Measurement of the gristle content in beef by macroscopic ultraviolet fluorimetry

Ultraviolet light (365 nm) was directed at an angle of 45 degrees onto meat samples in a circular aperture (3 cm diameter). Fluorescence emissions were measured with a monochromator and a photomultiplier tube. Intact tendons and elastic ligaments had a strong fluorescence emission peak around 440 to 450 nm and only weak fluorescence around 510 nm. Tissues such as lean meat and adipose tissue that contain a matrix of reticular fibers (Type III collagen) had very low fluorescence around 440 to 450 nm so that their peak emittance was the weak fluorescence peak at 510 nm. The 510/440 nm ratio of fluorescence emissions was measured in comminuted meat samples containing varying mixtures of lean meat and gristle and varying mixtures of muscles with a high and low gristle content. The 510/440 nm ratio was correlated with the ratio of lean meat/gristle (r = .96, P less than .005). The 510/440 nm ratio was correlated with the ratio of longissimus/shank meat (two trials; r = .93, P less than .01; and r = .94, P less than .005). Results were only slightly changed when samples had dry surfaces or when samples were mixed with adipose particles. The relationship between the area of gristle in the samples and the 510/440 nm ratio was curvilinear with the greatest sensitivity to the fewest gristle fragments.