Physical and Chemical Attributes of a Ready-to-Eat Meat Product during the Processing: Effects of Different Cooking Methods

Abstract

The effects of cooking time (10–50 min) and treatments (atmospheric, pressure, and microwave cooking) on Kavurma (a ready-to-eat meat product) were investigated. Atmospheric and pressure cooking technique had more desirable quality attributes than microwave cooking technique on kavurma production. Color, texture, moisture content, pH, and 2-thiobarbituric acid reactive substance values were followed during processing. Moisture content, pH, 2-thiobarbituric acid reactive substance, hardness, and chewiness values of microwave cooked samples were significantly different (p < 0.05) than that of atmospheric and pressure cooked samples. The microwave cooking method had the greatest influence on lipid oxidation compared to others. While the level of 2-thiobarbituric acid reactive substance was lower which was under the threshold value of 1 mg MA/kg in atmospheric and pressure cooking, it was higher in microwave cooking. On the other hand, among Hunter color values, lightness value increased (p < 0.05) for atmospheric cooked samples while it decreased by time for pressure and microwave cooked samples. However, a* and b* values of microwave and pressure cooked samples were significantly higher than atmospheric cooked samples.

Keywords:

• Cooking methods
• Ready-to-eat meat product
• Kavurma
• Texture
• Color

INTRODUCTION

Kavurma, one of the important ready-to-eat meat products that is produced by the technique of cooking, is manufactured and consumed in Turkey, Greece, Germany, The Netherlands, and Middle Eastern countries.^[1,2] Kavurma has been produced for many years in homes and recently in modern plants since it is a very important ready to eat meat product having the highest shelf life and, therefore, satisfying the meat demand in every time. Salt (2–5%) and tailed fat are the main ingredients for kavurma production. Spices or other flavoring ingredients may be incorporated to the mixture while kavurma product is still warm. After that, it is filled into natural or artificial cases and stored under anaerobic conditions.^[2]

Cooking is the main process in kavurma production.^[2] Cooking causes several positive effects on meat, such as taste and flavor enhancement, inhibition of microorganism, increased shelf life, and improved digestibility.^[3] In this study, kavurma production was performed by three different techniques that are atmospheric, pressure, and microwave cooking. Atmospheric cooking is a traditional way of kavurma production. In this method, meat is cooked with all ingredients as uncovered, in hot air, in an oven.^[4] Pressure cooking is another technique for kavurma production. In pressure cooking, the steam that is produced by the boiling of liquid inside the meat builds up pressure. This caused to obtain higher cooking temperatures and shorter cooking times during the kavurma production.^[5] Vasanthi et al.^[6] indicated that the usual practice in Indian homes involves cooking meat in pressure cookers, cooking in water baths is also of significance and is believed to be a reliable method to optimize tenderness since this method of cooking ensures rapid and more consistent increases in the final internal temperature. Microwave cooking is caused by the ability of the materials to absorb microwave energy and convert it into heat. Microwave heating of food materials mainly occurs due to dipolar and ionic mechanisms. The presence of moisture or water causes dielectric heating due to the dipolar nature of water.^[7] This is because food with higher moisture content like meat will be heated up faster because of the dipolar interaction.^[8] However, this may cause some deteriorative reactions in protein rich sensitive product, such as meat.^[9] In microwave cooking, the process parameters, such as power and cooking time, had great influence on the quality attributes of the product.^[10]

High amount of fat used in the manufacturing of kavurma affects adversely the quality due to lipid oxidation during the production and also during the storage.^[2,11,12] Meat quality parameters such as color, flavor, odor, texture, and even the nutritional value are affected from oxidation. The main flavoring compounds are formed by this reaction.^[13] Flavor is the main sensory attribute of cooked meat products that affects the consumer preferences. There are hundreds of compounds in meat that contribute to flavor and aroma that may have been altered during cooking and storage such as hydrocarbons, aldehydes, ketones, alcohols, furans, pyrrols, pyridines, sulphur containing compounds, etc.^[14,15] Main flavoring compounds are formed by lipid oxidation, Maillard reaction, protein degradation, and oxidation of flavoring compounds.^[16–19]

Textural attributes of meat and meat products are followed during the processing and storage periods.^[20] The main texture defects during the production of kavurma come from low-quality raw material, improper cooking, cooking conditions, high water and fat content, and pH values, etc.^[2,21,22] Due to the heat treatment, it could cause the texture to be too hard and more browning could also be caused.^[21]

The Turkish Standard Institute declared that for high-quality kavurma; meat pieces must not be elastic, should be easily torn up, and be light-brown. There must be no air in the package and the fat content must be 25–30% of meat, the fat between two meat pieces must not be more than 1–2 cm² in size.^[23] Most importantly, there shouldn’t be cooking losses that have an effect on quality parameters of kavurma, such as moisture content, pH, color, 2-thiobarbituric acid reactive substances (TBARS) value, and textural properties. General specialties and quality of kavurma are determined according to the Turkish Standard Institute.^[23] The main texture defects during the production of kavurma are caused by low-quality raw material, no or incorrect cooking, high water and fat content, conditions of cooking, and pH values, etc.^[2,22] Due to the heat treatment, more browning and a harder texture could be attained in meat products.^[21]

There is not enough information in the literature with regard to the effect of different cooking techniques on quality attributes of kavurma during processing. As it is known, cooking is the preservation method which makes the meat safe to eat. It has both positive and negative effects on quality attributes of meat. The main chemical and physical changes occuring in the cooking period of kavurma production and storage period depend on the cooking periods. The microwave method was selected and used as an alternative method to be able to shorten the process time for Kavurma production. Therefore, this study was conducted to clarify the effects of different cooking on the quality attributes of kavurma. The objective of this study was to assess changes in moisture content, textural attributes (hardness and chewiness) as well as the other quality parameters; pH, TBARS value, and color attributes of kavurma during the processing by performing atmospheric, pressure, and microwave cooking techniques.

MATERIALS AND METHODS

Materials

Beef (Longissimus dorsi), sheep tail fat, and table salt were obtained from a local supermarket in Gaziantep, Turkey. 1,1,3,3- tetraethoxypropane (TEP) and 2-thiobarbituric acid were obtained from Sigma (St. Louis, MO); glacial acetic acid from Merck (Darmstadt, Germany), and perchloric acid from JT Baker (Holland). All chemicals were analytical grade (extra pure).

Kavurma Production

Kavurma was produced according to the procedure described by Aksu and Kaya.^[2] First, the beef was trimmed from fat and connective tissue and was cut into pieces of about 5 × 5 × 5 cm. Table salt (refined and ground), 2.0% of meat weight, was added into beef. Tail fat was melted before usage and about 250 g of melted tail fat was added to 1000 g of meat. The meat was precooked with about 20% of the total tail fat (about 50 g/kg of beef) and salt at about 50°C for 30 min. Meat pieces were stirred at definite time intervals for homogeneous cooking. The end of precooking time was assumed as the beginning time of the kavurma processing. Precooked beef was divided into three parts for atmospheric, pressure, and microwave cooking. Glass was used as a container for cooking.

Atmospheric cooking was carried out in an oven (Velp, Italy). Cooking was made with remaining melted tail fat (about 200 g/kg of meat) at 120 ± 2°C. The meat was cooked at this temperature for 50 min. At each ten min of cooking, sampling was done. Duplicate batches were prepared. Pressure cooking was performed in an autoclave. The samples were prepared by adding the remaining to the beef and they were placed into the autoclave. When the temperature scale showed 121°C and pressure gauge reached the 1.5 Pa, time of cooking was started. The meat was cooked at this temperature for 50 min. Beef pieces were sampled on the 10, 20, 30, 40, and 50th minute of cooking. For that purpose, meat pieces were divided into five groups for each time, and then each group was put into pressure cooking one by one. Each group was cooked for their desire cooking time. Duplicate batches were prepared.

Microwave cooking was applied on a programmable domestic microwave oven (Arçelik ARMD 580, Turkey) with maximum output of 700 W at 2450 MHz. The oven has adjustable power (wattage) and time controllers and was fitted with a turntable. A microwave oven set at a power of 70 W and a frequency of 2450 MHz for 50 min. Beef pieces were sampled on the 10, 20, 30, 40, and 50th min of cooking. Duplicate batches were prepared.

Sampling

Properties of raw meat were determined before the cooking process. Open pan and microwave cooking process samples were stirred at the 10 min time intervals at that time samples were taken. However, during pressure cooking, five separate samples were prepared for each of the time intervals. The first sample was processed at 10 min then it was separated for sampling. After that, the second was processed at 20 min, the third was processed at 30 min, the fourth was processed at 40 min, and the fifth was processed at 50 min. Therefore, stirring was not applied during pressure cooking. During the cooking, two pieces of meat from each batch were sampled on the 10, 20, 30, 40, and 50th min of cooking. In raw or cooked samples, textural attributes, hunter color values (L*, a*, and b*), moisture, TBARS, and pH were determined. Samples were left for about 5 min in the room conditions and color and textural attributes were measured immediately. For accurate statistical comparison, two batches were prepared.

Sample Preparation

Texture and color attributes were determined on a meat piece. Meat pieces were cut by a sharp knife for texture and color analysis at about 20 × 20 × 20 ± 0.5 mm dimension. Color was measured on the cut surface. The remaining samples were cut into small pieces (about 5 × 5 × 5 mm) and homogenized using a Waring blender (Torrongton, CT, USA). Twenty grams of the homogenized samples were used for the determination of moisture content, pH, and TBARS values.

Instrumental Texture Profile Analysis (TPA)

For TPA, cut meat pieces were held for equilibration to room temperature (~20°C). TPA tests were performed using a TA.XT2 Texture Analyzer (Texture Technologies Corp., Scarsdale, NY/Stable Microsystems, Godalming, UK) to determine hardness and chewiness.^[12] Test conditions were: aluminum rectangular probe (4 cm × 5 cm); test speed 1 mm/s; pre-test speed 2 mm/s, post-test speed 1 mm/s; compression (strain) 25%; and 25 kg load cell. Data collection and calculation were done using the Texture Expert Exceed Version 2V3 (Stable Micro Systems, 1998).

Determination of Hunter Color Values

Color measurement (Hunter L*, a*, and b*) were made by using a Hunter lab ColorFlex (A60-1010-615 Model calorimeter, Hunter lab, Reston, VA).^[11] The instrument was standardized at each time with a white and black ceramic plates (Lo = 93.01, a₀ = –1.11, and b₀ = 1.30). The Hunter L*, a*, and b* values correspond to lightness (L*), greenness (–a*) or redness (+a*), and blueness (–b*) or yellowness, (+b*), respectively. The color measurements were performed on the cut surface of kavurma after equilibration to room temperature (~20°C) in duplicate for each batch.

Chemical Analysis

The measurement of pH value was carried out on 10 g of sample homogenized in distilled water (1/10 sample/water).^[12] The pH value of the sample was determined using a pH meter (Jenway 3010; Jenway LTD, Essex, UK) equipped with a J95, 924001 electrode (Jenway LTD, Essex, UK). TBARS values of kavurma were determined by the spectrophotometric method.^[24] Two grams of the homogenized kavurma sample was taken and TBARS were extracted twice with 10 mL of 0.4 M perchloric acid. Extracts were collected and made up to 25 mL with 0.4 M perchloric acid and centrifuged at 1790 × g for 5 min. After centrifugation, 1 mL of supernatant was pipetted into glass stoppered test tubes. Five milliliters of TBA reagent was added and the mixture heated in a boiling water bath for 35 min. After cooling, the absorbance of sample was read against the appropriate blank at 538 nm. A standard curve was prepared using TEP. The moisture content of the samples was determined by oven methods at 105°C.^[25]

Statistical Analysis

An ANOVA was performed for texture, color attributes, pH, moisture content, and TBARS values as a function of cooking time to determine significant differences (p < 0.05) using the SPSS version 21.0 (SPSS Inc., Chicago, IL, USA). Duncan’s multiple range test was also carried out during the cooking period for determination homogeneous groups.

RESULTS AND DISCUSSION

Changes in Moisture Content Values

The moisture content of the samples obtained by three different methods during the cooking process was followed and their results are given in Fig. 1. Moisture content of raw meat was measured as 75.39%. As it is seen in this figure, at each three method, moisture content values of samples decreased regularly by the time during the processing. This could be due to more water being forced out as the meat is cooked progressively. Statistical analysis indicated that moisture content of samples by atmospheric and pressure cooked wasn’t affected significantly (p ˃ 0.05) by time, but the samples of microwave cooked were significantly affected by time after 10 min of processing. When comparing the methods at each time, changes in moisture content for samples which were processed by microwave cooking were found to be significantly different (p < 0.05) from atmospheric and pressure cooking especially at 10 and 30th min. This could be due to the fact that foods with a higher moisture content in microwave cooking will be heated up faster because of the dipolar interaction.^[8] At 50th min, the samples of microwave cooking in moisture content were lower as compared to those prepared with atmospheric and pressure cooking methods. Also, Janicki and Appledorf^[26] studied microwave cooking on ground beef and they found that patties processed with the microwave had lower moisture content than the broiling and grill frying methods.

FIGURE 1 The change in moisture content values of Kavurma samples during the production at each minute.

The moisture content values of samples were found to be in the range of 66.82–51.64% during the processing (Fig. 1). The lowest moisture content value (p < 0.05) was obtained at the end of time as 51.64% in microwave cooking. According to the Turkish Standard Institute,^[23] the moisture content should be 40% at the maximum in kavurma. Cooking time was selected according to the microwave cooking method, after the 50th min the color became too dark and it was so hard that it was not suitable for consumption. So the cooking was stopped for the comparison of these three methods. In this study, desirable moisture content values couldn’t be reached at each method at the end of 50 min cooking; this could be due to the difference between (aw) water pressure of meat during cooking and room water pressure. The decrease in moisture in the microwave cooked meat could be attributed by increasing this difference.

Changes in pH Values

Change in pH values during the cooking by three different methods are given in Table 1. In this study, the pH of beef was measured as 5.74. The mean pH of beef used in this study was in accordance with that observed by Boles and Swan.^[27] Moreover, Klont et al.^[28] stated that the highest quality meat was indicated by the pH range of 5.7 to 6.0.

TABLE 1 Statistical results for changes of pH of kavurma during the production

Processing time	Atmospheric cooking	Pressure cooking	Microwave cooking
Raw meat	5.74aX	5.74aX	5.74aX
10	5.77aX	5.82aX	6.80bY
20	5.76aX	5.70aX	7.40cY
30	5.75aX	5.74aX	7.57cY
40	5.81aX	5.80aX	7.44cY
50	5.75aX	5.80aY	7.26cZ

Different small letters indicate statistical difference between cooking time values at a = 0.05 level in each column;

Different capital letters indicate statistical difference among the methods at a = 0.05 level at each time.

According to one way ANOVA results, time generally had a significant effect (p < 0.05) on the pH value of microwave cooked samples. Along the cooking (0–50 min) of beef, at each time, the pH values of microwave cooked samples were significantly different (p < 0.05) from atmospheric and pressure cooking methods. While the pH values along 50 min processing were varied between 5.70 and 5.82 in atmospheric and pressure cooking, in microwave cooking, the pH values varied between 6.76 and 7.57. The pH values of atmospheric and pressure cooked samples also were in agreement with literature and the Turkish Standard. According to kavurma standard,^[23] the pH of kavurma should be between 4.5 and 6.4. However, microwave cooked samples already exceeded the limit. The higher pH values in microwave cooking may be attributed to fast heating rates in the microwave oven which causes higher loss of free acidic groups. Cooking at higher temperatures, free hydrogen sulphide begins to form and increases with increasing temperature.^[6]

Changes in TBARS Values

TBARS values were followed to measure the degree of the lipid oxidation (Fig. 2). According to one way ANOVA results, at each three method, TBARS values increased (p < 0.05) during the cooking process. This could be due to the face that cooking caused to breakdown of lipoprotein complex in meat and so lipid fraction could be released and become more susceptible to oxidative attacks.^[29] Tims and Watts^[30] reported that cooking increased lipid oxidation in muscle and could increase TBARS values. Cooking at high temperatures and long times improve oxidative changes in food, which could be really negative for quality.

FIGURE 2 The change in TBARS values of Kavurma samples during the production at each minute.

In this study, during the 50 min cooking process, TBARS values of kavurma samples were found to be in the range of 0.17–0.30 mg MA/kg for atmospheric cooking, 0.65–0.81 mg MA/kg for pressure cooking, and 4.26–4.52 mg MA/kg for microwave cooking. Rodriguez-Estrada et al.^[9] observed that microwave treatment (shorter time and lower temperature) caused high oxidation. Many authors explained this fact by showing a decrease of polyunsaturated fatty acid (PUFA) from phospholipids in different foods after microwave cooking, relating this result, to a likely increase of oxidation products originated from these fatty acids.^[31,32] On the other hand, results of TBARS value for atmospheric cooking were in agreement with the previous studies. Yetim et al.^[22] found that TBARS values of kavurma samples were in the range of 0.125–2.56 mg MA/kg. İbik et al.^[33] analyzed the TBARS values in beef kavurma and they found 0.2 mg MA/kg. Domínguez et al.^[34] studied the influence of four different cooking methods (roasting, grilling, microwaving baking, and frying with olive oil) on some chemical and physical attributes of foal meat was studied. They found that cooking losses were higher (29.9%) after microwaving and lower after grilling (19.1%) treatments and roasted or microwaved had higher TBARS content.

Wu et al.^[35] reported that if the TBARS value is higher than 1 mg MA/kg generally off-odors are formed and it is considered as the beginning of organoleptic perception of lipid oxidation. By the lightening of this result, atmospheric and pressure cooked kavurma samples couldn’t be considered as rancid since the TBARS values were lower than that of threshold value of 1 mg MA/kg. On the other hand, since microwave cooking induced significantly higher lipid oxidation, microwaved cooked samples could be considered as rancid.

Changes in Hunter Color Values

The color of cooked meat product is an important parameter for the consumer preferences and also for the shelf life. Changes in Hunter color values were measured during cooking process (Table 2). The lightness values of whole samples during kavurma production were in the range of 35.51–51.50 as shown in the Table 2. This finding is in agreement with the results of some researchers. In the literature, Arvanitoyannis et al.^[1] found the mean lightness value as 45.6 in kavurma samples. Aksu and Kaya^[2] reported that lightness parameter in their control kavurma sample reached to 44.4. İbik et al.^[33] also found that the lightness in beef kavurma was 43.1. Inserra et al.^[36] studied the effect of replacing cereal concentrates with high levels of dried citrus pulp in the diet on lamb meat oxidative stability. They found that control diet increased the redness, yellowness, and saturation of meat and dietary dried citrus pulp strongly reduced meat lipid oxidation over six days of aerobic storage.

TABLE 2 Statistical results for changes of Hunter color values of kavurma during the production; lightness values (L*)

Processing time (min)	Atmospheric cooking	Pressure cooking	Microwave cooking
Raw meat	39.82aX	39.82abX	39.82aX
10	48.45bX	46.55cX	47.10cX
20	48.78bX	45.28cY	48.09cX
30	49.18bX	41.47bY	47.50cX
40	50.89cX	39.51abY	44.34bZ
50	51.50cX	37.92aY	40.34aY
Redness values (a*)
Raw meat	16.08aX	16.08aX	16.08aX
10	9.18bX	6.90cY	6.01bZ
20	5.82cY	7.13cY	4.75cZ
30	5.83cX	7.95bcY	5.19cX
40	5.85cX	8.59bY	6.23bX
50	5.53cX	8.84bY	6.71bZ
Yellowness values (b*)
Raw meat	15.47aX	15.47aX	15.47aX
10	15.34aX	16.91aY	14.86aX
20	13.97bX	19.48bY	14.38abX
30	13.77bX	20.12bY	13.27bcX
40	13.48bX	20.65bY	13.66bcX
50	13.94bX	21.48bY	12.97cX

Different small letters indicate statistical difference between cooking time values at a = 0.05 level in each column;

Different capital letters indicate statistical difference among the methods at a = 0.05 level at each time.

The results of statistical analysis showed that lightness (Hunter L*) values were affected significantly (p < 0.05) by cooking time. L* values of the atmospheric cooked sample increased (p < 0.05), but for pressure and microwave cooked samples lightness value decreased by time. Decrease in lightness value illustrates decreasing of the lightness and formation of dark color due to the browning reaction.^[37] The increasing of lightness value could be due to evaporation of moisture. From this point, it could be understood that 50 min was not enough for atmospheric cooking to have desirable brown color of kavurma.

During the cooking, Hunter a* (redness) values decreased in atmospheric cooked samples. By using a longer cooking time, a reddish reduction (deoxymyoglobin and oxymyglobin denaturation) and an increase in brownish-red and greenish (metmyglobin and sulfmyglobin species) could be obtained so this caused to decrease of a* values. Pressure and microwave cooked samples, display a more intense reddish color and a* values were significantly higher (p < 0.05) than atmospheric cooked samples. It may be associated with the myoglobin degradation that could be lower in these techniques. The similar trend was observed for yellowness (Hunter b*) values as it was in redness values. Cooking time caused to decrease in yellowness value for atmospheric cooked samples. Similar results were also observed by Kayaardı et al.^[38] who found that Hunter b* values of kavurma decreased during the storage periods.

Changes in Instrumental Textural Attribute (TPA)

Texture profile of kavurma (hardness, chewiness) was followed during the 50 min processing by three different methods and results are shown in Table 3. Ruiz de Huidobro et al.^[39] observed that there is a strong correlation exists between the TPA (hardness and chewiness) and sensory attributes in both raw and cooked meat. Hardness and chewiness values increased significantly (p < 0.05) during the cooking process for both atmospheric and microwave cooked samples. In microwave cooking, the hardening of meat could be due to its lower moisture content. However, for the samples of pressure cooking, time did not have a significant effect (p ˃ 0.05) on hardness and chewiness (Table 3). This could be raised from the differences in these techniques for kavurma production. In atmospheric and microwave cooking technique, the protein begins to coagulate to the point where it starts to squeeze out moisture, release much of its juice and the meat starts to consequently shrink, dry out, and get tough. However, in pressure cooking, there is steam that is produced by the boiling of liquid inside the meat. There was no way of loss of water; therefore, moisture content became constant in this method. Zell et al.^[40] studied different preparation techniques before ohmic cooking of beef muscle (biceps femoris) at pasteurization temperatures. They found that ohmically heated meat had a significantly uniform lighter and less red color, lower cook loss, and tougher than the conventionally cooked products.

TABLE 3 Statistical results for changes of textural attributes of kavurma during the production; hardness values (N)

Processing time (min)	Atmospheric cooking	Pressure cooking	Microwave cooking
Raw meat	3.29aX	3.29aX	3.29aX
10	4.86aX	8.24aX	4.74aX
20	7.01abX	8.25aX	9.92abX
30	7.57bX	8.52aX	26.50cY
40	8.12bX	9.03aX	17.80bcX
50	13.20cX	9.15aX	15.55aX
Chewiness values
Raw meat	1.84aX	1.84aX	1.84aX
10	2.68aX	2.97aX	4.88aX
20	4.11abX	3.58aX	7.22aX
30	4.32bX	3.61aX	18.41bY
40	4.63bX	3.78aX	13.37abX
50	8.14cX	4.40aXY	12.83aX

Different small letters indicate statistical difference between cooking time values at a = 0.05 level in each column;

Different capital letters indicate statistical difference among the methods at a = 0.05 level at each time.

Statistical analyses indicated that there were not significant differences (p ˃ 0.05) on hardness and chewiness value between the methods at each time except the sample of microwave cooking at 30th min. At this time, the hardness and chewiness value increased to 26.50 N and 18.41 N, respectively, and dry crust formation occurred on the surface of it. This is not desirable because the hardness value of kavurma shouldn’t be so high. Rababah et al.^[41] found that chicken breast meats cooked by the microwave method had higher hardness and chewiness values than meats cooked by the conventional electric oven. Hardness value decreased up to the end of microwave cooking. This could be due to decomposition of collagen into soft gelatin.

CONCLUSION

By way of conclusion, the results obtained in this study pointed out that cooking had numerous effects on many quality attributes and physical properties of kavurma. In this sense, the cooking time and cooking method had a great importance in the production of kavurma. In this study, the desirable quality attributes were developed better in the technique of atmospheric and pressure cooking than microwave cooking technique. The use of microwave cooking technique provided a faster heating rate; however, the important quality parameters as moisture content, pH, TBARS, hardness, and chewiness values were in desirable range at atmospheric and pressure cooking method.

ORCID

Anıl Uzun Özcan

http://orcid.org/0000-0003-4039-9389

Hüseyin Bozkurt

http://orcid.org/0000-0003-4676-6354

ACKNOWLEDGMENT

The authors wish to thank the Scientific Research Projects Executive Council of University of Gaziantep.