33-4

Y. BURGULA, S. Kim, B. L. Reuhs, M. A. Cousin, and L. J. Mauer. Dept. of Food Science, Purdue Univ., 745 Agricultural Mall Drive, West Lafayette, IN 47907-2009

Recent advances in Fourier Transform Infrared Spectroscopy (FT-IR) and chemometrics software have resulted in a renewed interest in using FT-IR spectroscopy as a non-destructive method for identifying and classifying intact microbial pathogens in food matrices. The primary requirement is to obtain a representative sample of food matrix containing the pathogen of interest, collecting FT-IR spectra and analyzing spectra using chemometrics to distinguish between microorganisms. A method was recently developed to improve the sensitivity and specificity of detection of Salmonella Typhimurium and E. coli O157:H7 from Tryptic Soy Broth (TSB) using FT-IR. The objective of this research was to extend this application to distinguish between E. coli O157:H7 and E. coli K12 in a fruit juice matrix using chemometrics. E. coli O157:H7 and E. coli K12 were cultured to a concentration of 10⁹ CFU/mL in TSB. The bacterial cells were then centrifuged at 5000 RPM for 10 min followed by washing with distilled water twice to remove any interfering metabolites. The cell pellets were re-suspended in 8 different types of fruit juices, TSB and distilled water. The spiked fruit juice samples were filtered through a mixed cellulose Metricel^TM filter. Spectra of the bacteria on these filters were collected using a ZnSe flat plate-ATR accessory on the FT-IR using 256 scans and 4 cm^-1 resolution. Spectra of E. coli O157:H7 and E. coli K12 in juices was analyzed using TQ analyst program. Discriminant analysis (DA) was applied to the amide II (1589-1493 cm ^-1) region and Mahalanobis distances (MD) were measured to quantify the spectral differences between the strains. DA was able to successfully classify and differentiate E. coli 0157:H7 from E. coli K12 against the background juice matrix at a performance index of 89% without any misclassifications. This approach could be expanded to reduce time for detection of bacteria in fruit juices.

Session 33, Food Microbiology: General
9:00 AM - 12:00 PM, Monday AM Room 395

2005 IFT Annual Meeting, July 15-20 - New Orleans, Louisiana