Refractometry of pork muscle and beef connective and adipose tissue

Bulk refractive index (RI) was measured with an Abbe refractometer using a red laser for transmittance (T) and a green laser for reflectance. The critical angle, although obscured by scattering, was detected subjectively at the red-green boundary. The refractometer also was operated under computer control, detecting RI photometrically. Pork longissimus thoracis (n=20) had higher RI than biceps femoris (1.357±0.004 versus 1.352±0.005, respectively, P<0.001). Longissimus thoracis also had lower Japanese pork colour scores (JPCS) than biceps femoris (2.92±0.37 versus 3.87±0.48, respectively, P<0.001). In pooled samples (n=40), RI was correlated with JPCS, r=-0.55, P<0.001. RI of bovine tendon (n=10) was higher than for adipose tissue (1.415±0.009 versus 1.343±0.001, P<0.001). Refraction may contribute to the inverse relationship between meat pH and paleness, and may affect signals from fibre-optic meat probes.