Submitted to: Journal of Food Engineering
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/6/2010
Publication Date: 4/19/2010
Citation: Jun, W., Kim, M.S., Cho, B., Millner, P.D., Chao, K., Chan, D.E. 2010. Microbial biofilm detection on food contact surfaces by macro-scale fluorescence imaging. Journal of Food Engineering. 99(3):314-322. Interpretive Summary: Adequate cleaning and disinfection of food processing equipment are essential to maintaining sanitary and safe food processing operations. Food residues on inadequately cleaned equipment surfaces can encourage microorganisms, such as pathogenic E. coli or Salmonella, to form biofilms (a mass of bacterial growth) on surfaces. Such biofilms can lead to cross-contamination of food products that come into contact with the contaminated surfaces and may potentially cause foodborne illnesses. Hyperspectral fluorescence imaging was used to analyze E. coli and Salmonella biofilms on four common industry/household surface materials used to process or handle food: stainless steel, high density polyethylene (HDPE, used for cutting boards), Formica (plastic laminate) and granite countertop materials. The spectral fluorescence characteristics of the biofilms and the surface materials were analyzed to select wavebands useful for detection and classification of bacterial biofilms on equipment surfaces. Spectral fluorescence methods in this study were found capable of effectively classifying E. coli and Salmonella biofilms on stainless steel, HDPE, and granite; biofilm detection on the Formica surface was found to be more difficult. The spectral fluorescence information for the biofilms and surface materials and the image analysis methods in this study can be incorporated into developing portable handheld imaging devices for sanitation inspection of food processing surfaces. This research is of interest to food technologists and the food processing industry.
Technical Abstract: Hyperspectral fluorescence imaging methods were utilized to evaluate the potential of multispectral fluorescence methods for detection of pathogenic biofilm formations on four types of food contact surface materials: stainless steel, high density polyethylene (HDPE) commonly used for cutting boards, and plastic laminate (Formica) and polished granite countertop materials. The main objective of this study was to determine a minimal number of spectral fluorescence bands suitable for detecting and classifying microbial biofilms on surfaces commonly used to process and handle food. Sample surface materials were spot-inoculated (100 µl on approximately 1-cm diameter areas) with pathogenic E. coli O157:H7 and Salmonella and then stored at room temperature for 3 days to allow for biofilm growth. Following biofilm formation, hyperspectral fluorescence images of the sample surfaces were acquired using ultraviolet-A (UV-A) excitation (320 to 400 nm). The biofilms emitted fluorescence predominantly in blue to green wavelengths with emission maxima at approximately 480 nm for both E. coli O157:H7 and Salmonella. Results indicated that a single green band (559 nm) can provide a means to detect biofilm on stainless steel. On HDPE and granite, two-band ratio algorithms provided better classification than single-band images did for both E. coli and Salmonella biofilm contamination spots. Fluorescence imaging techniques successfully detected 95 percent of the biofilms on stainless steel, HDPE, and granite. On Formica, too many false positives were present to accurately determine an effective biofilm detection rate. This may have been due to the heterogeneous background fluorescence response and low cell population density (approximately 4.3 to 6.4 log CFU cm-2) that was observed for the Formica compared to the other surface materials. The spectral fluorescence information for the biofilms and surface materials and the image analysis methods in this study can be incorporated into developing portable handheld imaging devices for sanitation inspection of food processing surfaces.