*2.3. Non-Reduced SDS-PAGE*

The original protein compositions of BL and Co were characterised by non-reduced sodium dodecyl sulphate-polyacrylamide gel electrophoresis (non-reduced SDS-PAGE) as follows. Solutions of 1% protein concentration were prepared. The volume fraction of concentrated gel (upper gel) was 5%, while the volume fraction of separated gel (lower gel) was 12%. No reducing agent dithiothreitol (DTT) was added; the protein marker was 16–270 kDa. Protein band abundance was expressed by relative optical density (%) measured using Image LabTM V4.0 software (Bio-Rad Laboratories, Hercules, CA, USA).

#### *2.4. Determination of Chemical Composition of PPI, CPI, Co, and BL*

Chemical compositions, including moisture (AOAC 935.29), ash (AOAC 938.08), protein (AOAC 2001.11), and fat (AOAC 920.39), were determined according to the methods recommended by AOAC [20]. Carbohydrates were calculated using the following formula: 100 − (moisture + ash + protein + fat).

#### *2.5. Preparation of Pre-Emulsion*

The protein powder of PPI, CPI, BL, and Co was used as an emulsifier to prepare pre-emulsified soybean oil [21]. The material was weighed using a mass ratio of m (protein powder):m (soybean oil):m (water) = 12:44:44. The protein was mixed with water, slowly stirred for two hours, and then mixed with soybean oil. The mixture was evenly dispersed with a T18 homogeneous shear machine (IKA Laboratory Equipment, Staufen, GER) at 11,000 rpm for one min in an ice bath, with a five-minute interval, and repeated five times and kept at 4 ◦C. At the same time, the blank control group without protein was established, and the homogenisation method was the same as that of M (protein powder):m (soybean oil):m (water) = 0:44:44.

#### *2.6. Preparation of Fish Sausage*

Formula: Fish sausage (g/100 g) was determined as 64.0 g fish meat, 30.0 g preemulsion, 3.0 g rice wine, 2.0 g edible salt, 0.5 g five-spice powder, 0.3 g tripolyphosphate, and 0.2 g pepper. In addition, 0.01 g sodium nitrite was added to prevent *Clostridium botulinum*. The fish-sausage emulsion in the blank control group was 26.4 g.

Marinating: Mince the fish into small pieces, add the marinade (soybean oil, edible salt, tripolyphosphate, five-spice powder, pepper, sodium nitrite) into it, and marinate it at 4 ◦C for 48 h.

Chopping: Mix the pickled lean meat with the pre-emulsion, then slowly chop and mix at a low temperature (10 ◦C) for five minutes.

Pouring: After eliminating the air pockets, use a small enema device to pour into the sausage casing, tie knots every 10 cm, count by weight, and control the diameter at about 2.5 cm.

Cooking: Fish sausage was placed in a 90 ◦C constant temperature water bath for 45 min, cooled in an ice-water bath for 15 min, drained of water on the surface of the casings, weighed and counted, and stored in 4 ◦C for 8 h.

#### *2.7. Cooking Loss*

The cooking loss (CL) of the gel was determined using the Youssef method [22]. The gel was cut into a cylinder of about 15 × 15 × 5 mm and weighed (W1), then put into a cooking bag and sealed. After cooking for 20 min in a 90 ◦C water bath, it was stored at 4 ◦C in a refrigerator for 24 h. Again, the gel was weighted (W2) after carefully blotting its surface with filter paper. The CL was calculated as follows:

$$\text{CL}(\%) = \frac{\text{W}\_1 - \text{W}\_2}{\text{W}\_1} \times 100 \tag{1}$$

where W1 is the mass before cooking (g), and W2 is the mass after cooking (g).

#### *2.8. Water Holding Capacity*

Next, we wrapped 8 g gel samples in double filter paper and placed them in a centrifugal tube before weighing the total weight. After centrifuging at 5000× *g* at 4 ◦C for 10 min, the gel was taken out and weighed. Formula 2 is used to calculate WHC, where M is the mass of centrifugal tube (g); M1 is the mass of gel and centrifugal tube before centrifugation (g); M2 is the mass of gel and centrifugal tube after centrifugation (g).

$$\text{WHC}(\%) = (\text{M}\_2 - \text{M}) / (\text{M}\_1 - \text{M}) \times 100\tag{2}$$

#### *2.9. Folding Test*

According to Kudo [23], the fish sausage was cut to a thickness of 3 mm and extruded between the thumb and index finger. The folding ability of the fish sausages was divided into five levels: (1) Sausage slices were broken into two pieces on the first folding; (2) sausage slices were cracked but not broken on the first folding; (3) sausage slices did not show any cracks on the first folding, but they were broken into two pieces on the second folding; (4) sausages slices did not show cracks on the first folding but did show cracks on the second folding; and (5) sausage slices did not show cracks even after the second folding.
