## 3 Results
### Fatty Acid Composition  
The fatty acid compositions of the lipids retained in protein isolates and hydrolysates from roach and B. herring are presented in Table 3. In the case of roach samples, all isolates and hydrolysates contained statistically significantly (\(p<0.05\)) more saturated fatty acids (SFAs)/total fatty acids (25.1-27.6 mg/100 mg total fatty acids) compared with the raw material (23.1 mg/100 mg total fatty acids). With the exception of the acidic isolate, all other isolates/hydrolysates contained statistically significantly less polyunsaturated fatty acids (PUFAs) (25.4-29.1 mg/100 mg total fatty acids) and more monounsaturated fatty acids (MUFAs) (45.8-46.9 mg/100 mg total fatty acids) compared with the raw material (34.0 mg PUFAs and 42.8 mg MUFAs of 100 mg total fatty acids). The fatty acid composition in protein isolates and hydrolysates of B. herring showed a similar trend in terms of SFAs, with all isolates and hydrolysates containing a statistically significantly higher relative content (26.6-35.3 mg/100 mg total fatty acids) compared with the raw material (25.5 mg/100 mg total fatty acids). The acidic and alkaline pH-shift isolate in particular contained a considerably higher proportion of SFAs (34.2 and 35.3 mg/100 mg total fatty acids), but also a lower proportion of MUFAs (32.1 and 37.5 mg/100 mg total fatty acids) compared with the raw material (25.5 mg SFAs and 41.4 mg MUFAs/100 mg total fatty acids). There were also significant differences in the composition of fatty acids within the same processing type (pH shift or enzymatic hydrolysis). For instance, in the case of roach protein hydrolysates, the one produced using Protemax had a statistically significantly lower relative content of SFAs and higher content of PUFAs than those produced using Neutrase and Corolase (24.9 vs. 27.0 and 27.6 mg/100 mg total fatty acids in the case of SFAs and 28.7 vs. 26.7 and 25.4 mg/100 mg total fatty acids in the case of PUFAs, respectively). On the other hand, acid- and alkali-treated protein isolates from both fishes had similar levels of SFAs, but alkali-solubilized protein isolates of both roach and B. herring had significantly more MUFAs (45.8 vs. 41.2 and 37.5 vs. 32.1 mg/100 mg total fatty acids) and less PUFAs (29.1 vs. 33.5 and 27.2 vs. 33.8 mg/100 mg total fatty acids) compared with acid-treated isolates of the same raw material. The varying amount of PUFAs could be related to different levels of loss through oxidation, and the possible differential distribution of lipid classes during fractionation. Interestingly, pH-shift isolates, especially acidic isolate from B. herring, had a significantly higher content of docosahexaenoic acid (22:6 n-3, DHA) (14.4 mg/100 mg total fatty acids) compared with raw materials (8.6-10.5 mg/100 mg total fatty acids) and enzymatically produced hydrolysates (6.4-9.2 mg/100 mg total fatty acids). Acidic isolates of both B. herring and roach also had a slightly higher relative content of eicosapentaenoic acid (20:5 n-3, EPA) compared with other protein isolates and hydrolysates (7.4 vs. 6.4-7.1 in the case of roach and 7.0 vs. 5.5-6.6 mg/100 mg total fatty acids in the case of B. herring), although the difference was not statistically different in the case of roach acidic isolate (7.4 mg) vs. Protemax hydrolysate (7.1 mg). The observed differences in fatty acid composition could be related to the differences in lipid classes remaining in either protein isolates or hydrolysates, e.g., PLs have been shown to display a higher level of unsaturation compared with TAGs.