EFFECT OF COOKING METHODS ON AMINO ACIDS COMPOSITION OF CHICKEN MEAT ВЛИЯНИЕ СПОСОБОВ ПРИГОТОВЛЕНИЯ НА АМИНОКИСЛОТНЫЙ СОСТАВ МЯСА ПТИЦЫ

Chicken meat is an important item in the Syrian diet. The increasing production of chickens and their potential in restaurants and food service operation implies the need for more detailed information regarding their quality and nutrient retention. Cooking methods have different effects on the values of nutrients of chicken. Therefore, this study was carried out to evaluate the effect of microwave cooking in amino acids composition of chicken meat (breast &thigh) as compared with some conventional methods, i.e. boiling, pressure and roasting. Аннотация Мясо птицы является важной составляющей сирийской диеты. Увеличение производства мяса птицы, его широкое использование в заведениях общественного питания диктует необходимость наличия подробной информации о качестве и  содержании питательных веществ в  нем. Установлено, что кулинарные методы обработки по-разному воздействуют на наличие питательных веществ в  мясе птицы. Таким образом, данное исследование проводилось с  целью оценить воздействие приготовления в микроволновой печи на состав аминокислот мяса (филе и бедро) цыплят-бройлеров по сравнению с традиционными методами кулинарной обработки: отвариванием, приготовлением под давлением и поджариванием. УДК/UDC: 637.5 ́65.04/07:641.5 DOI 10.21323/2414-438X-2016-1-4-11-18


Introduction
In Syria chicken occupies a major place in production and consumption among poultry.It has become the second most popular meat eaten and is most likely to maintain this position.Chicken meat is a good source of protein and many nutrients, and is relatively low in fat, especially if the skin is removed.Chicken meat is also characterized by versatility in menu planning, ease of preparation, consistent quality, and the availability of wide range of pre-packaged, branded, raw and ready to eat and serve products.
In many countries microwave cooking and processing have increased over the years because of its convenience and time saving.Improvements in the design of high-powered microwave ovens offer rapid and economic methods for manufacturing food products of high organoleptic properties and nutritional value [13].
In the food industry microwaves are used for pasteurization of packaged products, for sterilization, tempering of frozen foods, precooking of poultry products and snack food also.Microwave use becomes of great importance because of its extensive utilization at home for cooking, thawing and re-heating.It is used also in research due for nutrient retention in processed food [11].
Happich et al. [7] reported that the quantity of nonessential amino acids varies, and that this variation is largely accounted for by the difference in glycine, hydroxylsine and hydroxyproline.Total non-essential amino acids supply nitrogen for the synthesis in the body of any of the nonessential amino acids, which may be lacking.Besides, Barr et al. [5] and Hamm [6] reported that amounts of valine, leucine, isoleucine and histidine were great in breast meat, whereas, thigh meat had more glycine, hydroxyproline, hydroxylysine, threonine and serine.
Furthermore, results indicated that area of production and related management practices appeared to influence the concentration of about half of the amino acids.Moreover, meat from males contained more hydroxyporline than that from females.
In addition, Hamm [6] analyzed broiler breast and thigh meat samples from birds grown and processed in four locations of the U.S. for their amino acid composition.On percent protein basis amounts of valine, leucine, isoleucine and histidine were significantly greater in breast and glycine, hydroxyproline, hydroxylysine, threonine and serine were greater in thigh meats.Meanwhile, Moawad, [12] reported that the total amino acids, total essential amino acids and non-essential amino acids for fresh cooked beef meat were found to be 86,34, 33,01 and 53,33g/16g N respectively.
Therefore, the aim of this research was to study the effect of different cooking methods (boiling, pressure-cooking, roasting and microwave) on amino acids composition of chicken meat (thighs and breasts).

Materials and methods
The broilers used in this study were obtained from the local Damascus markets.Their weight ranged between (1100-1400 g) and the average age 8 weeks.
Chickens were slaughtered, plucked by hand, cleaned and washed with water.The wings, neck and heads were removed by hand.The carcasses were then cut into four parts (two breast pieces and two thighs).Chicken parts (thighs and breasts) were cooked by the following methods: 1 -Boiling: Chicken parts (thighs and breasts) were cooked in sufficient amounts of boiling water to cover it at ratio 2:1 (water: chicken) for 30 minutes. 2 -Pressure-cooking: Chicken parts (thighs and breasts) were placed in a pressure cooker and cooked for 20 minutes.3 -Roasting: Chicken parts (thighs and breasts) were roasted by using a preheated conventional electric oven to 180 °C for minutes.4 -Cooking by microwave oven: Two thighs and two breasts were placed in a baking dish and cooked in Microwave oven on a high power level for 20 minutes, 10 minutes on one side and 10 minutes on the other.Moisture, ash, total lipids and total protein were determined according to the methods recommended by the A.O.A.C. [4].All determination was performed in triplicates and the mean values were reported.
Samples were weighed (20-30 mg) in the ampoules and 5 mls. of 6 N HCl were added.The ampoules were then sealed under vacuum.Samples were then heated in an oven at 110 °C for 24 hours.The sealed ampoules were then opened and the hydrochloric acid was evaporated under vacuum.Sodium citrate buffer (pH 2,2) was used to dissolve the samples and to dilute it to the required volume.The filtrated hydrolysate was used for the amino acid analysis in High Performance Amino Acid Analyzer (a sample of 50 µL-volume was injected).
Numbers presented in the tables are the mean values of three concurrent iterations.Statistical analysis was based on the one-way analysis of variance; homogeneous groups were formed according to the Duncan test for P < 0,05.The data were statistically analysed using STATISTICA (data analysis software system).

Results and discussion
Fresh raw chicken breast and thigh meat samples were analyzed for their moisture, protein, fat, and ash.The obtained results are, hereafter shown in Table 1.
The analysis data in Table 1 indicated that the moisture content of chicken breast samples was approximately 1,0 % higher than thigh meat samples.The percentages of moisture of fresh raw breast and thigh meat were 74,15 and 73,07 %, respectively.
As expected, the percentage of fat in chicken breast meat was significantly lower than that in thigh meat (P < 0,05).Average fat contents of fresh raw chicken breast and thigh meat were 12,18 and 21,65 % (on dry weight basis), respectively.
The effect of cooking treatments on amino acids content of chicken meat is shown in Table 3. From the results in the table, it is clear that cooking of either fresh breast or thigh meat samples caused some decrease in all of their amino acids.The chicken breast and thigh meat samples cooked by pressure retained the highest percentages of total essential, non-essential and total amino acids, followed in a decreasing order by boiling, microwave and roasting methods (P < 0,05).However, no significant differences were found among cooking methods on amino acids content (P > 0,05) in either chicken breast or thigh meat samples.As a result of cooking of fresh breast and thigh meat samples by pressure, the total amino acids were found to decrease from 88,95 to 84,21 and from 87,11 to 81,16 g/16g N, respectively.Meanwhile, they decreased from 88,95 to 81,43 and from 87,11 to 77,43 g/16gN, in the fresh breast and thigh meat samples cooked by roasting respectively.Marked amounts of sulpher containing amino acids, i.e. leucine, tyrosine, phenylalanine and lysine (as essential amino acids) as well as serine, glycine, alanine, histidine and arginine (as non-essential amino acids) were destroyed, while as slight decrease was noticed in all the other amino acid contents under cooking of chicken breast or thigh meat samples.
Furthermore, from the same obtained results it was clear that cooking of either fresh breast or thigh meat samples caused some decrease in all their amino acids.The reduction of amino acid content might be attributed to their loss with drippings separated during cooking as well as by the heat destruction.