14A-34

J. W. BELL¹, B. E. Farkas, and S. A. Hale. (1) Food Science, North Carolina State University, Schuab Hall, Box 7624, Raleigh, NC 27695

JUSTIFICATION: The United States canned tuna industry produced over one billion cans of light meat tuna in 1997. Unlike most canned foods which are regulated by drained weight, canned tuna fill weight is determined by pressed weight testing. This procedure involves applying high pressure to the retorted tuna meat to express liquid. The compressed tuna cake mass is then measured for fill weight compliance. This press test has been employed without fundamental understanding of liquid expression from retorted tuna muscle cakes.

OBJECTIVE: The objective of this work was to study the fundamental properties of liquid mass transfer during liquid expression of canned skipjack tuna muscle cakes.

METHOD: A vertically aligned press cylinder with a perforated bottom was designed and constructed to measure force, deformation, and mass data during controlled expression of canned tuna muscle. Post-expression measurements of liquid viscosity, and liquid and cake mass and moisture content were performed.

RESULTS: The expression of liquid from tuna muscle cakes can be described by the d'Arcy equation. Expressed liquid flow rates are dependent on changes in compression distance and pressure over time. Adjusting tuna processing parameters achieved differences in liquid viscosity and cake porosity of canned samples, and these changes affected mass transfer, cake rheology, and water holding properties.

SIGNIFICANCE: These results suggest that varying tuna processing parameters can affect tuna muscle expression results. Controlling pre-cook time, piece size, and other processing variables can affect the physical properties involved in porous media flow. Understanding the effects of these properties and the ability to mathematically model tuna cake expression can facilitate process optimization and balance the canned yield and product quality improvement goals of the canned tuna industry.