Witoon Prinyawiwatkul, Voranuch Suvanich, R. Wes Harrison, Joan M. King, Subramaniam Sathivel, Karoline Pacheco, Sandeep Kumar Rout, Kandasamy Nadarajah and Sirisha Sonti

Because of declining natural fishery resources and increasing consumer demand for fishery and aquacultural products, it is no longer practical to discard undersized crawfish and byproducts and wastes from crawfish and catfish processing plants, especially when a significant amount of valuable raw materials can be recovered and used to produce value-added new products and functional ingredients. The magnitude of this resource as a raw material for value-added products suggests a strong economic potential with major impact on the entire catfish and crawfish industries.

Crawfish
Louisiana is the world’s largest producer of crawfish with an average annual harvest exceeding 100 million pounds. Along with edible crawfish tailmeat, about 85 million pounds of peeling waste is generated in Louisiana annually. The peeling waste is used as animal feed with low economic value, although it is an inexpensive source of the valuable orange-red pigment, asthaxanthin, and the biopolymer, chitosan.

Before processing, crawfish are typically sorted into three grades: large/export, medium/restaurant and small/manual processing. The grading process results in a notable volume of undersized crawfish too small for manual peeling—more than 20 million pounds in some years. Lack of satisfactory markets for overabundant undersized crawfish can be economically devastating for processors and remains one of the problems facing the Louisiana crawfish industry. LSU AgCenter researchers have demonstrated that by using a meat-bone separator located at the Food Processing and Technology Laboratory, they can mechanically recover minced meat from cooked, undersized crawfish. With this recovered crawfish mince, formed seafood products can be created.

Because availability of crawfish is highly seasonal, thorough understanding of storage conditions, shelf-life quality and microbial safety of mince recovered from undersized crawfish are critical for effective development of value-added seafood products safe for human consumption. Crawfish mince has 14.4 percent protein, 80.4 percent moisture, 2.1 percent fat and 1.3 percent ash. Even after six months of storage at minus 20 degrees C, the mince maintains an appealing orange-reddish color. Furthermore, this frozen mince resembles fresh mince, having no apparent offensive odor. LSU AgCenter studies show that formed seafood products made from crawfish mince, which required further heat treatment during cooking, were free of pathogens and safe for consumption. The shelf stability of crawfish frozen mince, which is up to six months without added preservatives, is attributed to its low fat content and the presence of the natural antioxidant, astaxanthin.

Consumer Survey
A survey was conducted with 1,600 seafood restaurants in Louisiana, Mississippi and Texas to evaluate desirable quality attributes of crawfish mince. Mince freshness was identified as the most critical attribute affecting end-product quality and purchase intent. Minced meat from cooked, undersized crawfish was successfully used as a base for several new formed seafood products such as nuggets, patties and sausages. These products were acceptable to consumers and more than 80 percent of the consumers participating in the tests indicated that they would purchase the products if commercially available. Flavor was most critical to overall acceptance and purchase intent of the crawfish mince-based products from the consumers’ point of view.

Chitosan
Crawfish shell waste is a good and inexpensive source of chitosan. Chitosan is a biopolymer having numerous food applications. Traditional chitosan production involves four steps: demineralization, deproteinization, decoloration and deacetylation. AgCenter researchers successfully simplified the process, which also reduced some chemical waste.

The fat-binding capacity of chitosan has made it a potential weight-reduction food supplement. We discovered that crawfish chitosan has more than 750 percent fat-binding capacity.

Chitosan is a natural antimicrobial and antifungal substance and may be used to produce an edible film coating. We are currently studying the filmogenic properties of crawfish chitosan. Coating whole or fresh-cut fruits and vegetables with chitosan film may prolong shelf life. The market demand for fresh-cut fruits and vegetables has undergone rapid expansion in recent years. We are investigating the effect of chitosan coating on shelf stability of fresh-cut apples. Our preliminary study indicated that the coated fresh-cut apples lasted at least one week without surface browning.

Catfish
Most catfish processed in the United States is sold as fresh or frozen fillets and whole-dressed fish. The yield from dressed-out catfish from traditional processing is only 45 percent, while offal (including catfish frames, viscera, skin and trimmings) derived from the filleting process, which often ends up in landfills or rendering plants, amounts to 55 percent of the total live catfish weight. Up to 75 percent of usable mince can be recovered from a catfish frame. The mince can be directly used in formed seafood products or further processed into surimi. Crude fat can be extracted from the viscera and head, purified and potentially used as seasoning oil or functional food supplement.

Surimi Production
Catfish processors have increasingly shown interest in converting byproduct or waste into edible value-added food products. At the LSU AgCenter, we successfully developed the process to recover minced meat from filleted catfish frames. The mince was furthered processed into surimi. Our surimi production process requires less wash-water volume than the traditional process, yet provides quality comparable to that of the commercial surimi products. 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. Reducing the costs would encourage catfish processors to further invest to extend the production line to include surimi. Catfish 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. Surimi produced from catfish frame mince has inferior whiteness compared to commercial surimi. Our studies show that significant improvement of whiteness of catfish surimi can be achieved with addition of 0.1 percent titanium dioxide. Consumer acceptability of catfish surimi is increased when at least 0.5 percent titanium dioxide is added.

Catfish frame mince and surimi, alone or in combination, were successfully used as major ingredients for various seafood-based products such as nibblets, fingers, chips and sausages. Product acceptability, opportunity and market potential for nibblets, fingers and seafood sausage were investigated. Flavor and texture were most critical to product acceptance. Since safety is critical to the success of any new products, we developed the generic model Hazard Analysis and Critical Control Point (HACCP) for raw frozen catfish mince, catfish surimi and derived value-added products.

As demand for surimi products continues to grow and a global natural fishery catch declines, byproducts from the catfish filleting operation may serve as an alternative for surimi production. Potential exists for the commercial-scale development of both catfish mince-based and surimi-based products, which may in turn form new market niches that will be beneficial to the catfish industry.

Catfish Viscera
There has been little interest to add value to catfish viscera, a processing waste. A whole viscera, which includes the liver, gallbladder, digestive tract (intestine and stomach) and storage fat, weighs about 10 percent of a live catfish. Our study indicated that catfish viscera contains about 30 percent to 35 percent fat. Docosahexaenoic and arachidonic acids in natural fish oil have been touted as helping maintain heart required wash-water would lower the production cost and reduce the space required for wastewater treatment. Lower production and vascular health in humans. We found that catfish viscera contain these two health-promoting fatty acids. Recovery, extraction and purification processes for catfish visceral oil were developed, and the oil quality characterized. Conventional oil refining is achieved through the following steps: degumming, neutralization, bleaching and deodorization. We discovered that chitosan (functional ingredient derived from crawfish shell waste) was an effective adsorbent for removing free fatty acids (causing offensive odor) from crude catfish oil. The use of chitosan may eliminate the neutralization step. Further research on proper process design and process optimization for a larger scale production of catfish oil is essential. A market feasibility study is also needed.

Economic Impact
The outlook for more innovative and effective processing technology for byproduct recovery is promising. With enforcement of pollution laws to protect the environment, catfish and crawfish processors have shown an increasing interest in using byproducts and processing wastes. This would minimize pollution problems and offset costs involved in disposal of processing byproducts and wastes and at the same time maximize the processors’ profits. In the long run, the use of byproducts and wastes from catfish and crawfish processing plants will not only enhance the competitiveness of the Louisiana catfish and crawfish industries, but also enhance the state’s economic development.

(This article was published in the fall 2002 issue of Louisiana Agriculture.)