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Title: Influence of aging days and age at harvest on the meat quality characteristics of Gannan black yak

Author
item WAN, H - Gansu Agricultural Uiversity
item ZHANG, L - Gansu Agricultural Uiversity
item Brown, Michael
item WU, X - Gansu Agricultural Uiversity
item WANG, J - Gansu Agricultural Uiversity
item WU, J - Gansu Agricultural Uiversity

Submitted to: Journal of Animal and Veterinary Advances
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/20/2010
Publication Date: 4/12/2011
Citation: Wan, H.L., Zhang, L.P., Brown, M.A., Wu, X.J., Wang, J.H., Wu, J.P. 2011. Influence of aging days and age at harvest on the meat quality characteristics of Gannan black yak. Journal of Animal and Veterinary Advances. 10(9):1089-1096.

Interpretive Summary: The yak species (Bos grunniens) represents a unique and economically important bovine species found mainly on the Qinghai-Tibetan plateau of China at altitudes of 3,000 m above sea level. Yaks are used for meat, milk, draft, and fiber and are a major economic resource for herders in this region. Yak meat has gained additional recognition in the recent years because of its good quality, high protein and low fat content, and favorable amino acid and fatty acid profile compared with Bos taurus cattle, and because of its good reputation in food safety. However, yaks are usually harvested at older ages and sold on the commercial market without any distinction being made on age at harvest. Research on various species has indicated that meat eating quality and muscle chemical composition vary with increasing animal age at harvest irrespective of sex, breed or species. Because of the relationship between age at harvest and tenderness, this has led to widespread opinion that meat derived from yaks is less tender upon consumption after cooking. It is well established that aging meat in the cooler produces favorable changes in meat characteristics, and the optimum aging time depends, among other factors, on the breed and the age at harvest. However, limitations on cooler space in commercial packing plants make it difficult to hold product for any extended time, so aging time is often limited. Research was initiated at Gansu Agricultural University in cooperation with USDA-ARS, Grazinglands Research Laboratory to determine optimal aging times for different ages of yak. Results from the research demonstrated that aging days appeared to be more influential on shear force than age of yak at harvest and tended to moderate the age at harvest effect on shear force within the yak species. Consequently, aging may be a valuable tool for making a more consistently tender product in yak for the consumer and increasing its market value. Seven days of aging appear to be sufficient for production of tender meat and other quality parameters seem to be similar or better than other postmortem aging days.

Technical Abstract: Meat from yak (Bos grunniens) is a primary staple in diets of people in western China. Yak meat has low-fat content, high protein and good amino acid and fatty acid profiles. However, there is evidence that meat from yak is less tender than meat from Bos taurus cattle. Gannan Black yaks (n=181) were used to investigate the effects of age at harvest and aging days on meat quality characteristics of M. longissimus dorsi. Yaks were harvested at 2, 3 and 4 yr of age, and muscles of each yak carcass were aged for 0, 1, 3, 7, 14 or 21 d at 4 deg C and frozen at -20 deg C until analyzed. Age at harvest affected shear force and percentage fat, protein, and moisture (P < 0.05). Aging days affected shear force, dry cooking loss, pressing loss, moist cooking loss, pH, percentage fat, moisture (P < 0.01) and protein (P < 0.10). There were interactions between aging days and age at harvest for shear force, moisture and protein (P < 0.01). Aging days appeared to have a greater e'ect on shear force than age at harvest and tended to moderate the age at harvest e'ect on shear force. Dry cooking loss and pressing loss decreased until 3 days postmortem after which it remained relatively constant. Meat aged 7 days had the lowest moist cooking loss (P < 0.05). After thawing, pH decreased during the 21-d period of postmortem aging with the greatest decline in the first 24 h (6.68 at 2 h postmortem to 5.73 at 24 h postmortem). Results suggest that aging yak meat 7 d is sufficient for acceptable tenderness and meat quality.