Multispektrale, Diodenlaser-basierte Raman-Untersuchungen zur In-situ-Analytik ausgewählter Fleischsorten

This thesis aims to demonstrate the suitability of in situ Raman spectroscopy for the detection of microbial spoilage of meat and the non-invasive discrimination of selected animal species. For that purpose, an innovative portable prototype measurement system for Raman spectroscopic in situ investigations of meat was realized. All components of the system, including microsystem diode laser, optical elements, and a miniature spectrometer, were specially tailored and optimized for meat analyses. Extensive studies with pork meat were able to verify Raman spectroscopy as efficient method for the non-invasive spoilage detection. Applying statistical data analyses, a quantification of the microbial contamination with respect to the relevant limit of 10 cfu/cm could be achieved. Here, the verification of the spoilage status is based on the signal to background ratio of the spectra. While the Raman spectroscopic signature reveals changes in protein bands, the onset of a fluorescence emission caused by porphyrins becomes evident around 10 days after slaughter. Hence, in contrast to costly, labor-intensive, and time-consuming laboratory analyses, for the first time exceeding of the critical microbial load can be gathered within a few seconds and in situ using the portable Raman system. A multispectral excitation concept demonstrated the applicability of 785 nm and 671 nm as excitation wavelengths, whereas 488 nm is well suited for the sensitive detection of carotenoids. As target wavelength for the portable system, 671 nm was identified as being particularly advantageous. Here, measurement times of only 1 s were sufficient to enable for a classification of the meat samples and thus making on-line investigations feasible. By means of selected packaging types, the measurement process could be verified as suitable technique for investigations even through the packaging foil. Compared to other detection methods for microbial spoilage, this option is a crucial advantage and qualifies the system for future usage by food inspectors. Furthermore, the transferability to beef as well as chicken and turkey meat could be experimentally verified and underlines the universal appropriateness of the applied detection concept. Based on the previous results, two novel miniaturized prototype measurement heads each comprising two slightly shifted emission wavelengths (671.0 nm and 671.6 nm or 782.65 nm and 783.15 nm) for shifted excitation Raman difference spectroscopy (SERDS) were developed. Using these devices, for the first time a non-invasive differentiation of meat and meat juice from pork, cow, chicken, and turkey could be realized using principal components analysis and applying integration times of 10 s only. Here, the content of the muscle pigment myoglobin as well as differences in the protein composition were identified as distinctive features. These findings demonstrate the large potential of SERDS as rapid test method for the in situ identification of selected animal species.