## 3 Results and Discussion  
### Preliminary Results  
The sensory evaluations of individual fish burgers for taste, after-taste, odor, color, mouth texture, and overall acceptability are detailed in Table 1.  
The hedonic results showed the highest scores for carp burgers containing 0.5% and 1% of each microalga. Statistically, burger treatments with a higher microalgae concentration (1.5%) had lower sensory acceptability for all the organoleptic characteristics compared to formulations with the lower microalgae concentrations (\(p<0.05\)) (Table 1). The inappropriate taste caused by the addition of 1.5% of _Isochrysis galbana_, _Picochlorum_ sp., and _Chorella minutissima_ is related to the compounds obtained from lipid oxidation and to the minerals that not only act as pro-oxidant molecules but also might produce metallic off-flavors [24]. Yet, taste scores of carp burgers formulated with 0.5% and 1% microalgae were similar to the control fish burgers (Figure 1). The microalgae supplementation modified the conventional color of burgers to a darker one depending on microalgae content but not on microalgae species. Formulations with 1.5% microalgae had the lowest color scores (Table 1). Thus, burgers supplemented with 0.5% and 1% of microalgae were selected for further analyses so as to evaluate their physicochemical properties.  
The incorporation of microalgae into the burger composition had no effect on pH values (Table 2), something necessary for a better stability of fish products. Besides, there were no significant differences in fat and protein content between control and microalgae-fortified samples (\(p>0.05\)) (Table 2).  
These contents were confirmed qualitatively with Fourier-transform infrared spectroscopy FTIR analysis (Figure 1).  
The strong absorption in the region of 3200 cm\({}^{-1}\) corresponds to the hydroxyl (O-H) stretching vibration of proteins and residual water (Figure 1). The strong absorption in the region of 3000 cm\({}^{-1}\) and 2800 cm\({}^{-1}\) corresponds to the stretching of NH\({}_{2}\) groups, which reflects the high protein content in burger samples (Figure 1). The protein spectrum was characterized by the presence of absorption peaks at 1624 and 1522 cm\({}^{-1}\) attributed to the NH and C=O groups of amides I (1590-1650 cm\({}^{-1}\)) and the stretching of NH groups and asymmetric N=O groups of amide II (1500-1560 cm\({}^{-1}\)) [13]. The lipid spectrum was characterized by the presence of absorption peaks at 2922, 2852, and 1742 cm\({}^{-1}\) attributed to the Vas(CH\({}_{2}\)), Vs(CH\({}_{2}\)), and V(C=O) stretching, respectively, while the absorption peak at 1377 cm\({}^{-1}\) mainly showed the C-O stretching vibrations of carboxylic acids [13]. The absorption peaks found between 950 and 1200 cm\({}^{-1}\) showed carbohydrates (Figure 1). Compared to controls, microalgae-fortified samples did not show any specific absorption peaks. However, total solid (TS) contents were higher in burgers fortified with 1% _Chlorella minutissima_, 1% _Isochryssi galbana_, and 1% _Picochlorum_ sp. (\(p<0.05\)) (Table 2). Similarly, total dietary fiber values were greater in the burgers fortified with 1% microalgae. This might be the result of the high dietary fiber content of microalgae (Table 2). The high dietary fiber content of fortified burgers probably had an important role in their lower water activity (a\({}_{\text{w}}\)) [25]. This property serves to limit microbial growth and lipid oxidization and to optimize the physical characteristics of fish burgers. Similarly, the ash contents of the fortified burgers with 1% microalgae were significantly higher than those of the control burgers. These findings correspond to the results of other studies that indicate that these microalgae are rich in minerals [11; 26]. According to the results, carp burgers supplemented with 1% microalgae were chosen as the best final fish products and selected for other analyses to evaluate their textural, functional, microbiological, and antioxidant properties.