Hrf

Freezing

Wiener type

Sausage type

Figure 7. Flowchart of process for surimi-based emulsion-type products. Source: Courtesy of the Institute of Food Technologists.

the solubilization of myofibrillar protein. Next, for the improvement of texture and water binding, starch and egg white (raw, pasteurized, and frozen) are added with the remaining water, and the mixture is chopped for the remainder of the chopping period. Flavor is added during the last third of the chopping period for maximum delivery.

Starch

Currently, corn or wheat starch is used at around 6% to improve the textural properties of surimi gel, or at higher levels for cost reduction. Starch must be uniformly dispersed and gelatinized to strengthen the gel. Starch participates in gel formation as a dispersed phase, whereas protein does so as a continuous phase. Starch increases gel strength and elasticity through composite reinforcement and water binding. Gel-strengthening ability varies greatly from starch to starch. The gel-strengthening ability of starch is affected by its water-binding capacity during gelatinization and the viscosity of the gelatinized starch (40). The greater the water-binding capacity and viscosity of the starch, the greater is its gel-strengthening ability.

In general, strong, elastic gels are produced from unmodified high amylopectin starches, such as potato and waxy corn starches, which are less prone to rétrogradation at room temperature. In addition to the water-binding capacity and rheological properties of starch, its retrogradia-tion behavior and interaction with protein during gel network formation are also important factors that should be considered in studying the role of starch in surimi gel formation.

Despite the ability of potato starch and waxy maize to produce strong, elastic gels, the gels prepared with these starches have poor freeze-thaw stability and become rubbery and rigid with extended frozen storage. Addition of unretrogradable modified starch (hydroxypropylated type) greatly improves freeze-thaw stability, but it weakens gel strength in terms of elasticity and firmness. It is, therefore, advisable to use a proper mix of unmodified and modified starch to produce a desirable balance between gel strength and freeze-thaw stability. Starch modification through cross-linking in addition to hydroxypropylation has been a commercial practice to overcome gel-weakening problem associated with use of starch that is only hydroxypropylated.

Proteins

Addition of nonmuscle proteins tends to reduce gel strength and rubberiness. Nonmuscle proteins include egg white, milk protein, soy protein, and wheat gluten. The appropriate reduction in such textural properties leads to texture modifications and often results in an improvement of sensory quality. The gel-texture-modifying effect of non-fish proteins is closely related to their water-binding properties (41,42). Egg white is most commonly used in surimi-based products. Egg white is added in a raw form (<10%) on a surimi weight basis to enhance gel strength. When dry egg white is used, an appropriate amount of water should be added to adjust the moisture content in the finished product. Another important function of egg white is its ability to make the product whiter and glossier.

Hydrocolloids (Gums)

Gums being considered for use in surimi-based seafoods include carrageenan and alginate (extracted from seaweeds) and curdlan and xanthan gum (microbial extract). Among these ¬°-carrageenan gum has shown a gel strength improvement effect when used in either a dry or a cold hydrated form as low as at 0.2% (dry powder) (43,44). The gel-strengthening ability of gums highly depends on their firmness and elastic properties (45).

Cross-linking Agents

Microbially produced transglutaminase is being applied in surimi to increase the gel strength. The gel-strengthening mechanism involves cross-linking of myosins through the formation of nonsulfide covalent bonds between the car-boxyl group of glutamic acid and e-amino group of lysine during a cold setting, which requires several hours (Seki and Kimura). Therefore, it may not be useful for a highspeed production of crab analog, but suitable for some surimi-based products that require a cold setting as part of the preparation step.

Sodium ascorbate, not ascorbic acid, increases surimi gel strength with maximum at a 0.2% level (46). Its gel-strengthening effect is believed to be from cross-linking through oxidation of sulfhydryl (-SH) groups in proteins. Despite its gel-strengthening effect, ascorbate causes the surimi gel to undergo freeze syneresis with increased expressible moisture and rubbery texture development.

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