Comparative Study of Different Cooking Methods on Nutritional Attributes and Fatty Acid Profile of Chicken Meat.
Summary: The effects of different cooking methods (boiling, grilling, frying and microwave roasting) on the nutritional quality of chicken meat were assessed by measuring quality parameters i.e. moisture, ash, protein, fat and fiber contents. The fatty acid composition of chicken fat was analyzed by GC-FID. The chicken fat was found to contain high levels of oleic acid (38.0-47.3%) followed by linolenic acid (13.3-28.0%) and palmitic acid (2.0-13.6%). Different cooking methods exhibited significant effect (p [?] 0.05) on the fatty acid composition and other nutritional parameters of meat samples. Generally, fried meat had lower saturated fatty acid contents. It can be concluded from this study that boiling and frying are healthy cooking practices while grilling and microwave roasting show some negative effects.
Keywords: Frying, Fatty acid composition, microwave roasting, protein contents.
Meat seems to be a major source of fat in diet, especially of saturated fatty acids [1, 2]. It is an important as a carrier for the fat-soluble vitamins such as vitamin A, D, E and K. Meat and meat derivatives are also excellent sources of all the B- complex vitamins such as pantothenic acid, folacin, niacin, biotin, thiamin, riboflavin, vitamins B6 and B12. Pantothenic acid and folacin are especially abundant in liver which, together with some other organs is rich in vitamin A and supplies considerable amounts of vitamins D, E and K . Nowadays, there is a strong concern among meat consumers over nutritional diseases of wealth and correlation between food habits and health.
Cooking is necessary to develop desirable flavours in meat as well as to destroy harmful organisms. But the oxidation of fats results in the production of the compounds that decompose to aldehydes, alcohols, esters and short chain carboxylic acids with undesirable effect [3-5]. One of the main comparisons between raw and low-temperature cooking is that heating above 104degF (40degC) results in progressive damage of enzymes. It is reported that qualitative changes in food during cooking are more pronounced at high temperature and longer cooking time [6, 3, 7]. Meat is particularly susceptible to heating because of the presence of unsaturated lipids which are rapidly oxidised because of the catalysis by haeme and non-haeme iron . Lipid oxidation products are related to atherosclerosis, Alzheimer's disease, cancer, inflammation or aging processes [8,9].
Meat is a necessary component of Muslims foods. According to a report in 2003, an average Pakistani consumed three times more meat than an average Indian. Therefore, the main purpose of this study was to evaluate the affect of cooking methods on the nutritional values of chicken meat. Moreover, the fatty acid composition of fat from the cooked meats was also studied by GC-FID.
Results and Discussion
Nutritional Value of Chicken Samples Cooked by Different Methods
Moisture contents of raw and cooked meat samples by different methods are presented in Table-1. The cooking treatments reduced the moisture content. The total moisture contents were found in the range of 54.52-74.42% of the samples. The maximum moisture content (74.42 %) was found in uncooked sample and that of minimum (54.52 %) in microwave roasted sample. Moisture contents of roasted and raw chicken samples were comparable to data reported previously .
Table-1: Effect of different cooking methods on physico[?]chemical composition of chicken meat
Moisture (%)###74.42 +- 1.70d###65.20 +- 2.47b###63.79 +- 2.26b###69.52 +-1.81c###54.52+- 1.33a
Ash (%)###1.7 +- 0.15a###3.1 +- 0.25b###1.8 +- 0.12a###3.7 +- 0.26b###3.3 +- 0.29b
Crude protein (%)###19.57 +- 0.78b###13.94 +- 0.84a###18.31 +- 0.73b###18.83 +-0.75b###13.93 +-0.70a
Fat (%)###3.07 +- 0.96b###3.80 +- 0.27c###7.96 +- 0.64d###9.09 +-0.82e###2.31 +-0.21a
Crude fiber (%)###0.12 +- 0.01a###0.16 +- 0.01c###0.15 +- 0.01b###0.61 +-0.04e###0.33 +-0.03d
Ash contents of raw and cooked meat samples are shown in Table-1. Results showed that all cooking treatments increased the ash contents of meat samples. The total ash contents ranged from 1.7-3.7%. Highest ash content was obtained from fried meat sample whereas lowest from raw one. The value of ash contents of all chicken meat samples obtained from the present analysis was higher than that for buffalo meat reported previously .
The protein contents of all meat samples are given in Table-1. Results indicated that all cooking treatments decreased the protein contents. The protein contents of all chicken meat samples were ranged from 13.93 to 19.57%. Raw meat showed highest protein content (19.57%). Whereas, grilled and microwave roasted samples showed least protein contents among all samples i.e. 13.94 and 13.93%, respectively. Protein contents are good parameter for assessing the quality of meat and meat products. The results of our present investigation were in good agreements with the findings of Nobrega et al. and Olvera-novoa et al. working in the same area [11, 12]. However, our findings are contradicting with the findings of some researchers  who reported increase in protein contents of buffalo meat after cooking. This variation might be due to different meat textures.
The fat contents of chicken meat samples are also presented in Table-1. The fat contents of all samples varied significantly (p [?] 0.05). Fat contents of all meat samples ranged from 2.31 to 9.09%. All coking treatments caused an increase in fat content except microwave cooking. The fat contents of tested chicken meat samples was higher than reported previously [10, 13] who investigated the higher fat contents in pig meat than chicken meat samples.
Results showed a significant (p [?] 0.05) increase in fiber contents after all cooking treatments as compare to uncooked meat sample (Table-1). Present analysis showed that cooking of meat caused an increase in fiber contents. In present analysis the fiber contents of raw chicken samples was higher than reported previously . This variation in fiber content might be attributed to species variation.
Fatty Acid Composition
The fatty acid composition of each chicken meat sample is presented in Table-2 (Fig. 1-4). Palmitic acid (C16:0) and stearic acid (C18:0) were the major saturated fatty acids while palmitoleic acid (C16:1) and oleic acid (C18:1) were the main monounsaturated fatty acids; and linoleic acid (C16:2) was the dominant polyunsaturated fatty acid in the all meat samples. Data showed that cooking treatments caused a significant increase (p [?] 0.05) in myristic acid (C14:0) and stearic acid (C18:0) contents. There was an unusual difference in palmitic acid (C16:0) content among all cooking treatments. Grilling, boiling and microwave roasting showed higher palmitic acid content than uncooked meat whereas frying caused a decrease in palmitic acid (C16:0) content. Palmitoleic acid (C16:1) content was significantly increased by boiling and microwave roasting whereas decreased by grilling and frying.
In the case of stearic acid (C18:0) grilling, boiling and microwave roasting causd a significant increase but frying caused a decrease in percentage stearic acid content. Oleic acid (C18:1) exhibited highest percentage among all observed fatty acids. This fatty acid showed a difference than other fatty acids in the way that it was decreased by all cooking treatments. On the other hand different cooking treatments caused different effects on other fatty acids. Oleic acid (C18:1) was the more abundant fatty acid detected followed by linoleic acid (C18:2). Frying showed similar effect on linoleic acid as on myristric acid (C14:0). Grilling caused a small increase whereas boiling and microwave roasting caused a decrease in linoleic acid content. Behenic acid (C22:0) was only detected from grilled and fried chicken samples. Behenic acid (C22:0) content was high (9.5 %) in fried sample as compare to gilled sample (5.2 %).
The percentage composition of saturated fatty acids (SFAs) was 18.5, 29.4, 30.2, 25.8 and 30.0% from raw, grilled, boiled, fried and microwave roasted samples, respectively. Microwave roasting showed highest concentration of (SFAs). The percentage
composition of monounsaturated fatty acids (MUFAs) was 56.4, 46.1, 48.5, 45.6 and 55.1% in raw, grilled, boiled, and fried and microwave roasted samples, respectively. Raw meat exhibited highest whereas fried meat exhibited lowest (MUFAs). The
concentration of monounsaturated fatty acids was higher in all chicken samples as compare to saturated fatty acids and polyunsaturated fatty acid.
Myristric acid (C14:0) and palmitic acid (C16:0) are main saturated fatty acids that have been reported to be responsible to raise the level of total and low-density lipoprotein (LDL) cholesterol [15-17]. No such study has been published with which the results of present investigation can be compared. However, some reports in literature available on the fatty acid composition of meat samples [3, 15, 18-20]. The average value of each of the fatty acids composition in the meat samples with other published data vary because of the numerous factors which can affect fatty composition of each meat, i.e. geographical location, age, sex, diet, physiological acclimatization, part of carcass used, etc [18-21].
Chemicals and Reagents
All the chemicals and reagents (analytical grade) used were purchased from E. Merck (Darmstadt, Germany) or Sigma Aldrich (Buchs, Switzerland), unless stated otherwise.
Samples Collection and Pretreatments
The fresh chicken meat (broiler) was purchased from local market of Faisalabad, Pakistan. The chicken was washed with tap water after removing manually inedible part and bones with a sharp steel knife, cut into almost equal small pieces, and then mixed well. The processed samples were divided into five parts (200 g each) and subjected to different cooking processes (boiling, grilling/BBQ, frying and microwave roasting), keeping one portion as control (uncooked).
Boiling: 200 g of chicken sample was added to 300 mL of water that had just reached to boiling in a stainless steel pan and boiled for 5 min. After boiling the chicken, the excessive water was drained off.
Grilling/BBQ: For the grilling, charcoal was placed in the bottom of an oven, and start to fire for 5 min. When all flame had subsided, the charcoal was leveled by raking. 200g of chicken sample was put on iron rods and then grilled over charcoal for 5 min per side, total cooking time was 10 min, the distance between samples and charcoal was about 8 cm. The surface temperature of the samples was measured about 200degC.
Frying: Two tablespoons of season sunflower oil was heated in a stainless steel pan and sample (200g) was fried for 5 min. The sample was cooled under fan and washed thrice with hexane to remove oil. Samples were subjected to air-drying under fan to evaporate any traces of hexane.
Microwave Roasting: 200g of chicken sample was placed in a glass dish. The dish was covered with aluminum foil having several holes and cooked by using domestic microwave oven at a frequency of 2450 MHz (medium power setting, capable of generating 500 W). Cooking took 5 min.
Evaluation of Nutritional Value of Chicken Samples Cooked by Different Methods
Moisture content was determined following the standard method of association of Official Analytical Chemists . In brief, 5g of each sample was taken in Petri dishes and dried in hot air oven at 70degC for 24 hours, till constant weight. The moisture contents were calculated by the formula given below:
Ash content was determined following the standard method  method. Two grams of the test portion was taken and carbonized by heating on a gas flame in a pre-weighed crucible. The carbonized material was then ashed in an electric muffle furnace (TMF-2100, Eyela, Tokyo, Japan) at 600oC till white ash achieved.
Crude Protein Contents
Protein content (N x 6.25) was determined following the standard method . The Nitrogen contents of each sample were determined by using the Kjeldahl's method. For protein estimation the Nitrogen contents were multiplied by 6.25 (conversion Factor). To determine Nitrogen contents in the given samples, duplicate sets of 2g of dried chicken sample was added to digestion mixture (Copper sulphate, Ferric sulphate and Potassium sulphate in the ratio of 1:9:90) then added 10 mL of concentrated H2SO4. Then digested this mixture using anti-bombs for one hour on the water bath till the solution became clear and then diluted with distilled water to make the volume of the solution up to 50 mL. Then took 10 mL from the above solution and added 10 mL of 40 % NaOH and 10 mL of distilled water and transferred to distillation chamber. 10 mL of 2 % boric acid and few drops of methyl red as an indicator were used to receive the Ammonia at receiver end.
Ammonia gas librated combined with water and converted into ammonium hydroxide. Then it was received in the receiver. Ammonia gas was absorbed in the form of Amborate (pink to yellow). Distillate was titrated with 0.1N H2SO4. When the color of distillate was changed from yellow to pink during neutralization the volume of acid was noted and then made calculation by using the formula given below.
Then calculated the crude protein (% age) by the formula given below;
Crude protein % age = N % age x 6.25
Crude Fat Contents
All the chicken samples were crushed and then that crushed material was used for extraction purposes. Each ground chicken sample (100 g) was fed to a Soxhlet extractor fitted with a 0.5 L round- bottom flask and a condenser. The extraction was executed on a water bath for 6 h with 0.3 L of n-
hexane. The solvent was distilled off under vacuum in a rotary evaporator (Eyela, N-N Series, Rikakikai Co. Ltd. Tokyo, Japan) at 45oC.
Weighed the amount of fat extracted from each sample and calculated the yield of fat for each sample individually. The extracted fat was stored under refrigerator (4oC), until used for further analyses.
Crude Fiber Contents
Fiber content was estimated following the standard method . Each finely ground sample (2g) of chicken was weighed and freed from fat by extraction with 15 mL n-hexane. The test portion was boiled with 250 mL of sulphuric acid (0.12N) for half an hour, followed by separation and washing of the insoluble residue. The residue was then boiled with 250 mL of sodium hydroxide (0.313N) for half an hour, followed by separation, washing, and drying. The dried residue was weighed and ashed in a muffle furnace (TMF-2100, Eyela, Tokyo, Japan) at 600oC, and the loss of mass determined as: Wt. loss on ignition = Wt. of residue - Wt. of ash
Fatty Acid (FA) Composition
Preparation of Fatty Acid Methyl Ester (FAME)
Fatty acid methyl esters (FAMEs) were prepared following standard method . Briefly 30 mg of oil was taken in tube with a thread top and 5 mL of 0.5M potassium methoxide (prepared from a concentrated solution using methanol to dilute to the required volume) was added to each sample. The contents of the tubes were mixed thoroughly using a vortex mixer. The samples were put in a heating block for 1hour at 50oC. The samples were Vortex every 3-5 min for the first 15 min, until a monophasic system (transparent) is achieved. The sample were cooled down to room temperature and added 0.3 mL of glacial acetic acid, 3 mL iso-octane (or n-heptane) and 3 mL of distilled water into each sample. After gently mixing the samples were centrifuged at 2500 rpm for 2 min. Transferred at least 1.5 mL of the clear upper layer of the sample into labelled chromatographic vials (GC) using a Pasteur pipette.
Gas Chromatography (GC-FID) Analysis
Fatty acid methyl esters (FAMEs) prepared following standard method  were analyzed on a
Shimadzu (Kyoto, Japan) gas chromatograph, model 17-A, fitted rate, 5degC min-1; final temperature, 210degC; injector temperature, 220degC; detector temperature, 230degC; and temperature hold, 2 min before and 10 min after the run. A sample volume of 1.5 uL was injected using split mode (split ratio 1:75). FAME's were identified by comparing their relative and absolute retention times to with a methyl-lignocerate- coated film (thickness 0.20 um) SP-2340 polar capillary column (30 m x 0.32 mm; Supelco Inc., Supelco Park Bellefonte, PA), and a flame ionization detector (FID). Oxygen-free nitrogen was used as a carrier gas at a flow rate of 3.0 mL min-1. Other conditions were as follows: initial oven temperature, 180degC; ramp those of authentic standards. A data- handling program, Chromatography Station for Windows (CSW32; Data APEX LTD. CZ-15800 Pague 5, The Czech Republic), was used for quantification. The FA composition was reported as percentages.
Values are reported as mean +- SD of five chicken samples, analyzed individually in triplicate. One way ANOVA was used to determine significant differences between groups, considering a level of significance of less than 5% (P [?] 0.05) using the statistical software STATISTICA 5.5 (Stat Soft Inc, Tulsa, Oklahoma, USA).
It can be concluded from the present investigations that the cooking methods exhibit significant effect on the nutritional attributes and fatty acid compositions of chicken meat. Boiling and frying are healthy cooking practices whereas grilling and microwave roasting showed negative effects on the protein and fat contents of chicken meat. Microwave cooking was found to be responsible for the loss of essential fatty acid i.e. linoleic acid to a significant extent.
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|Author:||Hussain, Abdullah Ijaz; Chatha, Shahzad Ali Shahid; Iqbal, Tabassum; Arshad, Muhammad Umair; Zahoor,|
|Publication:||Journal of the Chemical Society of Pakistan|
|Date:||Jun 30, 2013|
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