Evaluation of Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry for Rapid Identification of Bacteria in Processed Soybean Products

Abstract

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) has recently been demonstrated as a rapid and reliable method for identifying bacteria in colonies grown on culture plates. Rapid identification of food spoilage bacteria is important for ensuring the quality and safety of food. To shorten the time of analysis, several researchers have proposed the direct MALDI-TOF MS technique for identification of bacteria in clinical samples such as urine and positive blood cultures. In this study, processed soybean products (total 26 test samples) were initially conducted a culture enrichment step and bacterial cells were separated from interfering components. Harvested bacterial cells were determined by MALDI-TOF MS and 16S rRNA gene sequencing method. Six processed soybean products (23%) were increased bacterial cells after culture enrichment step and they were successfully obtained the accurate identification results by MALDI-TOF MS-based method without colony formation.

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

“…E. coli could be correctly identified when present at a minimum of 10 7 CFU/mL (Table 2). This result indicates an improvement in the identification limit was obtained compared to previous results (Furukawa et al, 2013). K. pneumoniae and C. freundii could also be identified with adequate identification scores when present at the same concentration (data not shown).…”

“…After anionic surfactant treatment (0.5% SDS), accurate identification scores were obtained using soy milk samples with up to 70% fat content (Table 1). When using a previously described method for removing proteins from soy milk (Furukawa et al, 2013), MALDI-TOF MS scores were less than 2.0 when the fat content of soy milk samples was 50% and greater. This indicated that residual fat matrices may have interfered with the raw mass spectra and affected spectrum matching.…”

“…The harvested coliforms cells were washed twice with SDS solution to ensure complete removal of fat matrices. Coliform pellets were suspended in 0.3 mL of sterile water and used for MALDI-TOF MS and 16S rRNA gene sequencing; 16S rRNA gene sequencing was performed as described previously (Furukawa et al, 2013).…”

“…Moreover, it is difficult to detect and identify bacteria in foods that contain fat matrices (Schrader et al, 2012;Gadkar and Filion, 2013). In particular, there is little information regarding non-culture-based identification of bacteria in food samples using MALDI-TOF MS (Ferreira et al, 2010;Barreiro et al, 2012;Furukawa et al, 2013).…”

Rapid Detection and Identification Systems for the Microbiological Assessment of Processed Soy Foods: A Review

“…However, it is difficult to detect and identify bacteria in high lipid-containing food. Moreover, little information is available on non-culture based bacterial identification in food samples using the MALDI-TOF MS (Barreiro et al, 2012;Ferreira et al, 2010;Furukawa et al, 2013;Katase & Tsumura, 2014).…”