## 3 Results and Discussion  
### Proximate Composition  
The proximate composition of the samples is presented in Table 2. Overall, the concentrates contained more total lipids and ash compared to the hydrolyzed samples. All the samples were high in protein, but the hydrolysates had the highest protein content. With HYDR2 and COLL samples the ash content was remarkably low. With enzymatic hydrolysis, the soluble peptides are separated and collected from lipids and other insoluble matter but with heat treatment, the fat cells are merely ruptured, and the lipids are pressed out from minced raw material [6]. These differences in processing methods cause variation in the proximate composition. For the COLL1 sample, the conversion factor for protein is most likely too high, since the proximate composition is over 107% with the lipids, moisture, and ash taken into consideration. However, when we sum up the amino acids in the COLL1 sample (see Section 3.2.1 Amino acids), it sums up to 87.7 \(\pm\) 16.65 g or protein/100 g of sample. This is likely closer estimation of the true protein content. The part of fish used as a raw material in the fish proteins did not have an influence on the practical level the proximate composition of the samples, since the CONC2 (cod filleting by-products) and CONC3 (only cod backbones) had only minor differences between them. On the other hand, the results showed the effect of the raw material and the processing method on the lipid content of the samples. For example, in sample CONC1 (cod, saithe, and haddock), the lipid content was higher than in sample CONC2 (only cod). In addition, the HYDR2 (by-products of salmon filleting) had fewer lipids than HYDR1 (whole blue whiting), even though salmon is generally considered a slightly fatitier fish than blue whiting. The total lipid content of sample CONC3 was 4.2% in dry matter, which is less than previously reported in the concentrate made from cod backbone (8.8-9.3%) [29; 30] and more than reported with concentrates made from saithe and haddock fillets (0.5-0.6%) [31; 32]. The difference may be due to the processing or lipid extraction methods. Saithe and haddock fillets [31; 32] were analyzed with Soxhlet extraction, which is ineffective for extracting \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Sample** & **Protein (\%)** & **Total Lipids (\%)** & **Moisture (\%)** & **Ash (\%)** \\ \hline CONC1 & 63.0 \(\pm\) 0.00 \({}^{\text{a}}\) & 8.5 \(\pm\) 0.07 \({}^{\text{a}}\) & 4.2 \(\pm\) 0.11 \({}^{\text{a}}\) & 21.4 \(\pm\) 0.04 \({}^{\text{a}}\) \\ CONC2 & 70.8 \(\pm\) 0.00 \({}^{\text{b}}\) & 4.8 \(\pm\) 0.08 \({}^{\text{b}}\) & 4.0 \(\pm\) 0.21 \({}^{\text{b}}\) & 22.5 \(\pm\) 0.03 \({}^{\text{b}}\) \\ CONC3 & 69.3 \(\pm\) 0.00 \({}^{\text{c}}\) & 4.1 \(\pm\) 0.04 \({}^{\text{c}}\) & 5.3 \(\pm\) 0.81 \({}^{\text{ac}}\) & 19.1 \(\pm\) 0.02 \({}^{\text{c}}\) \\ HYDR1 & 82.9 \(\pm\) 0.00 \({}^{\text{d}}\) & 0.4 \(\pm\) 0.01 \({}^{\text{d}}\) & 4.1 \(\pm\) 0.03 \({}^{\text{ac}}\) & 9.8 \(\pm\) 0.40 \({}^{\text{d}}\) \\ HYDR2 & 93.4 \(\pm\) 0.00 \({}^{\text{e}}\) & 0.1 \(\pm\) 0.01 \({}^{\text{e}}\) & 3.0 \(\pm\) 0.01 \({}^{\text{d}}\) & 2.7 \(\pm\) 0.01 \({}^{\text{e}}\) \\ COLL1 & 99.3 \(\pm\) 0.00 \({}^{\text{f}}\) & 0.1 \(\pm\) 0.02 \({}^{\text{e}}\) & 7.8 \(\pm\) 0.01 \({}^{\text{d}}\) & 0.2 \(\pm\) 0.01 \({}^{\text{f}}\) \\ \hline \hline \end{tabular} \({}^{\text{Fish protein concentrates}}\) = CONC1–3, fish protein hydrolysates = HYDR1–2, hydrolyzed fish collagen = COLL1.  
\end{table} 
Table 2: Proximate composition of the commercial fish protein concentrates, hydrolysates, and hydrolyzed collagen with mean and standard deviation of three replicate measurements. Different letters within the same row indicate a statistically significant difference with ANOVA post hoc pair comparison (\(p\) < 0.05). fish oil [33; 34]. A study by [PERSON] et al. [35] found the lipid content of blue whiting hydrolyses to be between 0.0-3.0% of dry weight which is similar to the hydrolysate sample tested in this study (HYDR1, 0.4%).