Rapid Determination of the Folic Acid Content in Milk Powder by Microbial Impedance Method
In order to establish a new method for rapid determination of folic acid content in milk powder based on microbial impedance method,the test made a standard series of tubes based on the first method of the national standard GB 5009.211-2022,and optimized the determination conditions of the series tubes,the standard curve of microbial impedance method was established through exploring the linear relationship between the impedance changes of bacterial bodies in various series of tubes and the folate content.And then using milk powder quality control samples and commercially available milk powder as test samples,the detection performance of this method was evaluated.The results showed that when the standard series of tubes were cultured for 20 h and subjected to centrifugation and ultrasonic fragmentation treatment,the linear relationship between the resistivity value of the measured bacterial body and folate content between 0.000 ng/mL and 0.100 ng/mL was the best.The fitted standard curve equation was Y=8866.3X+177.38,with a correlation coefficient of R2=0.9952.The limit of detection was 1.26 μg/100 g,the limit of quantification was 4.20 μg/100 g,and the recovery was 96.2％-103.6％.The relative standard deviation(RSD)values for quality control samples of milk powder and four commercially available milk powders ranged from 3.4％to 6.4％,and the total detection time was about 3 d.Compared with the national standard method,this method has comparable repeatability and accuracy,but with shorter detection time,which can quickly determine the content of folic acid in milk powder.
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