Abstract: China is the largest producer and consumer of pork meat in the world, and the quality as well as safety of pork meat has been an issue of public concern. However, freshness of pork meat is a rather complex concept, which includes different microbiological, physicochemical and biochemical attribute. Therefore, it has important significance to monitor the quality of freshness for pork meat due to the positive position in our life. At present, quality control in the meat industry is mostly tested by two methods. One is the measurement of viable bacterial counts, the other is a sensory test by experts. The former is a very objective method, but it takes 2-5 days and more days to obtain results. This means that the method cannot simultaneously evaluate meat freshness when the meat is sold. The latter is a very rapid method. However, it is very difficult to evaluate slight differences in the meat freshness before the initial stage of putrefaction. Therefore, it would be important to develop novel methodologies for the rapid monitor the quality of pork meat.
A contemporary revolution, ambient mass spectrometry was raised by the Cooks et al, which enabled the ionization of samples in their native environment without sample pretreatment or minimal sample pre-treatment was developed. After the emergence of the pioneered technique, desorption electrospray ionization, more than 20 direct-ionization techniques have been developed. Among these techniques, several ionization methods including direct analysis in real time (DART), desorption atmospheric pressure chemical ionization (DAPCI), dielectric barrier discharge ionization (DBDI), plasma assisted desorption ionization(PADI) et al, were based on the atmospheric plasmas. In particular, DAPCI-MS has been well demonstrated as a noninvasive analytical method of high sensitivity, good chemical selectivity and fast analysis speed. To date, DAPCI-MS has been successfully applied for trace analysis in food safety forensic science, environmental science, pharmaceutical analysis and plant science.
In this study, the spectra fingerprints of pork meat were detected by DAPCI-MS in the positive ion mode with different days without any pretreatment to the samples. Together with further principal component analysis (PCA), the raw data from DAPCI-MS were successfully applied to probe the differentiation for pork meat freshness. The result shows that DAPCI-MS is a speed, sensitivity and selectivity tool for analysis of pork meat in different days. According to the spectra fingerprints by DAPCI-MS, the freshness of pork meat was divided into three degree. Decomposition and metabolites including serine, glycine, indol, 2,3-butanediol, trimethylamine can be used as a key for the evaluation of the freshness of pork meat. Classification and identification of pork meat freshness and the reproducibility of the method were further realized by PCA and CA. This method can not only be used for the rapid evaluation of pork meat freshness with high tolerance, but also is very promising tool for rapid analysis of highly complex viscous samples.