*3.2. Changes in Tissue Histology of Starch–Surimi Gels with Non-Setting or Setting Effect* 3.2.1. Light Micrograph

The morphology of potato starch differed appreciably between direct heated gels and two-step heated gels (Figure 3). It was observed that a nearly spherical morphology of starch was shown in SCG, whereas a relatively irregular state was observed in CG. Starch showed non-obstructive expansion in CG with 3% or 6% starch content. The striation structures inside of starch granules were intact with an increase in starch content, showing that the swelling degree of starch decreased in CG. In comparison, it was observed that potato starch granules in SCG were almost circular, especially in the low starch-containing matrices. In addition, large granule starch could not realize valuable swelling in two-step heating. However, regardless of non-setting or setting samples, small starch granules showed extended states, which was more conducive for applying starch in the surimi matrix.

**Figure 3.** Light microscopy of cooking gels and setting-cooking gels at four starch contents (3%, 6%, 9%, and 12%). indicates large granule starch; indicates small granule starch. Caption: see Figure 1.

3.2.2. Scanning Electron Micrograph

Overall microstructures of starch–surimi gels were observed at 300× to reflect the morphology of starch and surimi matrix after cooking (Figure 4). The gelatinization temperature of potato starch ranged from 56 to 66 ◦C, and the amorphous region extended after reaching this temperature range [30]. For CG, as the temperature rose above 45–50 ◦C, the suwari was partially disrupted, resulting in modori formation and unhindered starch swelling [31]. Moreover, the loose gel network might be a key factor of the irregular swelling of starch. In contrast with non-setting gels, SCG showed more substantial resistance to starch swelling that avoided water loss in the gel network structure. It might contribute to the setting step, which resulted in the formation of a stable surimi gel network in SCG. Thus, it could be determined that the setting effect promoted cross-linking in surimi, hindered water absorption, and broke hydrogen bonds in the striations of starch granules.

**Figure 4.** Microstructure micrographs (magnification ×300, ×3000) of starch–surimi matrix subjected with different heating processes: 0, 3, 6, 9, and 12 represented 0%, 3%, 6%, 9%, and 12% starch content, respectively. Caption: See Figure 1.

Viewed at large magnifications, non-starch containing CG exhibited a coarse matrix with large cavities, as shown in Figure 4. However, the addition of the starch made cavities disappear, resulting in more compact surimi. According to the results from Kong et al. [16], these shrunk surimi networks were considered to be responsible for the "packing effect." Meanwhile, for SCG, no significant changes were observed, and smooth structures were shown throughout the addition of starch.
