Detection of microbial biofilms on food processing surfaces: hyperspectral fluorescence imaging study

Abstract

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 <i>E. coli</i> O157:H7 and <i>Salmonella</i> cells were grown in low strength M9 minimal medium on various surfaces at 22 &plusmn; 2 &deg;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 <i>E. coli</i> O157:H7 and <i>Salmonella</i> 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.