Relationships between the back-scatter of polarised light and the fibre-optic detection of connective tissue fluorescence in beef

The back-scatter of light (400-800 nm) from bovine m longissimus lumborum (n = 47) was measured with a fibre-optic probe fitted with crossed polarisers to exclude Fresnel reflectance. Unlike normal fibre-optic spectra (which may be relatively flat), back-scatter was approximately proportional to wavelength, being low at 400 nm and high at 800 nm. The shape of the spectrum was modified by myoglobin absorbance, with a Soret minimum at 430 nm. Connective tissue fluorescence (365 nm excitation, 400-550 nm emission) was measured through a single optical fibre moving down the longitudinal axis of the muscle. Back-scatter at 430 nm was correlated positively with minimum fluorescence (r = 0.73, P < 0.001), the area under the fluorescence signal cm(-1) (r = 0.81, P < 0.001) and fluorescence peaks cm(-1) (r = 0.46, P < 0.005). Back-scatter at 800 nm was correlated weakly and negatively with minimum fluorescence (r = -0.28, P < 0.05) and peaks cm(-1) (r = -0.26, P < 0.05). Thus, in the probe detection of connective tissue fluorescence in meat, errors caused by differences in myoglobin concentration may exceed those caused by differences in pH-related light scattering.