Proceedings of the Third World Fisheries Congress: Feeding the World with Fish in the Next Millenium—The Balance between Production and Environment
Texturization of Low-Value Fish Protein Using a Twin-Screw Extruder
Junrong Liu, Yongji Lu, Yuming Ye, Qiukuan Wang
Food extrusion has been practiced for more than 60 years. An extruder is considered a high-temperature short-time (HTST) bioreactor—operating at high temperatures with short residence times under high pressures and high shear forces—that transforms a variety of raw ingredients into modified intermediate or finished products (Harper 1983). By extrusion cooking, it is possible to produce products with attractive textures such as textured products with meat structure. The impetus for these developments has come from modern food processing needs for continuous processes with high throughput, energy efficiency, modified textural and flavor properties of foods, control of the thermal effects on food constituents, and new and unique food products.
The principal difference between twin- and single-screw extruders is that the twin-screw extruder eliminates or minimizes pressure and leakage flow by virtue of the direction of screw rotation, screw shape, and so on (Akinori 1989). This characteristic suggests that the twin-screw extruder may be more suitable for handling high-moisture materials. It provides new ways to process wet marine material such as fish meat, with improved texture and the possibility of taste modification.
Many reports have been published about animal meat texturization using a twin-screw extruder (Kristensen et al.1983; Aoki et al.1989; Kimura 1992). Extrusion of protein-rich materials is used to create various “fabricated” foods, most commonly meat analogues or extenders. Kristensen et al. (1983) conclude that extrusion processes can be used with great success for upgrading underutilized animal by-products.
The use of the marine catch is far from optimal; only about 70% of the total landings are intended for human consumption in different forms. In the fish industry, tremendous amounts of underused edible by-products are available. On the other hand, because of the depletion of many valuable resources traditionally used for producing popular fish products, fish protein from less valuable but abundant species is important to alleviate a protein shortage in human nutrition. The increased demand for fish products and the reduced catch of commercially important species has led to adulteration or substitution of these species with cheaper species. Fatty pelagic species such as herrings and sardines (Clupeidae) and mackerels (Scombridae) are a large resource. Because of their small size, large number of bones, dark color, or undesirable flavor and texture, these species are rarely used in popular fish products.
To produce consumer value-added products with higher acceptability is important to the use of trash fish. Experience has proven that it must be delivered in forms that fall within the organoleptic limits established by traditional human eating habits. So, by converting fish into protein food ingredients, the products should have a functional value in the food systems already familiar to a populace.
A fibrously texturized product, a kind of value-added product, was obtained from minced fish and soybean protein isolate (SPI) by extrusion cooking with a twin-screw extruder. The extrudates have a spongelike structure and the chewiness properties of meat. The extrudates are then further dried. When rehydrated, the final products have a meat-like texture and can be used as a “fabricated” meat or meat extender.