The Surimi Process

A typical surimi process on a pilot-plant scale is shown in Figure 2. The fish is headed, gutted, and cleaned in a washing tank. The washed fish is then put through a belt-drum-type meat separator that separates the flesh from the bone and skin. The fillets processed by a high-speed filleter are often favored over headed and gutted fish for surimi of superior quality. The diameter of the drum perforations ranges from 4 to 7 mm and is selected in accordance with the size and freshness of the fish (7). For the production of high-quality surimi with limited washing, particularly in the case of on-board processing, the backbone is mechanically removed, or the fillet is used. Filleting is done mechanically using a filleting machine at a fast speed.

Basically, surimi is produced by repeatedly washing mechanically separated fish flesh with chilled water (10°C) until it becomes odorless and colorless or, technically, until most of the water-soluble proteins are removed. The water temperature does not need to be kept unnecessarily low. It should be determined by the type of fish (species), specifically the thermostability offish protein; for example, 10°C for Alaska pollock (a cold-water fish) and 15°C for red hake (Urophycis chuss, a temperate-water fish) (8). On the basis

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Figure 1. An old surimi and kamaboko making process; (1) fish harvest, (2) gutting and cleaning, (3) filleting, (4) mincing, (5) washing, (6) dewatering, (7) chopping, (8) stone grinding with salt and spices, (9) straining, (10) shaping of kamaboko, and (11) steaming of kamaboko. Source: Courtesy of Suzuhiro Kamaboko Kogyo Co., Ltd., Odawara, Japan.

Figure 1. An old surimi and kamaboko making process; (1) fish harvest, (2) gutting and cleaning, (3) filleting, (4) mincing, (5) washing, (6) dewatering, (7) chopping, (8) stone grinding with salt and spices, (9) straining, (10) shaping of kamaboko, and (11) steaming of kamaboko. Source: Courtesy of Suzuhiro Kamaboko Kogyo Co., Ltd., Odawara, Japan.

of the relationship between species and thermostability of actomyosin ATPase (9), it can be assumed that warm-water fish can tolerate a higher water temperature than cold-water fish without a reduction in protein functionality.

In a washing process, the number of washings, the volume of water, and the washing time will vary with the fish species, the initial condition of the fish (freshness), the type of washing unit, the ratio of water to meat weight, and the desired quality of surimi (10). Generally, in the shore plant process three washings are recommended at a 4:1 ratio of water to meat, while in the factory ship process two washings are done at two to three parts water to one part meat because of fresh water shortage. Based on 5 min for each washing and two to three washing cycles, 15 to 20 min for the entire leaching process is appropriate for a commercial surimi manufacturing operation.

In a commercial process, the washing is done continuously, with mechanical agitation in a series of washing tanks and a rotary screen rinser. During repeated washings with continuous agitation, much of the water-soluble proteins are removed, along with undesirable substances and enzymes, causing the level of actomyosin to increase. The level of functional actomyosin is a measure of the gel-forming ability of the surimi. This explains why surimi gives a more elastic texture than unwashed minced fish meat. For the last washing, a 0.1 to 0.3% NaCl solution is used to ease the removal of the water. The washing is followed by refining with the aid of a refiner that removes connective tissue, black skin, bone, and scale. The white flesh passed through the refiner's perforations is collected and referred to as first grade, while the portion rejected is put through the refiner again to recover the additional refined flesh, which is darker and less functional than the first grade. The second-time refined mince is, therefore, referred to as second grade.

The refined flesh is transferred to a screw press, which removes excess water. At this point, the flesh should be white, odorless, and residue free and have 82 to 84% moisture. Using a silent cutter, cryoprotectants sucrose, sorbitol, and sodium tripolyphosphate are mixed into the de-watered flesh at levels of 4, 4 to 5, and 0.2 to 0.3%, respectively. The levels and ratio of sucrose and sorbitol can be adjusted depending on the type of product to be made and the sweetness desired. Some surimi are prepared only with sorbitol, while some are produced only with sucrose but at a level no more than 5% because of sweetness. The principal steps of the rotary screen surimi manufacturing process are summarized in Figure 2.

The material balance of surimi manufacturing is shown in Figure 3. Most of losses occur during washing in the form of water-soluble proteins and secondarily from refining in which connective tissue is removed. Fine particles of water-insoluble myofibrillar proteins are also lost through the screen during draining. A variety of surimi are made from more than 60 different fish species. Each species requires slightly different processing techniques. Primary species include Alaska pollock, Southern blue whiting, Pacific whiting, and treadfin bream (Nemipterus tambuloides) in Thailand, which are processed in commercial volume for the production of frozen surimi.

Pacific whiting is caught off the U.S. West Coast, and its estimated production has exceeded 30,000 t in 1997.

Surimi Process
Figure 2. Flowchart of a pilot-plant surimi manufacturing process. Source: Courtesy of the Department of Food Science and Nutrition, University of Rhode Island.

Due to a strong parasitic proteolytic activity, Pacific whiting requires a special process that includes holding fish at below 5°C and the use of enzyme inhibitor such as beef plasma protein (1%) or egg white (2%) in mince prior to freezing. Currently, the surimi produced from Alaska pollock and Southern blue whiting make up the majority of the commercial production and command superior quality in terms of color, odor, and gel-forming ability.

The factory ship-processed surimi always commands high quality because of the freshness of the fish used and the prior removal of the backbone and belly flap. This leaves a minimum amount of blood and cavity residues with no autolysis (proteolytic degradation) in deboned fish mince, requiring less water in washing. Due to limited water availability, it is an absolute necessity for factory ships to have minimum washing using the freshest fish mince with minimum organ residues, whereas shore plants process boat-delivered fish, which could be one to five days old, depending on the length of the fishing trip. Thus, sometimes these shore-processed fish could lack freshness and produce a low-grade surimi. In the shore process, fish is often deboned without prior removal of the backbone and belly flap. Fish that is less fresh and has inadequate de-boning requires more extensive washing to remove proteo-lyzed products, blood, and other undesirable organ resi dues and fluids. The preceding explains why only two washing cycles are employed in the ship process, compared with three to four cycles in the shore process. The modern factory ship (Fig. 4) has the capability of processing surimi, as well as by-products such as fish meal and fish oil. The only limitation of the ship process is the water supply, which must be generated from seawater by desalinization.

Cryoprotectants were originally incorporated into the dewatered meat by a kneader or stone grinder; however, this incorporation is now accomplished by a high-speed cutter, which is more effective and faster than the kneader. Caution must be taken not to allow the temperature of the mix to exceed 10°C, above which protein functionality could be damaged.

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  • mari sandell
    How to process surimi?
    2 years ago

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