A rapid HPLC method for the extraction and quantification of vitamin B12 in dairy products and cultures of propionibacterium freudenreichii

Abstract

To overcome nutritional vitamin B12 deficiencies in certain populations in Southern Africa, fortified functional foods have been developed. However, current microbiological methods used to accurately determine vitamin B12 levels in foodstuffs, important for quality control and regulatory purposes, are time consuming. This study describes an extraction and detection method for vitamin B12 in dairy products and growth media cultured with Propionibacterium freudenreichii. Samples were extracted by mixing in KCN buffer (pH 4.5), autoclaving at 121 °C for 25 min, cooling and centrifugation. The resultant supernatant was syringe-filtered prior to reversed-phase HPLC analysis using a methanol-water gradient that was effective in resolving the B12 peak. The method offered excellent linearity with a regression coefficient R > 0.998. The limit of quantification was 0.005 μg·mL−1 sample. For samples with vitamin B12 concentrations well within the linear range of the assay, good repeatability was demonstrated for the same sample with mean concentrations of 2.62 ± 0.02 and 2.61 ± 0.02 μg·mL−1 detected on day 1 and day 2, respectively. Recovery values ranged from 98.6% to 103.2%, indicating that the extraction method ensured complete dissolution of vitamin B12 from the matrices under study. Sensitivity was enhanced by sample concentration and purification using a series of solid phase extraction steps which resulted in improved peak resolution and removal of interfering peaks. The method was validated by comparison of the HPLC results of the same sample with those obtained using traditional microbiological methods. The method is a rapid alternative to the more time-consuming microbiological assay.