Linda Benedict, Prinyawiwatkul, Witoon | 5/28/2009 1:44:46 AM
Most catfish is processed into fresh or frozen fillets and whole-dressed fish. Other products include steaks, nuggets and value-added products, which accounted for 21 percent of the total products sold in 1998. The dress-out yield of catfish, when processed as fillets, is about 45 percent, generating about 55 percent by products. Up to75 percent of usable minced meat can be recovered from catfish frames. Catfish processors have increasingly shown interest in converting by products or processing waste into edible value- added food products. Several researchers have investigated the recovery of minced meat from filleted catfish frames using a mechanical meat-bone separator. This minced meat can be further processed into surimi. Surimi has little or no flavor of the original fish and therefore can be used as an intermediate raw material for various seafood-based products.
Modified surimi processing
The basic surimi manufacturing process involves washing the mince, draining to remove excessive water, straining or refining to remove remaining skin or bones, screw-pressing to dewater, mixing the mince with cryoprotectants, packing and freezing. The estimated production cost for producing surimi from mince recovered from catfish frames using the standard commercial techniques is probably higher than that of commercial surimi made from Alaska pollock. The process to produce catfish surimi requires large volumes of water to remove blood, pigments, lipids and water-soluble proteins. Reducing the water required would lower the production cost and reduce the space required for wastewater treatment. Lower production costs would encourage catfish processors to further invest to extend the production line to include surimi.
Process modification to reduce production cost of catfish surimi is being investigated by researchers in the Department of Food Science. Two different processing techniques were applied for the washing step: (1) a traditional process—twice washing using 1 part mince to 3 parts ice-water and (2) a modified process—one washing using 1 part mince to 5 parts ice-water with 0.5 percent sodium bicarbonate. The yield (about 23 percent) of surimi products prepared from both processes was not significantly different. The modified process yielded surimi with significantly lower fat (0.02percent) and higher protein (15 percent), however, than the standard process. The modified process also resulted in a lower whiteness index and liquid expressible drip.
Our study suggested that water volume required for catfish surimi processing can be reduced. Furthermore, all significant potential human pathogens were reduced to a non-detectable level as a result of our controlled processes used during production of minced meat and surimi products.
Improving whiteness of catfish surimi
Another major concern of surimi quality is color. Surimi processed from catfish filleted frames has inferior whiteness (55) compared to commercial surimi, which normally has a whiteness value around 67. Appearance plays a critical role in food acceptance. Our interest was therefore to determine the feasibility of improving color whiteness of catfish surimi using titanium dioxide, a simple and economical approach. The surimi samples were thoroughly mixed with titanium dioxide and subsequently analyzed instrumentally and by consumers. Significant improvement of whiteness of surimi products over the control (no added titanium dioxide) was observed at 0.1 percent titanium dioxide. Whiteness of surimi increased with increased percentage of titanium dioxide. Adding more than 0.7 percent titanium dioxide did not significantly increase whiteness. Consumers perceived differences in whiteness when titanium dioxide was added at 0.1 percent. Acceptability of surimi was increased over the control sample when at least 0.5 percent titanium dioxide was added.
Value-added formed catfish products
Interest in developing formed catfish products from unwashed mince recovered from filleted frames has increased. Because of its poor functionality, unwashed mince may not yield formed products with desirable texture. Food-grade binders have been used to enhance the textural quality of several restructured muscle food formulations. Our work indicated that whey protein isolate, sodium alginate and waxy rice starch can serve as good binders. Restructured fish products are normally prepared by chopping surimi with whole fish muscle, salt and binders. At the Department of Food Science, we have investigated the feasibility of using either unwashed frame mince or a mixture of unwashed mince and surimi as a major ingredient in restructured catfish products. Several new formed catfish products, such as nibblets, fingers, cracker and chips, have been developed and are being tested. In the summer of 1999, we conducted a consumer acceptance test for our novel nibblet product. This product was made of minced meat and surimi, rice starch, salt, white pepper, garlic powder, parsley and sweet corn. A total of 123 consumers participated in this study. More than 60 percent of there sponses indicated that consumers liked the product. About 83 percent indicated that the product was acceptable, and 70 percent would buy the product. Of those who would buy, 76 percent would be willing to pay the same price as a similar product, and 7 percent would be willing to pay more.
Impact on the catfish industry
As demand for surimi continues to grow and a global natural fishery catch declines, by products from catfish filleting may serve as an alternative for the surimi production. Potential exists for the development of both catfish mince-based and surimi-based products, which may, inturn, form potential new market niches that will be beneficial to the catfish industry.
Witoon Prinyawiwatkul, Assistant Professor; Voranuch Suvanich, Postdoctoral Research Associate; and Wanda J. Lyon, Assistant Professor, all with the Department of Food Science, LSU Agricultural Center, Baton Rouge, La.
(This article was published in the fall 1999 issue of Louisiana Agriculture.)