Dipicolinic acid contents used for estimating the number of spores in raw milk

摘要

A new rapid detection the number of spores method had been developed in raw milk through analyzing dipicolinic acid. The method was based on the concentration of DP A in raw milk which was converted into endospore numbers using endospore forming pure cultures as standards. To increase the detection limit the extraction of DPA from endospores in raw milk was optimized. The results showed adding 0.5 mL of the 0.1 mol L-1 DTT solutions into centrifuged raw milk (4 mL containing spores) and incubating at 25°C for 30 min, then adding 2 mol L-1 HC1 at boiling water for 30 min, the concentration of DPA was highest. The relationship between the absorbency (expressed in DPA) and the counts of spores was established. And the regression equation was obtained that is y=0.1087 x-0.3182, R2=0.7842. Thus, the methods of detection spores were ascertained in skim milk. The detection limits were 1.46×103 CFU mL-1.