Relationship between pork muscle fiber diameter and optical transmittance measured by scanning microphotometry

Abstract

Muscle fibers (n = 50) were isolated from pork psoas minor muscles and mounted in 0.2 M phosphate buffer at pH 5.5 or 7.0. A microscope scanning stage and photometer were used to measure transmittance (T) in relation to fiber diameter, anticipating attenuation of T with increasing diameter. However, T across fibers was often asymmetrical, showing fibers retained flattened sides after being released from bulk meat. A lateral measurement of fiber diameter (89.76 ± 17.07 μm at pH 5.5 and 97.43 ± 20.04 μm at pH 7.0, P > 0.05) was compared with minimum T at any point across a fiber. No T attenuation was detected at pH 7.0 (r = 0.07). At pH 5.5, instead of attenuation, the relationship of T with diameter was positive (r = 0.44, P < 0.05), possibly from differences in myofibrillar composition between small and large diameter fibers (fibrillenstruktur versus felderstruktur). However, attenuation at pH 5.5 was greater than at pH 7.0 (2.76 ± 1.19 vs. 1.42 ± 0.65 ΔT mm-1, respectively, P < 0.001) and was strongly related to wavelength (r = 0.97, P < 0.001). It was concluded fiber shape and fiber-type composition may affect optical properties of bulk meat and myofibrillar refraction may contribute to post-mortem development of normal paleness in pork.