This paper reported the development of hyperspectral fluorescence imaging system using ultraviolet-A excitation (320-400 nm) for detection of bovine fecal contaminants on the abaxial and adaxial surfaces of romaine lettuce and baby
spinach leaves. Six spots of fecal contamination were applied to each of 40 lettuce and 40 spinach leaves. In this study,
the wavebands at 666 nm and 680 nm were selected by the correlation analysis. The two-band ratio, 666 nm / 680 nm, of
fluorescence intensity was used to differentiate the contaminated spots from uncontaminated leaf area. The proposed
method could accurately detect all of the contaminated spots.
Organic residues on equipment surfaces in poultry processing plants can generate cross contamination and increase the
risk of unsafe food for consumers. This research was aimed to investigate the potential of LED-induced fluorescence
imaging technique for rapid inspection of organic residues on poultry processing equipment surfaces. High-power blue
LEDs with a spectral output at 410 nm were used as the excitation source for a line-scanning hyperspectral imaging
system. Common chicken residue samples including fat, blood, and feces from ceca, colon, duodenum, and small
intestine were prepared on stainless steel sheets. Fluorescence emission images were acquired from 120 samples (20 for
each type of residue) in the wavelength range of 500-700 nm. LED-induced fluorescence characteristics of the tested
samples were determined. PCA (principal component analysis) was performed to analyze fluorescence spectral data.
Two SIMCA (soft independent modeling of class analogy) models were developed to differentiate organic residues and
stainless steel samples. Classification accuracies using 2-class ('stainless steel' and 'organic residue') and 4-class
('stainless steel', 'fat', 'blood', and 'feces') SIMCA models were 100% and 97.5%, respectively. An optimal single-band
and a band-pair that are promising for rapid residue detection were identified by correlation analysis. The single-band
approach using the selected wavelength of 666 nm could generate false negative errors for chicken blood inspection.
Two-band ratio images using 503 and 666 nm (F503/F666) have great potential for detecting various chicken residues on stainless steel surfaces. This wavelength pair can be adopted for developing a LED-based hand-held fluorescence imaging device for inspecting poultry processing equipment surfaces.
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.
A rapid nondestructive technology is needed to detect bacterial contamination on the surfaces of food processing
equipment to reduce public health risks. A portable hyperspectral fluorescence imaging system was used to evaluate
potential detection of microbial biofilm on stainless steel typically used in the manufacture of food processing
equipment. Stainless steel coupons were immersed in bacterium cultures, such as E. coli, Pseudomonas pertucinogena,
Erwinia chrysanthemi, and Listeria innocula. Following a 1-week exposure, biofilm formations were assessed using
fluorescence imaging. In addition, the effects on biofilm formation from both tryptic soy broth (TSB) and M9 medium
with casamino acids (M9C) were examined. TSB grown cells enhance biofilm production compared with M9C-grown
cells. Hyperspectral fluorescence images of the biofilm samples, in response to ultraviolet-A (320 to 400 nm) excitation,
were acquired from approximately 416 to 700 nm. Visual evaluation of individual images at emission peak wavelengths
in the blue revealed the most contrast between biofilms and stainless steel coupons. Two-band ratios compared with the
single-band images increased the contrast between the biofilm forming area and stainless steel coupon surfaces. The
444/588 nm ratio images exhibited the greatest contrast between the biofilm formations and stainless coupon surfaces.
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