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УДК 664
НЕЖНОСТЬ И ДЕФЕКТ МЯСА ПТИЦЫ: ОСНОВНЫЕ ПРОБЛЕМЫ СОВРЕМЕННОГО ПТИЦЕВОДСТВА
ДЖУЗЕППЕ МАЙОРАНО, профессор, Университет Молизе
(86100 Кампобассо, Италия, Университет Молизе, Департамент сельского хозяйства, окружающей среды и пищевых наук; e-mail: maior@unimol.it)
Ключевые слова: нежность, дефект, птица, мясо, птицеводство.
Потребление куриного мяса растет во всем мире главным образом потому, что оно является недорогим по сравнению с мясом других видов, и его пищевые характеристики подходят для здоровья человека. Качество мяса в целом и качество мяса птицы в частности является чрезвычайно сложным понятием, которое может быть оценено с различных точек зрения (пищевая ценность, срок годности, безопасность, содержание питательных веществ и т. д.). Качество и состав мяса птицы находятся под влиянием множества факторов, таких как генотип, пол, возраст, рацион, условия содержания и предубойной обработки птиц, пробиотиков, поставляемых в корм, или пробиотиков, содержащихся в яйце. Основным показателем качества мяса птицы является категория тушки, которая определяет его пищевой статус, принимая во внимание степень жира и мышечной ткани. Хотя есть ряд характеристик, которые определяют общее качество мяса, качество мяса птицы определяется в основном двумя чрезвычайно важными чертами: внешний вид и нежность мяса. Внешний вид (например, цвет кожи и мяса, наличие мышечных белых страт) имеет решающее значение для первоначального отбора продукта и окончательного уровня продукции. Случается, что мясо птицы не соответствует ожидаемому цвету, и это создает некоторые специфические проблемы для птицеводства. Кроме того, цвет мяса птицы может измениться, в то время как оно хранится для реализации в розницу и в домашних условиях. Если хранение осуществляется в холодильнике или морозильной камере, то изменения цвета остаются в пределах нормы для свежего мяса птицы. Нежность мяса зависит от наличия нескольких факторов, таких как сопротивление волокон, длина сар-комера, рН и морфологии коллагена экологического стресса (высокие или низкие температуры) перед убоем, борьбы до или во время убоя, метода оглушения (электрическое оглушение и вакуумное оглушение) и посмертного старения.
Инженерия /^7
TENDERNESS AND DEFECT IN POULTRY MEAT:
THE MAIN ISSUES IN THE MODERN POULTRY INDUSTRY
GIUSEPPE MAIORANO, professor, University of Molise
(Department of Agricultural, Environmental and Food Sciences, University of Molise, Via F. De Sanctis snc, 86100 Campobasso, Italy; e-mail: maior@unimol.it)
Keywords: tenderness, defect, poultry, meat, poultry industry.
The consumption of chicken meat is growing worldwide, mainly because it is inexpensive compared to the meat from other species and its nutritional attributes are suitable for human health. The quality of meat in general and hence poultry meat is an extremely complex notion that can be assessed from different points of view (eating quality, shelf life, safety, nutrient content, etc.). The quality and composition of poultry meat are influenced by numerous factors such as genotype, sex, age, diet, rearing conditions and pre-slaughter treatment of birds, and probiotics supplied in feed or pre- and probiotics in ovo. The main indicator of the quality of poultry meat is the category of a carcass, which is determined by its nutritional status, taking into account the degree of fat and muscle tissue. Although there are a number of characteristics that determine the overall quality of meat, poultry meat quality is determined mainly by 2 extremely important traits: appearance and meat tenderness. Appearance (e. g., color of skin and meat, presence of muscular white striations) is critical for both consumers' initial selection of the product and final product satisfaction. There are times when poultry meat does not have the expected color, and this has created some special problems for the poultry industry. In addition, the color of meat and poultry can change as it is being stored at retail and in the home. When safely stored in the refrigerator or freezer, color changes are normal for fresh meat and poultry. Meat tenderness sensation is affected by the presence of several factors, such as fiber resistance, sarcomere length, pH, and collagen morphology environmental stress (hot or cold temperatures) before slaughter, struggle before or during slaughter, stunning method (electrical stunning and vacuum stunning) and post-mortem aging.
Положительная рецензия представлена Е. В. Шацких, доктором биологических наук, профессором, заведующим кафедрой Уральского государственного аграрного университета.
Инженерия
The consumption of chicken meat is growing worldwide (USDA, 2012), mainly because it is inexpensive compared to the meat from other species (e. g. beef, pork, lamb) and its nutritional attributes are suitable for human health. The quality of meat in general and hence poultry meat is an extremely complex notion that can be assessed from different points of view (eating quality, shelf life, safety, nutrient content, etc.). The quality and composition of poultry meat are influenced by numerous factors such as genotype, sex, age, diet, rearing conditions and pre-slaughter treatment of birds, and probiotics supplied in feed or pre- and probiotics in ovo. The main indicator of the quality of poultry meat is the category of a carcass, which is determined by its nutritional status, taking into account the degree of fat and muscle tissue.
Composition and nutritional aspects. The structure consists of a carcass muscle, fat, bone and connective tissue, as well as cartilage and ligaments. The less bone and cartilage and more muscle and adipose tissue in the carcass determine the higher categorical and nutritional value of meat. Content of muscle tissue of the carcass varies between 40-70 %. In the case of broiler crosses muscle tissue proportion in the pectoral muscle is from 94 to 98 % and in the leg from 92 to 97 %. The most valuable is the ratio of carcass flesh and bones 4-4.5 : 1. The muscle is approximately 75 % water (although different cuts may have more or less water) and 20-25 % protein with the remaining 5 % representing a combination of fat (1.2-2.5 %), carbohydrate and minerals. The nutrient composition of chicken is a response to the diet it consumes particularly in the early stages of life. As a broiler chicken grows the composition of its carcass changes and fat deposits increase. The intramuscular fat also plays an important role in the quality (flavor and juiciness) of chicken meat.
Regarding nutritional aspects, poultry meat well fit the current consumer demand for a low-fat meat with a high unsaturation degree of fatty acids and low sodium and cholesterol levels. Regarding the fat composition, based on a single value for a 100 g lean fillet serve, lean chicken breast has relatively higher proportions of monounsaturated fatty acids (> 20 % compared to beef and tuna), and polyunsaturated fatty acids (> 30 % compared to beef, lamb and pork).
Color and tenderness. Although there are a number of characteristics that determine the overall quality of meat, poultry meat quality is determined mainly by 2 extremely important traits: appearance and meat tenderness. Appearance (e. g., color of skin and meat, presence of muscular white striations) is critical for both consumers' initial selection of the product and final product satisfaction. Poultry is unique because it is sold with and without its skin. In addition, it is the only species known to have muscles that are dramatic extremes in color, white and dark meat. Breast meat is expected to have a pale pink color when it is raw, while thigh and leg meat are expected to be dark red when raw. There are times when poultry meat does not have the expected color, and this has created some special problems for the poultry industry. In addition, raw meat color lightness, which is measured and expressed as the CIE L* value (or L* value), has a close relationship with various physical and chemical properties and functionalities of both raw and cooked poultry breast meat. Poultry meat color is affected by factors such as age of animal, sex, strain (exercise), diet,
intramuscular fat, meat moisture content, pre-slaughter conditions and processing variables. Color of meat depends upon the presence of the muscle pigments myo-globin and hemoglobin. Myoglobin, a protein, is responsible for the majority of the red color. Myoglobin doesn't circulate in the blood but is fixed in the tissue cells and is purplish in color. When it is mixed with oxygen, it becomes oxymyoglobin and produces a bright red color. In addition, the color of meat and poultry can change as it is being stored at retail and in the home. When safely stored in the refrigerator or freezer, color changes are normal for fresh meat and poultry.
Meat tenderness sensation is affected by the presence of several factors, such as fiber resistance, sarcomere length, pH, and collagen morphology environmental stress (hot or cold temperatures) before slaughter, struggle before or during slaughter, stunning method (electrical stunning and vacuum stunning) and post-mortem aging.
Muscles that are deboned during early post-mortem (0 to 2 hours post-mortem) still have energy available for contraction, the meat will be tough. To avoid this toughening, meat is usually "aged" for 6 to 24 hours before deboning (minimum toughness is reached after 18 h in the chicken); however, this is costly for the processor and can increase opportunities for bacterial contamination and growth. The poultry industry has recently started using post-slaughter electrical stimulation immediately after death to hasten rigor development of carcasses and reduce "aging" time before deboning.
Whether or not poultry meat is tender depends upon the rate and extent of the chemical and physical changes occurring in the muscle as it becomes meat. Raw chicken meat is generally very soft and, when cooked, it can even be cohesive. However, a newer emerging quality issue in poultry is the poor cohesiveness of meat related to immaturity on intramuscular connective tissue; it is believed that genetic progress has put more stress on the growing bird and has resulted in histological and biochemical modification of the muscle tissue by impairing some meat quality traits. It has been established that collagen, the major component of the intramuscular connective tissue, plays a key role in determining background toughness of meat of different domestic animals including birds.
Also the rate of pH decline plays an important role on post-mortem meat tenderization and all stages of production; it varies among chicken genetic lines and between individual birds. After death of the animal anaerobic metabolism reduces the pH from about 7.2 in muscle to 5.8 in meat and stiffness develops (rigor mortis).
A fast pH decline, when the carcass has a high temperature, inactivates the calpain system (^ and ^/m — a form only found in bird tissue) and reduce the process of post-mortem tenderization and the meat will be tough. In addition, with a rapid pH decline the myosin will be more susceptible to denaturation, as consequence the meat is characterized as pale and with low functional properties (lower water-holding capacity soft, and exudative) normally refers to the PSE-like condition found in poultry.
PSE, DFD and White Striping a problem in poultry meat. In recent years, there has been concern about the color variation that exists during slaughter and further processing of broiler breast meat. Much of this interest has been on the relationship of variations of extreme meat
Инженерия /Щ
Table 1
Means1 of quality attributes for pale, soft and exudative (PSE), normal, and dark, firm and dry (DFD) fresh meats
Measurement Meat color group
PSE Normal DFD
L* (Lightness) 57.50a ± 1.5 50.16b ± 1.1 43.03c ± 1.2
pH 5.54a ± 0.12 5.91b ± 0.09 6.23c ± 0.10
WHC2 (%) 78.65a ± 2.1 58.81b ± 1.8 24.41c ± 2.4
Cooking loss (%) 9.28a ± 0.9 5.90b ± 1.2 3.09c± 0.8
a row with no common superscript differ significantly (P < 0.05). Adapted from Zhang and Barbut (2005).
colors ranging from very pale (pale, soft, and exudative; or PSE-like) to very dark (dark, firm, and dry; or DFD-like). Various studies indicated that pH-related scattering has a major effect on the translucency of chicken breast meat, causing low pH meat to appear pale with lower water holding capacity, greatest cooking loss and soft texture, and high pH meat to appear dark with higher water holding capacity and lower cooking loss (table 1).
The PSE-like condition is becoming a significant problem in the modern poultry industry (PSE meat has poor characteristics for further processing) with incidences of 5 to 50 % reported for broiler meat and 5 to 30 % reported for turkey meat. For example, some estimates suggest about $ 200 million a year to processors in the US broiler industry alone. The occurrence of PSE poultry meat is believed to be the result of accelerated postmortem glycolysis (rapid pH decline) while the carcass is still warm, especially in some birds that are more susceptible to stress. However, the PSE-like condition has been associated with many factors, including stress, genetic strain, gender, season, geographical region, transportation, pre-slaughter handling, and processing practices. In addition, several studies have been conducted to establish directly or indirectly the main causes of PSE-like condition in poultry. These researches indicated that idiopathic myopathy and an increased susceptibility to stress-induced may have profound implications for meat quality and the incidence of specific conditions such as PSE-like meat. However, no data evidence to support or refute a genetic mutation in chicken and turkey as related to PSE development. Today, with the advent of "omics"
science (Genomics, Proteomics, and Metabolomics) there are more possibilities to further investigate on meat quality abnormalities.
An emerging histopathological changes, very low study until now, is the White striping. It indicates a degenerative myopathy that could be associated with increased growth rate in birds. White striping is a condition in broiler chickens characterized grossly by the occurrence of white striations, seen parallel to the direction of muscle fibers, on broiler breast fillets and thighs. It is characterized on visual evaluation of the intensity of white striping, breast fillets can be categorized into normal, moderate and severe categories. Results from some studies indicate that consumers rejected fillets with white striping at a significant rate, as they were perceived to be high in fat.
However, PSE-like meat, DFD-like meat or White Striping is very important to the processing industry since can translate to a large decrease in profit. Some studies indicate that to predict PSE-like meat or DFD-like meat, color sorting should actually be faster (no need to insert a pH probe and wait for the reading), more convenient (remote color sensing of skinless samples can be used on line) and safer (no cross-contamination due to repeated probe incursion) than measuring pH. Regarding White Striping, the literature suggests that diet (vitaminE deficient, energy, protein, fat, methionine, lysine, etc.) could be a factor for growth causes or striping differences. However, I believe that the White striping could depend to some factors, as genetic pressing, to obtained a higher growth rate of the animals, diet and the stress conditions on which the animals.
