Study On Content Of Furosine And Microbial Contamination Of Fermented Milk Retailed

Milk,which is rich in nutrients,is an important part of people's daily diet and has a sustained and rapid growth in the food market.In a wide range of dairy products,fermented milk with good flavor,delicate taste and health care effect is deeply loved by consumers.Natural,probiotic and personalized functional fermented milk has become a focus in recent years.Dairy products need to be heat-treated to kill harmful microorganisms,ensure the safe drinking of consumers and extend the shelf life.Furosine,as an intermediate and end product of Maillard reaction,is produced when dairy products are heated,which is harmful to human health.It is an important index to evaluate the degree of thermal damage.In order to ensure the quality and safety of dairy products and control microbial contamination,the diversity of microorganisms in raw milk has been concerned.In addition,fungi contamination is an important factor affecting the quality and commercial value of fermented milk,which causes a lot of waste every year.It causes huge economic losses to the country and producers.Therfore,the search for chemical preservative substitutes and the development of natural antimicrobial agents have become a focus.In order to solve the problem of overheated processing and fungi contamination of dairy products,it has positive significance to use new cold sterilizated technology and add natural antiseptic spice to develop characteristic fermented milk.The objective was to determine furosine content in fermented milks retailed in China by ion-pair reversed-phase high-performance liquid chromatography(RP-HPLC),which provided theoretical basis for the reasonable regulation and control of hot processing technology of dairy products;the contaminated fungi in different brands of retail fermented milk were separated and purified,microbial diversity in raw milk were analysed;the effects of vanillin on the growth of fungi were studied by plate dilution method,radical colony diameter,and mycelium biomass;in view of two major problems of over heating of dairy products,high content of furosine and fungi contamination,the feasibility of application of vanillin and dynamic ultra-high pressure technology was studied.The research results are as follows:1.Over heating and HPLC determination of furosine in fermented milkAn ion pair reversed-phase high performance liquid chromatography was established to determine the content of furosine of retail dairy products in China.The content of furosine of different dairy products was analyzed(1.16±5.2-1661.05±89.9 mg/100 g of protein).The content of furosine in pasteurized milk was much lower than that in UHT milk.The content of furosine was quite different in low-temperature fermented milk and normal low-temperature fermented milk.It could be attributed to the different heat treatment intensity of dairy products.When the processing time was the same,with the increase of heat processing temperature,the content of furosine in UHT sterilized milk and reconstituted milk increased,and there was significant difference.After 4 hours at 98?,the content of furosine increased greatly,but there was no significant difference in the content of furosine before and after fermentation.At the same time,the protein content of all samples was determined.The order from high to low was concentrated yoghurt,UHT sterilized milk,pasteurized milk,fermented milk,flavored yoghurt and reconstituted milk.2.Molecular diversity analysis of bacterial contamination in raw milk and fungal isolation and identification from contaminated fermented milkThe microbial diversity in raw milk of two samples were analysed.The main bacteria were Acinetobacter,Pseudomonas and Lactococcus.This work aimed to evaluate the microbiological quality of fermented milk of different brands retailed in China and fermented milk self made in lab.Fungal isolates obtained were characterized by DNA sequencing of the Internal transcribed spacer(ITS)region.Among twenty-seven fermented milk samples,about 14.8%of the samples were found contaminated with three different species of fungi.The most predominant type of contaminant was the Cladospoprium spp.In addition,four species of fungi were isolated from the fermented milk self made in lab.Aspergillus,Penicillium and Cladosporium were common contaminating fungi in dairy products.The probability of isolating contaminating fungi from yoghurt with fruit flavor was much higher than that of yoghurt with original flavor.3.Anti fungi activity of vanillin and application of dynamic ultra-high-pressure technology in fermented milkVanillin had significant inhibitory activity on the growth of fungi.A high concentration of vanillin could effectively improve the antimicrobial effect.It could effectively prolong the germination time of spores,reduce the growth rate,increase the lag phrase and reduce the biomass of mycelium.When the vanillin content was 0.2 mg/mL,the inhibition rate of mycelium biomass of Cladosporium was as high as 85.93%,the mycelium morphology is abnormal.The effect of dynamic ultra-high-pressure treatment on fermented milk was studied.The content of furosine of fermented milk treated by dynamic ultra-high pressure increased slightly.The main factors that affected the inhibition effect of fungi were pressure and circulation times.With the increase of treatment pressure and circulation times,the total number of fungi decreased obviously,and the lethal rate increased.Dynamic ultra high-pressure treatment could change the physicochemical properties of fermented milk.The water holding capacity,apparent viscosity and G'G" value of fermented milk increased with the increase of treatment pressure and cycle number.The fermented milk was more stable and the gel strength increased.