacity of RF cooked sample was better than that of steam cooked samples. Expressible moisture value results were the same for all conditions of chicken breast meat. In other words, neither marination level nor hydrocolloid inclusion to the marinade significantly affected the expressible moisture of cooked meat. In their study, Filipi and Lee (1998) expressed the same conclusion that pre-activated ι-carrageenan had no significant effect on expressible moisture of surimi gel, however, they indicated that dry ιcarrageenan significantly lowers the expressible moisture. In another study, expressible moisture values were the same for fresh and marinated chicken breast meat with different marinade formulations (Zheng, Detienne, Barnes, & Wicker, 2001). All marinated chicken breast meats had greater pH values than the fresh chicken breast meat after cooking (pb 0.05). Mean pH value for the marinated cooked chicken breast meat was determined as 6.24. Qiao et al. (2002) reported pH of 6.31 for cooked marinated chicken breast meat. Marination level and inclusion of hydrocolloid did not affect the pH value of cooked marinated chicken breast meat (p> 0.05).

3.7. Warner–Bratzler shear test Tenderness of chicken breast meat is an important quality parameter for consumer acceptability level (Cavitt, Meullenet, Xiong, & Owens, 2005) and WBS predicted the tenderness. Shear test results, given in Fig. 4, show very large standard deviations such as 17.79 ± 7.6 N for M15 conditioned meat. The main reason could be the random selection of samples from different locations within the packages and non-uniform temperature distribution of RF cooking as seen in Fig. 3. Cooking method did not significantly affect the shear value. Tang et al. (2005) also indicated no significant difference between texture profile of RF and steam cooked turkey rolls. In contrast, according to the research of Zhang et al. (2006) RF cooked leg and shoulder ham had higher Warner–Bratzler shear values than their steam cooked counterparts. Results showed that M15-G and M20-G conditioned chicken breast meat had the lowest shear values. Inclusion of ι-carrageenan decreased the shear value of cooked chicken breast meat at the same marinated level (p b 0.05). Moisture-binding ability of ι-carrageenan improved the succulence of chicken breast meat. Marinated chicken breast meat had lower shear value than the fresh chicken breast meat (p b 0.05), but marination level didn't significantly affect the shear value. Water binding capacity of chicken breast meat was improved by salt and phosphate. Concentrations of the salt and phosphate in the M15 and M20 conditioned chicken breast meats were the same. This may explain similar shear values for different

Fig. 4. Mean shear value of radio frequency ( ) and water bath ( ) cooked chicken breast meat.*Different letters show significant difference (p b 0.05).

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Table 5 Color parameters of RF and WB cooked chicken breast meat. Treatment RF WB

Hydrocolloid Control Hydrocolloid Control

L*

a*

b*

Saturation

Hue (°)

79.00 ± 1.8 79.31 ± 1.4 79.44 ± 1.7 79.65 ± 1.3

0.68a ± 0.7 0.90a ± 0.7 1.65b ± 0.6 1.49b ± 0.6

10.47a ± 1.2 12.31b ± 1.2 9.57a ± 0.7 12.23b ± 1.4

10.51a ± 1.1 12.35b ± 1.4 9.72a ± 0.7 12.33b ± 1.4

86.13b ± 4.2 85.77b ± 3.1 80.21a ± 3.5 83.03a ± 2.8

Different letters in the same column show significant difference (p b 0.05).

marination levels. Qiao et al. (2002) reported that the shear force value was not significantly correlated to the marination uptake level. 3.8. Color As the non-uniform temperature distribution was observed in the RF cooked samples (Fig. 3), the color parameters of them were different than that of WB cooked samples (Table 5). Redness and hue angle of the cooked chicken breast meat differed with respect to cooking methods (p b 0.05). RF and WB cooked chicken breast meat had the same lightness, yellowness and saturation values (p > 0.05). The RF cooked chicken breast meats had lower redness and higher hue angle values than their WB cooked counterparts (p b 0.05). It has been reported that an increase in the endpoint temperature of the water-cooked thigh meat decreased the redness (a*) due to more denaturation of myoglobin (Lyon, Loyn, Klose, & Hudspeth, 1975; Trout, 1989). Therefore, higher mean temperature of the RF cooked meat seems to be the reason to have lower redness and hue angle values. These results are in agreement with those of Tang et al. (2005) for turkey rolls. They indicated that RF cooked turkey rolls had the same lightness and yellowness values as the steam cooked rolls. On the other hand, lower redness values were observed for RF cooked turkey rolls. Laycock et al. (2003) reported that the RF and WB cooked ground and comminuted beef and whole muscle had the same lightness and redness values. In another study, no significant difference between L*, a*, b*, saturation, and hue angle values of steam, WB and RF cooked comminuted pork meat products was reported (Brunton et al., 2005). Barbut et al. (2005) reported the L* value of the WB cooked chicken breast meat as 79.73. In another study, L*, a*, and b* values of the steam cooked chicken breast meat were reported as 77.16, 1.69 and 10.14, respectively (Qiao et al., 2002). Whereas, Young and Lyon (1997) reported L*, a* and b* values of the WB cooked chicken breast meat as 78.7, 2.55 and 15.7, respectively. As inclusion of hydrocolloid changes the color of marinade, it might affect the L*, b* and saturation values of the cooked meat. Cooked chicken breast meat containing ι-carrageenan showed significantly lower yellowness and saturation values when compared to chicken breast meat which did not contain any hydrocolloid compound (Table 5). Moreover, inclusion of hydrocolloid to the chicken breast meat did not affect the lightness, redness and hue angle values (p > 0.05). 4. Conclusions The RF cooking of packaged fresh and marinated chicken breast meat was successfully carried out in the HDPE containers with the integration of a grid. Packages were immersed in water, as it was impossible to cook them in air due to the arcing problem. The high heating rate in the RF oven cooked the chicken breast meat in less time when compared to WB cooking. It took almost 24 min and 33 min to cook 1.36 kg and 2.27 kg chicken breast meat in the RF oven, respectively. The RF cooking compares favorably to conventional WB cooking which took substantially longer in both instances (41.3 min and 57 min). Even though rapid cooking was observed in RF cooking, temperature distribution of cooked meat was not as

uniform as that in WB cooking. Edge effect and thermal runaway were the main reasons for the observed variability in the mean temperature of the RF cooked meats. RF cooking resulted in 5.33 °C average temperature differential, whereas, it was 0.9 °C in WB cooking. Instrumental quality analysis showed that there were no significant differences between RF and WB cooked products with regard to cook yield, moisture content, pH, expressible moisture, shear value. Color measurements showed that L*, b*, hue values of the RF and WB cooked breast were statistically the same. However, RF cooked breasts had lower a* and saturation value, possibly due to non-uniform temperature distribution. Marination and addition of ι-carrageenan had positive effect on the cook yield, moisture content, and shear value of cooked chicken breasts. Meat with added hydrocolloid resulted in the more tender meat. The effect of marination and inclusion of hydrocolloid on the pH value of raw and cooked chicken breast meat could not be observed clearly. However, their effects on expressible moisture were insignificant. References [Anon], & Nacmcf (2007). Response to the questions posed by the food safety and inspection service regarding consumer guidelines for the safe cooking of poultry products. Journal of Food Protection, 70(1), 251–260. Alvarado, C., & McKee, S. (2007). Marination to improve functional properties and safety of poultry meat. Journal of Applied Poultry Research, 16(1), 113–120. AOAC (1995). Official methods of analysis (15th ed.). Washington, DC: Association of Official Analytical Chemist. Barbut, S., Zhang, L., & Marcone, M. (2005). Effects of pale, normal, and dark chicken breast meat on microstructure, extractable proteins, and cooking of marinated fillets. Poultry Science, 84, 797–802. Brunton, N. P., Lyng, J. G., Li, W. Q., Cronin, D. A., Morgan, D., & McKenna, B. (2005). Effect of radio frequency (RF) heating on the texture, colour and sensory properties of a comminuted pork meat product. Food Research International, 38(3), 337–344. Cavitt, L. C., Meullenet, J. F. C., Xiong, R., & Owens, C. M. (2005). The relationship of razor blade shear, Allo–Kramer shear, Warner–Bratzler shear and sensory tests to changes in tenderness of broiler breast fillets. Journal of Muscle Foods, 16(3), 223–242. Deshpande, D. (2008). Radio-frequency application in preheating of marinated chicken breast meat. MS Thesis. The University of Georgia, Athens, GA. Filipi, I., & Lee, C. M. (1998). Preactivated iota-carrageenan and its rheological effects in composite surimi gel. Lebensmittel-Wissenschaft und Technologie, 31(2), 129–137. Laycock, L., Piyasena, P., & Mittal, G. S. (2003). Radio frequency cooking of ground, comminuted and muscle meat products. Meat Science, 65(3), 959–965. Lee, H., Toledo, R., & Nelson, S. (2008). The dielectric properties of fresh and marinade chicken breast meat according to temperature rise from 1 to 70 °C. . Lemos, A., Nunes, D., & Viana, A. (1999). Optimization of the still-marinating process of chicken parts. Meat Science, 52(2), 227–234. Lyon, C. E., Loyn, B. G., Klose, A. A., & Hudspeth, J. P. (1975). Effect of temperature–time combinations on doneness and yields of water-cooked broiler thighs. Journal of Food Science, 40, 129–132. Lyons, P. H., Kerry, J. F., Morrissey, P. A., & Buckley, D. J. (1999). The influence of added whey protein/carrageenan gels and tapioca starch on the textural properties of low fat pork sausages. Meat Science, 51(1), 43–52. Marra, F., Zhang, L., & Lyng, J. G. (2009). Radio frequency treatment of foods: review of recent advances. Journal of Food Engineering, 91(4), 497–508. NCC (2009). How broilers are marketed. [WWW page]. : National Chicken Council http://www. nationalchickencouncil.com/statistics/stat_detail.cfm?id=7 Accessed on 18 January 2011. Pietrasik, Z. (2003). Binding and textural properties of beef gels processed with kappacarrageenan, egg albumin and microbial transglutaminase. Meat Science, 63(3), 317–324. Piyasena, P., Dussault, C., Koutchma, T., Ramaswamy, H. S., & Awuah, G. B. (2003). Radio frequency heating of foods: principles, applications and related properties — a review. Critical Reviews in Food Science and Nutrition, 43(6), 587–606. Qiao, M., Fletcher, D. L., Smith, D. P., & Northcutt, J. K. (2002). Effects of raw broiler breast meat color variation on marination and cooked meat quality. Poultry Science, 81(2), 276–280.

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