Abstract: Ripened cheese is apt to produce biogenic amines that have a detrimental impact on human health. In this study, the contents of biogenic amines in hard cheeses made from yak’s milk were determined using high-performance liquid chromatography (HPLC) and high-throughput sequencing technology in order to evaluate the quality and safety of cheese. The results indicated that putrescine, 2-phenylethylamine, tyramine, cadaverine and histamine were detected as the major biogenic amines in the cheeses. The content of each biogenic amine increased significantly with increasing ripening period from one to six months. The levels of histamine, tyramine and total biogenic amines were the highest after ripening for five or six months, below the recommended safe limits (50, 100 and 1 000 mg/kg respectively) throughout the ripening process. The content of total free amino acids had positive correlations with the contents of each biogenic amine except histamine and total biogenic amines and with the ripening time (P < 0.01, P < 0.05). Similarly, there was a positive correlation between all biogenic amines. The major bacterial genera were Streptococcus, Leuconostoc, Lactobacillus, Raoultella, Acinetobacter, Pseudomonas, Enterobacter and unclassified_Enterobacteriaceae in all cheese samples. In addition, Streptococcus was the dominant genus with an average relative abundance of 84.63%, followed by Leuconostoc with an average relative abundance of 6.91%. The relative abundance of each genus varied depending on the ripening period. These results will provide a theoretical basis for evaluating the quality and safety of hard cheese made from yak’s milk and shedding light on the formation mechanism of biogenic amines.

Key words: yak’s milk; hard cheese; biogenic amines; composition of bacterial community