Evaluation Of The Bacterial Contamination In Goat Milk Powder Using PacBio SMRT Sequencing Technology

Along with the improvement of people’s living standard and nutrition consciousness,goat milk and milk powder products have raised much popularity by consumers because of its rich nutrition.The effective control of bacterial contamination as a key element of quality control is of significance for ensuring product safety during the goat milk powder production.As the common sterilization method,heat treatment can kill most microbes.However,the presence of a large amount of heat-resistant bacteria and inactivated bacterial enzymes affect the flavor,solubility and shelf life of goat milk powder,causing the increasing of food safety risk.Therefore,it is necessary to evaluate all bacterial contamination,including activated and inactivated bacteria in goat milk powder,as well as the better assessment method for bacterial contamination.In this study,the value of WPNI,lipase activity and protease activity in 7 samples of goat milk powder were measured.Pacific Biosciences(PacBio)single-molecule,real-time(SMRT)sequencing technology,droplet digital polymerase chain reaction(ddPCR)and live bacteria counting were applied to evaluate bacterial contamination.The main results were listed as follows:Both the total number of colonies and the viable bacterial counting in relation to common pathogenic bacteria were in line with the national standards.And the value of whey protein nitrogen index(WPNI)was less than 6 mg/g,indicating the higher heat treatment in goat milk powder.But there were still a certain activity of lipase and protease in goat milk powder.There were 10 phyla,119 genera,and 249 species were identified.The major bacteria phyla were Firmicutes(82.90%)and Proteobacteria(16.53%).Bacillus(42.21%),Paenibacillus(22.14%),Lactococcus(6.16%)and Cronobacter(4.46%)were primary genera.At species level,Bacillus cereus(31.82%),Lactococcus lactis(5.09%),Alkaliphilus oremlandii(4.17%)and Cronobacter sakazakii(3.76%)were dominant.It is consistent with the absolute quantification results of ddPCR,which were 63291.43 and 10078.57 copies/g for Bacillus cereus and Cronobacter spp.,respectively.Common pathogenic bacteria,such as Salmonella,Escherichia coli and Staphylococcus aureus were almost undetected by ddPCR,which is in line with the results of PacBio SMRT sequencing.In addition,Bacillus was positively correlated with lipase and protease activity,and was negatively correlated with WPNI,especially in Bacillus cereus.Therefore,we should take into account that the risk control of contamination of Bacillus cereus and Cronobacter spp.during the processing of goat milk powder.For example,shortening the storage time of raw milk and milk after pasteurization,cleaning equipment and pipelines according to the national standard,as well as ensuring the hygiene conditions of operators and environment.This study suggested that PacBio SMRT sequencing technology could provide an idea of objective evaluation of the bacterial contamination and help to better realize the quality control of goat milk powder products and the prevention of food safety risks.