Evaluations and analyses of pollution factors of yogurt quality and safety in Lhasa

Objective  To evaluate and analyze the key pollution factors affecting the quality and safety of yogurt collected by different production methods in four different districts (Chengguan District, Maizhokunggar County, Linzhou County and Damxung County) of Lhasa in Tibet, and provide strong data support for improving the quality and safety of Lhasa yogurt and strengthening the quality and safety supervision.

Method  In 2018, 106 yogurt samples with different production modes were collected from four counties (districts) of Lhasa, including 22 samples from Linzhou County, 40 samples from Chengguan District, 23 samples from Maizhokunggar County and 21 samples from Damxung County. Eight samples were collected from enterprises, 54 samples from individual workshops and 44 samples from families. Five kinds of heavy metals, aflatoxin M1 and six kinds of microorganisms in yogurt samples were detected and analyzed by ICP-MS, HPLC-MS, microbial culture and separation, respectively to evaluate the quality and safety.

Result  Total 106 yogurt samples were seriously contaminated by mold, and the exceeding rate was 46.23%. Shigella, Salmonella and aflatoxin were not detected in yogurt. The detection rate of Staphylococcus aureus in yogurt produced by individual workshop was the highest at 25.93%. Pb was the main heavy metal pollutant in yogurt produced by farmers and herdsmen, individual workshops and enterprises, with the contamination contribution rate of 42.5%. The content of Cr in yogurt of Damxung County was higher than those in other three counties (districts), with the exceeding rate of 19.0%. The contents of Pb and As in yogurt of Chengguan District were higher, with the exceeding rates of 15.0% and 2.5%, respectively. Pb was also the main heavy metal pollutant in yogurt of Linzhou County, Chengguan District and Maizhokunggar County, among which the contamination contribution rate of Pb in Chengguan District was the highest reaching 54.02%.

Conclusion  The pollutions of heavy metals and molds in yogurt of Lhasa are prominent, which should be paid attention. The special natural environment in Tibet is not conducive to the mildew of feed, so no aflatoxin is detected.