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.