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In Thailand, more than half of the slaughtered mature cattle are culled cow including 25% culled dairy and about 50 older Thai native cattle. However, culled dairy cows are often in poor body condition and have to be fattened to improve the available cash of farmers (Little et al., 2002). Under farm condition, lactating cows could usually be in poor body condition. Short-term fatten of culled cows increases their salvage weight and offers marketing alternatives to commercial beef cattle producers.
It is well known that beef from older culled animals is tougher (Bouton et al., 1978) and tend to be drier upon first bite, with a meatiness residue, compared to meat from young animals (Shorthose and Harris, 1990). Hill (1966) found that the effect of collagen on tenderness was due to the soluble part of total collagen, where solubility decreases with increasing age. Several studies have evaluated the efficiency of increasing live and carcass weights of culled dairy cows with high-concentrate diets (Miller et al., 1987; Cranwell et al., 1996 and Vestergaard et al., 2007). This improved their condition score and fatness state (Vestergaard et al., 2007). Finishing culled dairy cows can be an important activity to raise the profits of cattle farms, but this requires the feeding costs and limited period. In this study, we therefore interested in the utility of by-products from the agro-food industry like cassava pulp and rough rice bran. In Thailand, cassava starch is a large and growing industry generating at least 1 million tons of pulp annually (Sriroth et al., 2000). Cassava pulp is consisting of the solid waste produced by the cassava starch industry. As it still contains high amounts of starch (50-60% of dry matter), it is a feed with a high energy content. Like for cassava, Thailand is one of the world's largest producers of rice. Rice bran is the pericarp and
germ of Oryza sativa seeds and constitutes about 10% of the whole rice grain. The current main application for cassava pulp and crude rice bran is as a low price animal feed in the beef cattle industry. Of all the meat traits, tenderness is considered to be the most important with regard to eating quality (Miller et al., 2001). Various pre- and post-slaughter factors and their mutual effects in¬‚uence tenderness of meat (Destefanis et al., 2008). The most important pre-slaughter factors include: age, species, sex, breed, feeding of animals and degree of stress prior to slaughter. Post-slaughter transformations, including rigor mortis and proteolysis have a crucial in¬‚uence on meat tenderness. The post-mortem process of storing meat post-rigor for various lengths of time under adequate conditions of temperature to improved meat quality is known as conditioning or aging (Boakye and Mittal, 1993). Aging is a method often used to improve meat tenderness. The aging methods used in red meats include vacuum aging, dry aging, time course of aging, heat accelerated aging and enzymatic aging (Pearson, 1987). Post-mortem aging is a natural process which improves the palatability attributes of meat. Aging process could be attributable to two types of processes; dry and wet aging, Dry aging is the traditional process but wet aging is the aging meat in vacuum bag and keep under refrigerated area. Aging process changes in the connective tissue component of the meat or weakening of the myofibrils (Warriss, 2000). Nishimura et al. (1998) suggested two phases in which conditioning takes place. The first phase occurs at a rapid rate and is the denaturation and proteolysis of key myofibrillar and associated proteins (Jiang, 1998). The slower second phase involves the structural weakening of the intramuscular connective tissue (Nishimura et al., 1998). The mechanisms involved in the meat tenderizing process are considered to be the results of the activities of endogenous proteolytic enzymes present in the muscles. The tenderizing effect of aging is more evident in carcass from older animals than in the usually more tender lean meat from younger animals. Aging, therefore, refers to holding of meat at refrigerated temperatures for an extended period to allow natural enzymatic reactions to take place to enhance tenderness and flavor, thus allowing proteolytic enzymes to break down some of the complex proteins contained in the muscle (Goll et al., 2003). Koohmaraie (1994) also indicated that in red meat post-mortem proteolysis is responsible for increasing the ease of fragmentation of Z-disks and other muscle proteins. In addition to proteolysis, the increase in post-mortem ionic strength due to decreased protein interactions and increased solubility of myofibrillar proteins contributes to aging induced tenderness (Wu and Smith, 1987). However, the cost of storing the meat at refrigerated temperatures is high. These expenses include the storage space, refrigeration and the inevitable weight loss from the surface of the carcass due to the evaporation of water or the loss of exudates from butchered joints (Warriss, 2000). Therefore, several methods have been developed to minimize the time in storage but not impair the meat quality, especially tenderness.
Many studies have shown that tenderness is dependent on such enzymes as: cathepsins and calpains. Some researchers suggest that proteasomes may be responsible for the ¬nal tenderness (Bernard et al., 2007 and Kemp et al., 2010). The calpain system consists of two calcium dependent enzymes (calpain I and calpain II) and a specific inhibitor; calpastatin. In a muscle, calpains are located in the cytoplasm and cell membranes. The calpain II is in majority located in the cytosol, whereas the calpain I is in 70% bonded to myo¬brils (Xian-Xing et al., 2009). The activity of the system of calpains depends on many factors such as: pH, temperature and the concentration of calcium ions (Steen et al., 1997 and Goll et al., 2003). For these reasons, many researchers try to improve meat tenderness by infusing whole carcass or injecting a portion of a carcass with a CaCl2 solution within 1 h post-mortem (Wheeler et al., 1997; Lawrence et al., 2001 and Jaturasitha et al., 2004).
Notwithstanding, meat purchasing decisions are influenced by color more than any other quality factors because consumers use discoloration as an indicator of freshness and meat quality. Otherwise, the ability of fresh meat to retain moisture is arguably one of the most important quality characteristics of raw products. Water is the major constituent of meat accounting for approximately 75% of its weight (Tornberg et al., 1993). The ability of meat to retain inherent water, also defined as water - holding - capacity (WHC) is an essential quality parameter for both industry and consumer. For the meat industry, low WHC implies decreased business profit and influence the sensory quality of meat for the consumers. However, some research has shown that chloride can induce discoloration (Kerth et al., 1995) and dramatically decrease water holding capacity of meat (Wheeler et al., 1997).
Therefore, the present study was conducted in order to achieve the following aims
To investigate the effect of including these by-products into the finishing diets of culled dairy cows on carcass and meat quality.
To determine the effect of aging and calcium chloride injection on color, water holding capacity, pH, lipid oxidation, shear force value, myofibril fragmentation index and sensory evaluation of culled dairy cows meat.