| Tan sheep is a representative livestock in Ningxia area. The meat is tender, juicy and delicious, and the smell of the mutton is weak. It has great potential for processing, being used for food as well as for commerce. As Global Wealth Report published by Swiss Credit Bank indicates, the middle class in China has exceeded 109 million in 2015. The consumption of middle class will be great driven force to develop high quality goods. Tan mutton, with many good qualities can satisfy the demands of middle class that fast moving consumer goods should be expensive and valuable. Therefore, the key point in exploring the commercial value of Tan mutton is to realize the rapid transportation to advanced areas in China. Ningxia lies in the center area of China and it is more than a thousand kilometers away from the developed areas along the seas in the eastern areas, so the cold chain logistics can be hardly realized, and the freeze-thaw conditions which have less influence on the quality and flavor of Tan mutton need to be developed. Pre-study in theory has been done in this paper on the freeze-thaw conditions for Tan mutton.The physicochemical indexes of Tan mutton frozen in still air under different temperatures at-30℃,-40℃,-50℃,-60℃ and-70℃ had been compared firstly. The results showed that except cooking loss, Tan mutton’s pH value, water holding capacity, juice loss, meat color and shear stress had all been obviously influenced under different freezing conditions. Through the analysis of the major components, the evaluation model of freezing conditions of Tan mutton had been got, namely K=80.125K!+15.638K2. By calculating the scores of different freezing methods, the -60℃ freezing condition by static air was proved to be the best freezing method for Tan mutton.Then, the low field nuclear magnetic resonance was adopted, and the differences of the moisture distribution and the water retention of Tan mutton under still air at 25℃,10℃ and 58℃ were studied. By comparing with chilled Tan mutton, the relaxation time of the water which was hardly to flow decreased obviously in the Tan mutton by freeze-thaw process, and the relative amount increased evidently, while the relaxation time of free water had been distinctly increased, and the relative amount decreased evidently. By comparing the Tan mutton thawed under different temperatures, the relaxation time of free water in Tan mutton had significant increased as the thaw temperature went down. Considering the change of hydraulic and pressurized water loss rate, relevant analysis concluded the water retention of Tan mutton increased as the thawing temperature decreased within a certain range.At the last stage, the headspace solid-phase micro extraction and the gas chromatograph-mass spectrometer (SPME-GC-MS) was exerted to further explore the influence of thawing condition on the flavor of cooked Tan mutton. The results indicated that freeze-thaw operation leaded to the decrease of the kinds of volatile flavor compounds in cooked Tan mutton. The kinds of flavor compounds in cooked Tan mutton had obviously increased as the thawing temperature decreased. A conclusion had been drawn that freeze-thaw process could not add the varieties of flavor substances from the analysis of specific volatile flavor compounds. Through the principal component analysis and cluster analysis, the flavors of cooked Tan mutton were composed of eight volatile flavor compounds, and they could be classified into three kinds. They were separately Acid, Ester, Heterocyclic Compounds and Alcohol, Aldehyde, Ether and Ketone, as well as Hydrocarbon. |
