| The survey about carcass performances and meat quality of Gannan yak in Gansu, Plateau yak in Qinghai and Sibu yak in Tibet was carried out. Some problems in data collection for Chinese yak industry were found. Two research projects were proposed and carried out. One was establishment of rapid determination methods for yak meat quality; the other was establishment of evaluation system for yak carcass production grading. Two research projects were also verified. Research content as follows:1) Sibu yak also had a significant difference between different genders (p<0.05). There was no significant difference between different genders in Plateau yak. Moreover, it is also found that for Gannan yak ST, BF, SM and QF from hind carcass had nice tenderness, high protein content and moderate water holding capacity with a better quality than muscles from middle carcass. The variability of 34.69% for meat quality of Gannan yak was derived from difference between middle and hind carcass which is closely related to meat chemical composition. But for Plateau yak, PM and LA had a better quality than other muscles. The essential amino acids index of LA for Gaoyuan yak was highest among all muscles with mean value exceeding 155 which is related to higher tryptophan content. For Sibu yak, it was found that there are significant variations during 21d aging for quality traits except b* value. Meanwhile, the changing pattern of quality traits of yak beef with significant change during aging was also investigated through standardization of variables and kinetic model analysis. It was found that quadratic function had best predicting performance on quality traits of yak meat with coefficients of determination, R2, ranged from 0.90 to 0.98, through comparing fitting degree of linear, exponential and quadratic function. The change of pH value, shearing force, press loss and L* were characterized by convex function with positive second derivative, while cooking loss and a* value were characterized by concave function with negative second derivative. It was shown that prolonged aging could be beneficial to improvement of tenderness, but has adverse effects on water holding capacity and meat color.2) Prediction models of physical traits using near infrared spectroscopy were established through partial least squares regression (PLSR) combined with mathematical pretreatments such as orthogonal signal corrections (OSC) and detrending corrections (DT). The coefficients of determination of calibration (R2c) of prediction models were higher than 0.6 except WBSF. The ratio performance deviation for a* and b* values and their derived values SI and HA exceeded 2.0, which are suitable for screening. Through modeling separately for steers and heifers, we found that prediction ability for cooking loss would be increased but for b* would be decreased. Conclusively, near infrared spectroscopy is useful for predicting physical traits of yak meat and could be a potential tool for monitoring beef quality of the yak.3) According to predictive factors critical distribution determined through clustering analysis and confidence interval, four judgment principles for carcass size, which are if round width exceeds 34cm, if EM A exceeds 23 cm2, if round circumference exceeds 48cm and if meat thickness at round exceeds 10cm. Combining age scores with carcass scores, the overall scores could be obtained. Grade I is defined overall score 0-4, Grade II 5-6, Grade II 7-8. Through verification, Samples uniformly distribute in grading range. The cuts total production of yak carcass between different grades is significant, and Grade III> Grade II> Grade I. It has been proven that this grading method could accurately distinguish cuts production of yak carcass. |
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