Sarcomere is the fundamental functional unit in skeletal muscle for force generation. In addition, sarcomere
structure is also an important factor that affects the eating quality of muscle food, the meat. The sarcomere
structure is altered significantly during rigor mortis, which is the critical stage involved in transforming muscle
to meat. In this paper, we investigated optical scattering changes during the rigor process in
Sternomandibularis muscles. The measured optical scattering parameters were analyzed along with the
simultaneously measured passive tension, pH value, and histology analysis. We found that the temporal
changes of optical scattering, passive tension, pH value and fiber microstructures were closely correlated
during the rigor process. These results suggested that sarcomere structure changes during rigor mortis can
be monitored and characterized by optical scattering, which may find practical applications in predicting meat quality.
We recently found that optical scattering coefficients of beef muscle can be used as a predictor for beef
tenderness. However, it is still not clear what specific muscle properties are responsible for optical scattering.
As an effort to answer these questions, we conducted several controlled experiments in which we studied the
changes of scattering coefficient with muscle sarcomere length and ageing time. The optical scattering
coefficient of beef muscles were measured based on a diffusive fitting of spatially resolved reflectance
measurements. Samples with different sarcomere lengths were obtained by proper carcass hanging
strategies. Our results indicated that muscle scattering coefficient increased with ageing time and sarcomere
length. These experimental observations can be qualitatively explained based on previous research on single
muscle scattering. This study suggests that muscle structural properties have significant impact on muscle
optical scattering coefficients.
Our recent studies indicated that the optical scattering has the ability to characterize the micro structures in
beef muscles. In this study, optical scattering spectra of beef semimembranosus and longissimus muscle
samples were measured at different cooking temperatures along with the corresponding Warner-Bratzler
shear force values. Overall, scattering coefficients increased first and then decreased. The increase was likely
due to the denaturation of myosin and the thermal-stable collagen cross links depending on the temperature
ranges; while the decrease was attributed to the gelatinization of thermal-labile collagen cross links. The
collagen content and the relative proportionality of the thermal-stable and the thermal-labile collagen cross
links could affect the relative changes of the scattering coefficients at different temperatures. Our results
indicated that the optical scattering can indeed reflect the states of the micro structures in beef muscles and
have the potential to be used as an indicator for beef quality prediction.
Normal biomechanical and physiological functions of striated muscles are facilitated by the repeating sarcomere units. Light scattering technique has been used in studying single extracted muscle fibers. However, few studies, if any, have been conducted to investigate the possibility of using optical detection to examine sarcomere structure changes in whole muscles. We conducted a series of experiments to demonstrate that optical scattering properties measured in whole muscle are related to changes in sarcomere structure. These results suggest that photon migration technique has a potential for characterizing in vivo tissue ultrastructure changes in whole muscle.
An objective and reliable method for meat quality measurement will benefit both consumers and meat industry. Among various techniques, optical methods have the advantage of being fast, flexible, inexpensive and nondestructive, which are important characteristics for online quality control. Although there have been great progress in this area, many results are inconsistent and controversial because of the lack of fundamental understanding of in light-meat interactions. Optical measurements on meat tissues are affected by both meat scattering and absorption properties. In the project, a method based on diffuse approximation solution of light transport in tissue was used to derive meat scattering and absorption coefficients. Differentiating muscle scattering properties from absorption properties are important for muscle characterization because they represent distinctly different aspects of muscle physical and chemical components. Our preliminary results showed that scattering coefficients can detect variations in beef steak tenderness. This new technique is promising to be used as an indicator for beef tenderness. However, a more extensive study with larger sample population will be necessary to fully test the capability of using optical scattering for beef tenderness characterization.