Kinetics of migration of colloidal particles in meat muscles in the absence and presence of a proteolytic enzyme to simulate non-motile bacteria penetration

- Particles and defined enzyme activity can simulate behavior of non-motile bacteria.
- Particles migrated from the injection zone into the inner structure of meat.
- Particles migrated preferentially in intermediate spaces between muscle fibers.
- Cluster-like and more widespread migration of particles took place with protease.
- Apparent diffusion coefficients increased with addition of protease.

In this study, migration rate and spatial distribution of colloidal particles with and without proteolytic enzymes were studied after injection in pork loin muscle cubes for 5 days at 25 °C to simulate behavior of non-motile bacteria. Samples were monitored daily by light microscopy and confocal laser scanning microscopy and particle distribution and movement analyzed by image analysis (MATLAB®). The extent of proteolytic activity was assessed by determining the tyrosine content in muscle tissue. Results showed that particles diffused from the injection hot spot into the inner structure of the meat (1.35 ± 0.99 × 10− 12 to 2.39 ± 2.02 × 10− 12 m2/s). Upon addition of protease, the migration rate increased, i.e. the particle distribution became more widespread due to proteolysis of meat proteins reducing resistance to mass transfer. Results indicate that particles are able to diffuse into the densely packed fiber structure of meat muscles, which is contrary to the long held belief that such penetration may not occur in the absence of extensive proteolysis or mechanical damage of tissue.