Ellipsometry across isolated muscle fibres indicates a refractive contribution to paleness in pork

Abstract

Muscle fibres isolated from pork were mounted in a microscope chamber and pH was controlled with 0.2 M phosphate buffer. Optical path differences between ordinary and extraordinary rays were measured by ellipsometry while a scanning stage moved the fibre across the optical axis of the microscope. The depth of fibre in the optical axis was estimated from the lateral diameter of fibres. Path differences increased as fibre depth increased. Static ellipsometry of unmounted fibre fragments showed maximum path differences at pH 5.5 were higher than at pH 7.0, but variance was high and the difference was not significant (64.4±15.1 nm at pH 5.5 versus 58.9±15.2 nm at pH 7.0, P>0.05, n=40). However, the mean depth of fibre fragments at pH 5.5 was less than at pH 7.0 (53.9±15.1 μm at pH 5.5 versus 70.6±16.1 μm at pH 7.0, P<0.005, n=40). Thus, path differences per micrometre of fibre depth were greater at pH 5.5 than at pH 7.0 (1.25±0.37 nm −1 μm at pH 5.5 versus 0.87±0.31 nm −1 μm at pH 7.0, P<0.0005, n=40). As pH decreases, therefore, muscle fibre diameter decreases while birefringence increases. Refraction through muscle fibres may contribute to pork paleness.