High-Throughput Identification of Coliforms in Processed Soybean Products Using Matrix-Assisted Laser Desorption Ionization Time-of-Flight Mass Spectrometry

Abstract

Standard methods for bacterial identification include culturing and biochemical identification. These methods are time-consuming because they require culturing in different media for at least a few days. Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) has recently been demonstrated as a rapid, reliable method for bacterial identification. In this study, we developed an improved sample preparation method to accurately identify coliforms in processed soybean products using MALDI-TOF MS. Our method included harvesting bacterial cells using isoelectric precipitation and anionic surfactant treatment to eliminate food matrices such as proteins and fats. At least 10⁷ colony-forming units (CFU) / mL of typical test strains of Escherichia coli, Klebsiella pneumoniae, and Citrobacter freundii were successfully identified in soy milk samples. After sample incubation steps at 37°C for 18 h, low levels of coliforms (10¹ CFU/mL) could be identified. Our proposed procedure was verified by accurately identifying coliforms in commercial processed soybean products.