35-6

L. M. GOELLER, Food Science Department, North Carolina State University, Schaub Hall, Raleigh, NC 27695 and T. C. Lanier.

Intact meats, particularly fish muscle, often suffer substantial losses in quality during frozen storage, resulting in water weepage from the thawed muscle and a concurrent toughening and dryness upon cooking. Much of this loss in quality can be attributed to denaturation of the myofibrillar proteins in the meat. Cryoprotection of intact fish muscle was previously demonstrated in our laboratory. The process must, however, be optimized to insure its feasibility in commercial practice.

The objective was to explore effects of vacuum and solute concentration on infusion rates of intact fish muscle by sorbitol.

Pieces of trout were infused by immersion in either 60% or 45% sorbitol solution using 5 vacuum treatments and 5 treatment times. Water/weight loss and sorbitol uptake were measured.

Vacuum did not have a consistent effect on sorbitol uptake. Sorbitol uptake and water loss rates were greater at the higher sorbitol concentration; however, uptake of sorbitol occurred mainly during the first 7.5 min. This indicated that a boundary layer formed at the surface of the meat, which impeded further uptake of solute, likely due to osmotic desiccation of the sample surface. Thus a second study was conducted at lower sorbitol concentrations (20% and 30%) using 2 vacuum treatments and the same 5 time intervals. Vacuum again did not have a significant effect on sorbitol uptake rate. Sorbitol uptake rate was more constant over the 30 min infusion period, achieving the desired 4-5% uptake level required for adequate cryoprotection only with the 30% solution, but water/weight loss rates were less using the 20% solution. Further study demonstrated that injection of 60% sorbitol solution or 30 min immersion infusion with 25% sorbitol achieved adequate cryoprotection. However, injection is a much faster process and would offset weight losses, which occur during immersion infusion due to osmotic drying.