The fluorescence properties of various components,such as casein,butter,vitamin B1,vitamin B2,and vitamin C,in dairy products treated with propidium iodide(PI)dye were examined to assess their effects.Saccharomyces cerevisiae was selected as the target bacterium to investigate bacterial counts using PI fluorescence images in ten dairy products.The findings demonstrated that casein;butter;vitamins B1,B2,and C;and ten other types of dairy products produced fluorescence at an emission wavelength of 615 nm,but they had no effect on fluorescence in S.cerevisiae treated with PI.Bacterial counts were determined in ten dairy products inoculated with 105～107 CFU/mL of S.cerevisiae using PI staining and fluorescence microscopy.The bacterial count results obtained from fluorescence imaging and plate counting were compared.Based on fluorescent image counting,the logarithmic values of the bacterial concentration were 5.69～5.93,6.18～6.28,and 7.13～7.21,respectively,whereas the logarithmic values of plate counting were 5.49～5.63,6.02～6.06,and 7.02～7.06,respectively.The results of the two methods were consistent.Thus,although dairy products and their components emit fluorescence,it does not affect the observation or bacterial counting in fluorescence images when PI is used.
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