Use chitosan as protein stabilizer for fish during frozen storage.

Protecting proteins is a primary concern when attempting to maintain quality during the freezing and frozen storage of fish. Currently, a 4%-sucrose/5%-sorbitol mixture is used in conjunction with phosphate as the industry standard.

In order to improve quality, new alternatives, which prevent protein denaturation, are continually being explored. The goal of scientists at Oregon State University was to measure the effects of chitosan as a replacement for phosphate. They wanted to see what effects chitosan had on the functional and biochemical properties of fish proteins during their frozen storage, and compare those results to a commercial control and screw-pressed meat. Their efforts indicate that chitosan may be a suitable phosphate replacement that can stabilize fish proteins during the product's frozen storage.

Researchers prepared four samples: a screw-pressed (SP) product, a commercial control with 0.3% STP, a 0.3% chitosan (T1) mix and a 1% chitosan (T2) mixture. Raw surimi was mixed with the respective ingredients at 5 C and packed in approximately 500-g portions. Then the samples were vacuum-packaged and frozen at -18 C, except the 0 month samples, which were stored at 5 C until they were tested.

Investigators tested the samples at 0, 1, 4, 8, 12 months of frozen storage to evaluate changes in salt extractable protein, turbidity, water retention ability, gelation properties, pH and color. For evaluating the gel, the samples were prepared with 2% salt and 1% BPP. They were adjusted to a 78% moisture content using ice and water. They were then cooked in stainless steel tubes at 95 C for 15 minutes.

The texture values of T1 after four months of frozen storage were equal to or better than those of the control. In addition, the T2 samples yielded salt extractable proteins greater than the control, supporting the role of chitosan as a stabilizer of proteins during frozen storage.

The color values of T1 and T2 were also comparable to the control, and the water retention ability of the chitosan samples (T1 and T2) was greater than or equal to that of the control after four months of frozen storage.

Further information. Jae Park, Department of Food Science and Technology, Oregon State University, Seafood Research Laboratory, 2001 Marine Dr., Room 253, Astoria, OR 97103; phone: [phone]; fax: [phone]; email: [e-mail].