Research On Chilled Mutton Quality Detectionbased On Low-field NMR Technology

With the gradual expansion of the domestic chilled meat market, the research on the relationship between the quality of chilled meat and the storage environment has become more and more.The purpose of this study is to study the effect of different storage time and storage temperature on the changes of microbial and physical and chemical indexes in the process of storage,Using LF-NMR technique to study the effect of temperature on the water distribution and the changes of moisture transfer in chilled mutton.In addition,The quality analysis model of chilled mutton with different storage temperature is established based on NMR technology.The effects of different modeling methods on the performance of the model are compared,And then selecting the optimal detection model of the quality index of Chilled mutton.The main research conclusions were as follows:(1) Correlation analysis of mutton quality showes that cold storage group (4 C) and freezing group (-18 C) storage time and the total number of colonies,pH b* and TVB-N values are positively correlated (P<0.01),but significantly negatively correlated with a* and L*(P< 0.01).Therefore,the above indicators can be used to evaluate the quality of chilled mutton.The comparison of different storage temperature shows that frozen storage can prolong the storage period of mutton.(2) CPMG pulse sequence multiple exponential decay model is used to determination of the transverse relaxation time (T2) of mutton under different temperature,The results show that there are three kinds of water, combined water, immobilized water and free water,The date indicates that three groups of transverse relaxation times T21,T22 and T23.The results shows that T21,T22and relaxative water content of two and the total took on significant descendent currentwith thechange of cold storage time.meanwhile, free water (T23) also is on the decline, but overall moisture content is on the rise.In addition,there is significan trelativity between T21, T22,T23 and pH and TVB-N of the mutton.(3) The relaxation time of T21, T22 and T23 in cold storage group is lower than that in frozen group (P< 0.05),while T21 and T22 the corresponding proton density are higher than the freezing group, corresponding proton density of the T23 significantly lower mutton frozen group (P< 0.01),May be due to the freezing of the structure of the meat in the freezing and thawing process is damaged,The peak area and the ratio of the peak area and the peak proportion of the immobilized water are significantly decreased, and the free water content is increased.(4) The optimal pretreatment methods is used to compare the performance of cold and fresh mutton quality prediction model with different modeling methods,The results show that PLSR model opimal effect.under 4℃ storage conditions, Rc and Rp are 0.957 and 0.949 of mutton pH quality prediction model; Rc and Rp are 0.991 and 0.952of muttonTVB-N quality prediction model, under -18℃ storage conditions, Rc and Rp are 0.961 and 0.957 of mutton pH quality prediction model; Rc and Rp are 0.956 and 0.949 of muttonTVB-N quality prediction model.Rc and Rp value reach more than 0.9,and the RMSEC and RMSEP values are less than 0.1.Based on low field nuclear magnetic resonance technology,it is feasible to predict the cold and fresh mutton with different storage temperature.