## 3 Results and Discussion
### Determination of the Optimum Composition of Laver Chip Batter through RSM  
The optimum composition of protein-rich laver chip batter through RSM was based on the results of preliminary experiments. Specifically, as shown in Table 1 (RSM 1), the ratio of laver and surimi was set and coded in 5 stages, from 20:20 to 28% (\(w/w\)) with increasing proportions of surimi, which has relatively high protein content. Air-frying time was set to 40-60 s in an air fryer (195 \({}^{\circ}\)C). The experimental design was then developed using the central composite design (CCD) method. In particular, 14 experiments were randomly conducted with 4 fractional points (No. 1-4), 4-star points (No. 5-8), and 6 central points (No. 9-14). The dependent variables were the brittleness and puffing ratio values.  
In terms of brittleness, the lowest value (6.16 N) was obtained for No. 6, which had 1.6 times the amount of surimi added to laver (20:26%) and was air-fried for 60 s. No. 8 (20:24%, 40 s of air-frying) showed the highest value (10.12 N). In terms of appearance and sensory evaluation, the laver chip air-fried for 40 s was not completely cooked resulting in a tough texture. Accordingly, the brittleness was also relatively high (No. 8). On the other hand, the laver chip air-fried for 60 s was burnt and had a bitter taste (No. 6) resulting in the lowest brittleness.  
In terms of puffing ratio, No. 5 (20:28% = laver: surimi, 50 s of air-frying) had the highest value (116.01%), while No. 2 (20:26% = laver: surimi, 45 s of air-frying) had the lowest value (114.33%). In all samples (No. 1-14), the puffing ratio ranged from 114.33 to 116.01%, with a variation of less than 1.46%. There was also no significant difference in appearance. The results of the multiple regression analysis of the dependent variables (brittleness and puffing ratio) obtained according to the central composite design are shown in Table 3.  
In the case of brittleness, when the layer content was fixed at 20% (\(w/w\)) and the surimi addition amount was increased from 20 to 28%, both the linear term (X\({}_{1}\)) and air-frying time (X\({}_{2}\)) were significant (\(p<0.05\)) in the first-order equation, but only X\({}_{2}\) was significant in the second-order equation, and all cross products were not significant. On the other hand, in the case of the puffing ratio, the two independent variables (X\({}_{1}\), X\({}_{2}\)) did not show significance in any of the first-order, second-order, or cross-product terms. In the case of brittleness, the lack of fit test and R2 values were 0.132 and 0.9897, respectively, which were satisfactory (\(p>0.05\)). However, in the case of puffing ratio, the values were 0.014 and 0.2728, respectively. Therefore, the design model based on the dependent variable, the puffing ratio was not suitable.  
Therefore, the optimization was performed with the goal of minimizing brittleness (\(<\)7 N) and achieving the average value of the central point measurement value (115.02% of puffing ratio). As a result, the optimization batter composition (laver: surimi: rice flour) and processing condition (air-frying time) were 20:21.3:58.7% (\(w/w\)) and 52.50 s, while the predicted values of brittleness and puffing ratio were 6.5973 N and 115.03%, respectively.