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We used a portable hyperspectral fluorescence imaging system to evaluate biofilm formations on four types of food
processing surface materials including stainless steel, polypropylene used for cutting boards, and household counter top
materials such as formica and granite. The objective of this investigation was to determine a minimal number of spectral
bands suitable to differentiate microbial biofilm formation from the four background materials typically used during
food processing. Ultimately, the resultant spectral information will be used in development of handheld portable
imaging devices that can be used as visual aid tools for sanitation and safety inspection (microbial contamination) of the
food processing surfaces. Pathogenic E. coli O157:H7 and Salmonella cells were grown in low strength M9 minimal
medium on various surfaces at 22 ± 2 °C for 2 days for biofilm formation. Biofilm autofluorescence under UV
excitation (320 to 400 nm) obtained by hyperspectral fluorescence imaging system showed broad emissions in the blue-green
regions of the spectrum with emission maxima at approximately 480 nm for both E. coli O157:H7 and Salmonella
biofilms. Fluorescence images at 480 nm revealed that for background materials with near-uniform fluorescence
responses such as stainless steel and formica cutting board, regardless of the background intensity, biofilm formation can
be distinguished. This suggested that a broad spectral band in the blue-green regions can be used for handheld imaging
devices for sanitation inspection of stainless, cutting board, and formica surfaces. The non-uniform fluorescence
responses of granite make distinctions between biofilm and background difficult. To further investigate potential
detection of the biofilm formations on granite surfaces with multispectral approaches, principal component analysis
(PCA) was performed using the hyperspectral fluorescence image data. The resultant PCA score images revealed
distinct contrast between biofilms and granite surfaces. This investigation demonstrated that biofilm formations on food
processing surfaces, even for background materials with heterogeneous fluorescence responses, can be
detected. Furthermore, a multispectral approach in developing handheld inspection devices may be needed to inspect
surface materials that exhibit non-uniform fluorescence.
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