Composition and Nutritional Value of Different Raw Poultry Meats. From USDA (1999b).

A Comparative and Approximate Gross Composition of Muscle, Fat, and Bone

WATER HOLDING CAPACITYMost poultry products contain 6080% moisture that is held by the protein matrix. The amount of protein is usually around 1020% of the product. In certain countries, such as Canada, a minimum of 11% protein is required to be present in various processed meat products, where 9.5% should be meat proteins; otherwise, words like imitation should be included in the products name. The other major component is fat, which usually ranges between 535%. However, fat does not contribute to water-holding capacity, and sometimes high fat products show poor moisture holding, as will be discussed later. Therefore, obtaining protein with good functional properties is of paramount importance. The quality of the proteins, in terms of water-holding capacity, is influenced by the type of muscle, pre- and post-rigor conditions (DFD and PSE meat), and processing treatments such as freezing (i.e., freezing would usually have a negative effect on water-holding capacity). Determining the water-holding capacity is important for fresh meat cuts sold directly to the consumer and for further processed products prepared by the industry. In both cases, high yield and low cooking losses are desired. Consumers shy away from packages of fresh meat showing free fluid surrounding the cuts. This is also true for cooked products, such as frankfurters, showing exudate in the package.

Meantime, the Water-holding capacity is an important meat quality attribute because juiciness (a sensory attribute) and tenderness are partially dependent on the ability of the meat to retain moisture under normal storage conditions and during thermal processing (Jeffery, 1983; Lawrie, 1998). Juiciness, an indicator of water-holding capacity, is important in meat tenderness because it provides lubrication to consumers as they chew the meat. Improvements in body weight do not appear to be associated with increased body water retention. The reduced water-holding capacity of the meat is the result of protein damage from the low pHcondition of the muscle early after death. It is thought that this damage is at least partially reversible by adjustment of pH or ionic strength in the meat through the use of salts, phosphates, or other ingredients. Regardless of how or why it occurs, processors are faced with defective meat and want to know what they can do to use it in their products without sacrificing yield or quality. Extreme cases produce up to a 20% purge loss in a cook-in bag and cook losses over 30% from a breast fillet. An additional defect is that the poor protein function in PSE meat causes poor binding of meat pieces in formed products, a condition called cracking. Furthermore, defective cook-in bag products need repackaging, which increases costs further. There are limited strategies for dealing with defective meat.

POOR WATER HOLDING CAPACITY FAULTSANTEMORTEM Transportation Stress Transportation is another potential stress associated with meat quality problems. Transportation stress is very complex because it not only includes the act of transporting (vibration and noise) but also thermal stress, relative humidity, airflow, and crowding. Turkeys and broilers are often transported to processing plants for 30 min to 3 h prior to processing. The transportation process can be stressful to the birds and thus may affect meat quality. However, research related to transportation stress and meat quality in poultry is not conclusive. Results have shown an improvement, no change, or a decrease in meat quality factors such as color and water-holding capacity (van Hoof, 1979; Kannan et al., 1998; Owens and Sams, 2000; Debut et al., 2003). These studies have varied under numerous conditions, including time, processing methods, environmental temperatures, and stocking density. However, based on research in swine and poultry, it can be concluded that there is potential for transportation to lead to increased postmortem metabolism, which can ultimately affect meat quality. Therefore, it is important to be aware of conditions that may lead to stressful situations for the birds, such as crowding, elevated temperatures, and transportation duration. POSTMORTEM The water-holding capacity of meat is reduced by internal forces exerted by pH or shrinkage and disintegration of membranes and by external force (Honikel, 2006). Then some water is released from the muscle as a drip loss. The amount of water released depends on the extent and rate of pH drop. Soluble compounds such as sarcoplasmic proteins, peptides, free amino acids, nucleotides, nucleosides, B vitamins, and minerals may be partly lost in the dripping, affecting nutritional quality (Toldra and Reig, 2006): The meat in general has less pH-induced shrinkage (higher water-holding capacity and firmer structure), which leads to a darker color (no denaturalization, higher oxygen binding). The water-holding capacity is obviously decreased, as meat ultrastructure (i.e., myofibrils, filaments, muscle fibers, etc.) undergoes size shrinkage; also, on the muscle periphery, potassium accumulates in the dehydrated fibers, altering the muscle chemistry.

Lower pH levels in the muscle are associated with lower water-holding capacity, due to alterations in the structure of myofibrils within the muscle when in a low-pH environment. If a muscle can hold more water, it typically will be lighter in color. Broilers produced by organic methods had a lower pH and a lower water-holding capacity, which may have been responsible for producing meat that appeared more yellow as well as less red than broilers produced by a traditional system (Castellini et al., 2002). The defect PSE affects not only color negatively, but also meat texture and integrity. Slow, inadequate chilling decreases the pH of the meat from lactic acid buildup and begins to denature proteins within the muscle. Meat quality as well as water-holding capacity begins to decline, which can make meat tough. To minimize the occurrence of PSE, the temperature of the carcass should be lessthan 25C by 60 min postmortem (Alvarado and Sams, 2002).

PSE CharacteristicsTypical characteristics of PSE poultry meat have been reported by a number of researchers (Owens et al., 2000a; Van Laack et al., 2000; Woelfel et al., 2002; Zhang and Barbut, 2005a) (see Table 1). In PSE meat, the pH is generally low (pre- and postrigor), due to accelerated postmortem glycolysis. This low pH causes lower water-holding capacity in the form of higher drip losses, higher cooking losses, and higher expressible moisture, because more water is contained in the extracellular space than in the intracellular space (Swatland, 1993). Barbut et al. (2005) evaluated the microstructure of PSE meat and found more intercellular open space compared to that in fillets considered normal, or dark, firm, and dry (DFD) meat. These open spaces may contribute to the lower water-holding capacity that is typically observed with PSE meat, especially drip loss. Furthermore, color is also affected because with more water in the extracellular space, light will be reflected rather than absorbed (Lawrie, 1998). Therefore, PSE meat is pale or has high L values (an indicator of lightness). Muscle pH is highly correlated (r = 0.7) with the L value, and the pH and L values are moderately to highly correlated with measurements of water-holding capacity (Barbut, 1993, 1997; McCurdy et al., 1996; Owens et al., 2000a; Van Laack et al., 2000; Woelfel et al., 2002). Because of its high correlation with pH and waterholding capacity and its relative ease of measurement, the L value, or color, has been recommended as a tool used to classify meat into PSE and normal categories. The high incidence of PSE meat in the poultry industry can result in significant economic losses to processors, due to the loss of water-holding capacity, change in color, and change in texture, especially in products processed further (Owens et al., 2000a).

Reference Values Normal and PSE Meat Parameters

Preslaughter stresses can also cause PSE. In a study conducted by Zhang and Barbut (2005), boneless, skinless chicken breasts with PSE meat were collected at 10 different times from a deboning line of a commercial processing plant. Breasts with PSE lost 30 and 66% more moisture when cooked than did meat not having PSE. All texture profile values were lower for PSE meat than for dark, firm, and dry (DFD) meat and the rigidity of elastic (G _) values indicated that PSE meat formed softer gels when cooked. Freezing enhanced the structural differences between the two types of meat, and analysis results indicated that PSE meat was more severely affected by freezing than was DFD meat (Zhang and Barbut, 2005). The decline, and the rate of decline, in pH are important because these changes can affect many meat quality attributes, including color, water-holding capacity, and texture. POULTRY MEAT PROCESSING FAULTS / ISSUES :

Kinfes over-heating during meat chopping and grinding . The relative humidity in the cooler is usually kept high so as to minimize shrinkage due to high evaporation losses resulting from cold air blowing over an unwrapped product.

Attention should be given to allow enough spacing between the parts (positioned on trays or in boxes) so cold air movement will not be restricted, and the desired chilling rate will be achieved.

MOISTURE MIGRATION FROM THE PRODUCT: Moisture migration from the product interior depends on product temperature, composition, moisture content, and product water-holding capacity; moisture evaporation

from the product surface is the differential in moisture between that of the product surface and that of the drying medium.

WATER HOLDING CAPACITY TESTSMeat Parameters to be evaluated 24h after slaughter: pH, lightness (L) redness (a) yellowness ( b) water holding capacity.

Water Holding Capacity Evaluation Water holding capacity should be evaluated using a method adapted from Hamm (1960), based on meat water loss when pressure is applied on the muscle. Meat cubes weighing 2g were laid between two filter paper circles placed on glass plates, on which a 10kg weight was put for 5min. Samples are then removed from thefilter papers, and weighed. Water loss is calculated as the weight difference between initial and final weight. Results are expressed as the percentage of drip loss relative to initial sample weight.

NUTRITIONAL STRATEGIES TO IMPROVE THE WHC: Use of Sodium Bicarbonate to balance the DEB Analysis of K in soybean meal is important to establish correct values to be used in calculating DEB.