A portable 671 nm Raman sensor system for rapid meat spoilage identification

Abstract This paper presents a portable Raman sensor system based on a miniaturized optical bench with integrated 671 nm microsystem diode laser as excitation light source for the rapid in situ detection of meat spoilage. The system comprises three main components. A handheld measurement head with a dimension of 210 mm × 240 mm × 60 mm containing a laser driver electronics board, the Raman optical bench, and a battery pack as power supply serves for excitation as well as collection of the Raman signals in backscattering geometry. The signal detection is realized by a custom-designed miniature spectrometer with an optical resolution of 8 cm −1 and a dimension of 200 mm × 190 mm × 70 mm which is fiber-optically connected to the measurement head. To control the spectrometer as well as for data storage a netbook is applied. To point out the ability of the sensor system for the rapid identification of meat spoilage porcine musculus longissimus dorsi (LD) and musculus semimembranosus (SM) were used as test samples. Stored refrigerated at 5 °C the meat cuts were investigated in time-dependent measurement series up to 3 weeks after slaughter. Meat Raman spectra with an integration time of 10 s can be detected with an excitation laser power of 100 mW at the sample. The spectral changes of the Raman data set during storage were analyzed by principal components analysis. Specific periods of age could be discriminated in the Raman spectra which correlate very well with bacterial growth kinetics determined by microbial reference analyses. Thus, fresh meat with low bacterial load can be identified and a discrimination of spoiled samples exceeding the threshold of 10 6  cfu/cm 2 around day 7 post-mortem for both examined meat cuts was possible.